Sun Bandit solar water heater
Hello. I was reading the article by Martin Holladay entitled “Solar Thermal is Really, Really Dead” and enjoyed the discussions going back and forth on the topic of solar water heating methods. I am planning on building a small 600sq’ SIP cabin in the area of Nelson BC (climate zone 6) next year and I found this product listed as being one of the most efficient for heating domestic hot water on the Canada Energy Guide site. It says it can also be used for space heating via a radiant floor system or perhaps radiators.
My cabin is going to be totally off grid. It is a simple rectangle measuring 34′ wide by 16′ deep with a small 8′ x 10′ air lock mudroom on the west side and a 3.5:12 pitch shed roof angled up to the north. The cabin is made out of Insulspan 12 1/4″ SIPs for the floors and roof and 8 1/4″ SIPs for the walls. The cabin will be built on helical screw piers since a concrete truck can’t get into the site. I’ve been going back and forth on various methods of heating the cabin and providing domestic hot water. At one time it was going to have an outdoor furnace and a radiant floor heating system but that seems overkill. I’d like to avoid having a wood fire indoors since most wood stoves seem to be much too powerful but I do plan on using propane for cooking.
The south windows are about 7.5% of the square footage, the west window is less than 2% and the north and east windows are less than 4%. All the windows are fiberglass framed, triple pane, argon with HSHG glass on the south side. The front mudroom door is solid and faces south into an enclosed screen porch which protects both the door and the west living room window from hot summer sun. The south overhang is 4′ deep and shades the south glass from May until September.
With such a small foot print my main concerns are efficiently heating the cabin but also providing hot water. As I’m the only occupant year round I am considering using a mini split for the heating but what to do about hot water? A PV array will provide all the electricity for a fridge, freezer and lighting. There is also an HRV located in an enclosed loft.
Any suggestion of products, combinations of systems or review of the Sun Bandit would be appreciated. Thanks.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Scott,
If your cabin were grid-connected, you'd have lots of possible ways to heat your cabin.
Since your cabin is off-grid, you really only have two options, in my opinion. You can heat your cabin with a wood stove. Or you can heat your cabin with a propane-fired space heater with through-the-wall venting. (Be sure to choose a model that doesn't require electricity to operate.)
I have reached this conclusion after living in an off-grid house for 41 years, and after helping many friends solve problems with their off-grid heating systems.
The main reason that you don't want to depend on a solar thermal system or a solar electric system to heat an off-grid house is that weather is often cloudy, and days are often short, and the sun is low on the horizon, when space heating is required. Batteries aren't able to store enough energy to keep a heating system going when you have three or more cloudy days in a row.
I'd consider a wood boiler and a large amount of water tank thermal storage. Ie, burn at the optimal rate and store the excess heat. But also propane so you can leave the place alone for awhile - and run a generator from it when solar fails.
Jon,
I strongly advise you to avoid the wood boiler -- the controls and circulator require electricity at a time of year when not much electricity is available.
Thanks for your replies. It's hard to know how much information to include with a question because you don't want to omit something important but then again you don't want to bog people down in endless construction details. I don't know if the floor plan came through so I'll try posting it again.
The cabin is designed to be built in stages depending on how much money I have available next spring. The main space is 16' x 24' with a kitchen, bathroom and living/dining/bedroom space. I don't want to climb a ladder so a sleeping loft is out but there will be a storage area above the kitchen and bathroom that can hold a HRV. The electrical and water utilities will be a short distance away from the cabin in a converted shipping container.
I had hoped to find some type of mechanical system that would combine space heating and hot water heating. I considered the Empyre Elite 100 indoor wood boiler to provide hot water for a radiant floor system and hot water but then I wouldn't need space heating all summer but would still need hot water.. That's when I started looking for solar water heaters like the Sun Bandit. I figured I could use it for the domestic hot water all year and add the radiant heating in the winter.
I have looked at the Empire direct vent propane heaters. Although I do plan to use propane for cooking I don't know if I want to be buying a lot more propane for heating. That's why I was also considering a Fujitsu 12RLS3H mini split. But that still leaves the problem about how to heat domestic hot water.
I guess what I'm aiming for is a "fairly" passive house. Nothing crazy like 2 foot thick walls but something that's tightly sealed and can get a good percentage of it's heat from the sun. I also want it to go up fast and be weather tight so I chose SIP panels and triple pane windows.
I expect one day that the energy grid will go down and people who are "off grid" will really be without any type of electricity. I do understand your concerns about not relying on equipment that needs electricity to use, Martin, but not using electricity doesn't leave a lot of options.
In the spirit of being totally "non-electric" I will mention one other product I found that doesn't need electricity. It's a hand operated well pump called the "Waterbuck Well Hand Pump". In case your well pump fails it's good to have a high capacity backup.
http://waterbuckpump.com/
Scott,
You want to live off-grid. That's fine. You need to stay warm during the cold, cloudy months of winter. That's the issue here.
You wrote, "Although I do plan to use propane for cooking I don't know if I want to be buying a lot more propane for heating. That's why I was also considering a Fujitsu 12RLS3H mini split."
If you don't want to buy propane for heating, that's fine. But you need fuel to keep warm during the winter.
I suggested a propane-fired space heater. If you don't want to buy propane, you can either:
1. Buy or cut firewood. But you'll have to be home every day to feed the fire.
2. Buy gasoline to keep your gasoline-fired generator going to produce enough electricity to run your minisplit. (Of course, you can get a propane-fired generator if you want -- but you already told us that you don't want to buy much propane.)
Choose your fuel. You're going to need some heat during the winter -- and if you're not grid-connected, you're going to have to provide some type of fuel to get through the winter.
I've given you advice based on my off-grid experience. I'll also tell you something else: Almost everyone who lives off-grid lives without an HRV. If a room feels stuffy, we'll crack a window open.
If you live off-grid, you're going to need to develop an entirely new way of thinking about electricity.
Scott. How big will your PV array be? Are you planning to be off grid because there's no grid connection available?
You'll need some major battery bank if you try to heat with a minisplit. Propane may be unavoidable if you want to go away in the winter.
I suppose the confusion I'm having in trying to select a fuel source for heating and hot water is that I keep reading articles on this site about Net Zero and Passive houses. Every one of them says that an HRV is necessary due to the fact that the building envelope is so tight you must have a system in place to refresh the air. I recall reading one article that stated that "opening a window is not sufficient to replenish the air inside a very tight house.
I also read that in comparing the costs between adding more insulation, installing a larger PV array, buying better windows or other such energy upgrades that the single most cost effective means of lowering your energy needs is building a tight shell. One article suggested using a fog machine inside the house to find out where all the cracks are. If your house is going to be that tight (and I'm planning on building the entire shell with SIPs and foaming and taping all the seams) then isn't an HRV necessary?
Because the shell is going to be so tight I'd like to avoid having a wood stove fill the air with fine particles from the combustion (which I think it would no matter how well sealed the stove). Besides the square footage a stove takes up there's also the mess of loading, running and cleaning it. Half the year it just sits there wasting space and it still won't solve the problem about how to heat DHW.
I am curious why several articles on this site (in discussing Net Zero and Passive house design guidelines) suggest adding solar thermal to reduce energy needs? I take it you use propane for space heating in your home with perhaps a small wood stove for backup but how do you heat your DHW Martin? If the best choice is propane then I will use propane but if articles are suggesting solar thermal then which solar thermal systems do they recommend?
As to electricity usage, I plan on having a GE fridge rated at 328 kWh/yr, a Danby Designer freezer rated at 189 kWh/yr,, a small kitchen hood fan vented outside, some LED lighting and the usual electronics.in addition to any building systems like an HRV. I plan on maybe a 3Kw system and using those salt water batteries. The site is quite remote so grid power is out.
I was hoping that some type of solar thermal system would work but perhaps the indoor wood boiler is the next best thing.
Your description of the design features of a net zero house is accurate. But you aren’t building a net zero house. It’s impossible to achieve net zero with an off-grid house -- at least in Canada, where you live, because you need electricity during the winter, when a PV system can’t provide much electricity. (There are two exceptions: if you live at a very windy site, and you can erect a large wind turbine, or if you live near a year-round stream where you are legally allowed to install a micro-hydro system, your off-grid house might be able to get you through the winter without propane, gasoline, or firewood.)
A net zero house has to be grid-connected. The way a net zero house works is that the grid is used as a giant battery. The PV system feeds extra electricity into the grid from March to September, and obtains a credit for that electricity from the electric utility. And from October to February, the owner of the net zero house draws down that credit, using more electricity from the grid than the PV system can supply.
It isn't reasonable (or affordable) to install enough batteries to store electricity for more than about 3 days. In theory, you could buy $20,000 or $30,000 worth of batteries to stretch the length of storage time a bit further -- but maintaining such a large battery bank is a big pain. It's always cheaper to run a generator than it is to buy enough batteries to keep your house going for a week.
Since your house won’t be grid-connected, it’s not going to be net zero. You have to choose some type of fuel to burn during the cold, cloudy months of winter.
If you want to install a propane-fired generator and a large propane tank, you can enjoy almost any electrical gadget you want, all winter long. When your generator is running, your electricity will be expensive -- but all your gadgets will work. That said, most off-grid homeowners do their best to choose systems that won’t require lengthy spells of generator use during the winter, because generators are expensive; running them is noisy; maintaining them is a pain; and the type of electricity they produce is extremely expensive -- so expensive that an off-grid house would never use a minisplit heat pump for space heating.
In your latest comment, you asked again about whether an off-grid house should have a solar thermal system. As I wrote in my article, “Solar Thermal is Dead,” “Solar thermal systems still make sense for off-grid homes.” (The reason is simple: since off-grid homes don’t have access to cheap electricity or cheap natural gas, those of us who live off grid pay more for energy than grid-connected homeowners. That means that it makes sense for us to buy expensive equipment, like solar thermal equipment, which may not be cost-effective for grid-connected homeowners.)
Since I live in an off-grid house, I have a solar thermal system to make domestic hot water. Since my solar thermal system can’t make any hot water during the winter, I use my wood stove to make hot water for half of the year.
It doesn't make sense, as you suggest, to use a wood boiler for space heat. A wood boiler uses too much electricity for an off-grid house. In fact, any type of hydronic system is a bad idea, since hydronic systems need circulators. Keep it simple -- buy a propane-fired space heater that doesn’t use any electricity. Or, if you want to burn wood, use a simple, old-fashioned wood stove, without any bells or whistles.
If I were you, I’d give up on the freezer. I’ve never met an off-grid homeowner who had a freezer as well as a refrigerator. I advise you to learn to live with the small freezing compartment of an efficient refrigerator/freezer.
Thank you Martin for taking the time to answer my questions. I imagine that as a GBA advisor you are a bit of a lightning rod for attracting every kind of possible question under the sun. In considering your comments about wood heat I have reconsidered the stages of the cabin build. All along I was planning on adding a small bedroom space to the north wall of the living room and moving the Murphy bed there. The spot where the bed unit used to be would have a small wood stove.
I like the idea of a Murphy bed since that extra room could be also used as a TV room, office, music room, etc. If I build this room first I can add the wood stove and the dining area and pantry could be built later on.
I do have a lot of storage space above the mudroom entry, kitchen and bathroom to hold any mechanical equipment. In looking through all the articles I've saved from various sites I found one entitled "Optimization of Net Zero Energy Houses" by Gary Proskiw. In it he talks about ventilation for very tight homes and asks "Why don't people just crack open a window"? He says that doesn't really do anything for someone that is trying to maintain a tight building envelope. As it is my cabin only has two operable windows (the west living room window and the east bedroom window). I've also read articles about using "exhaust only ventilation systems" but other people suggest that the saving of energy from a HRV is still a consideration in a colder climate.
The best parts of articles I read by people who have a lot of real world experience usually deal with the "what would I do differently" topics? In looking at the Sun Bandit how does that compare to the solar thermal system you use? What model of wood stove would you buy now to include water heating? Would you recommend just an exhaust only system and in what form?
Here's the plan as it stands with the wood stove location included. Thanks for you guidance.
Scott,
Those of us with OCD appreciate the way your dimensions all work on two foot increments. I don't know if it affects the SIPs, but if you were free-framing the cabin that helps a lot. Any chance you could increase the size of the Living Area to 14'-0", which would make the bathroom an even 10"-0"? I'd sleep better tonight if you did :)
Scott,
Gary Proskiw (and everyone else who advocates a mechanical ventilation system for a very tight house) is right. For most Canadians and Americans -- people who live on the grid -- the best way to ensure indoor air quality is to install a mechanical ventilation system. That works a lot better than expecting people to remember to crack a window.
An off-grid cabin is different from an average home. If you go to bed while your HRV is running, you'll wake up in the morning and notice that your battery voltage has dropped. That may be OK, as long as you don't mind starting your gas-powered generator every time you notice that you have a low-voltage problem. Most of us who live in off-grid cabins want to have as few continuously operating electrical loads as possible, though.
If you want a ventilation system for your off-grid cabin -- because you feel uncomfortable with my advice to crack a window -- then you should buy a Panasonic WhisperGreen exhaust fan that uses about 13 watts. That's fewer watts than any HRV on the market. (An HRV may save some thermal energy, but in an off-grid cabin, you're not worried about thermal energy, especially if you have a wood stove. You're worried about electrical energy, which is very expensive to make during the winter.)
Scott,
Q. "In looking at the Sun Bandit, how does that compare to the solar thermal system you use?"
A. The Sun Bandit appears to be an electric-resistance water heater connected to PV panels. Your house will already have a PV system, I assume, so you don't need to buy the Sun Bandit. If for some reason you want to have two more PV modules (like the ones that come with the Sun Bandit), just buy two more PV modules and add them to your existing PV system.
The Sun Bandit system includes an electric resistance water heater. I don't think that's a good choice for an off-grid home, because your house won't have a lot of extra electricity, especially in winter. During the summer, you'll probably end up using a solar thermal system to make hot water. During the winter, the simplest way to make hot water is with a propane-fired water heater (either a tankless model or a tank-style model -- but be careful, you want to buy a water heater that doesn't require any electricity).
Q. "What model of wood stove would you buy now to include water heating?"
A. In previous years, several wood stove manufacturers offered stoves with a hot-water coil as an option. The hot water coil can be connected to a thermosiphon loop; this loop is connected to a water tank above your wood stove (upstairs).
Stove manufacturers aren't offering hot-water coils any more, due in part to EPA regulations, and in part to worries about homeowners who don't know how to hook up the water coil and end up with an exploding stove.
If you want to put a coil in your wood stove, your best bet is to buy an older steel wood stove and install the coil yourself. That's what I did. Two points are important: (a) You had better know what you are doing when you design the system, because these systems can explode. (b) These systems aren't the first choice if you intend to leave your cabin unheated for periods of time during the winter, because the entire system has to be drained.
Thanks Martin for your reply. It seems in every step forward I have to take two steps back. So far just about every system or product I've considered for my cabin has proven to be too costly, too large for the cabin or needs too much electricity to operate. I've read that you've been living in an off grid home for almost 40 years now. It must be frustrating to write about so many great advances in solar design, construction methods or energy efficient products and not be able to utilize them in your own off grid home because of the energy required.
I was wondering if you would consider writing a couple of blogs about what you would do if you were starting out today to build an off grid cabin like mine? I'm considering SIPS for the entire building envelope but I've also considered using SIPS for just the roof and floor with an additional false floor throughout to have a place to run the drain lines. I've thought of using a 2x6 wall with 2 inches of roxul mineral wool boards on the outside, 1/2" of strapping and metal galvalume siding. I planned a cool roof with standing seam metal panels over the SIP roof (I think SIPS are the quickest, easiest method for the roof and floor but maybe I'm wrong). In essence I'm trying to create a quick to build, tight building envelope along the lines of what is recommended for a Net Zero house. Something that gets as much energy from the sun passively and won't overheat.
That said, the area I'm having trouble with are the mechanicals. All SIP manufacturer's say mechanical ventilation is mandatory not just for fresh air but also to remove the interior humidity. In reading some GBA articles I have heard of supply only and exhaust only systems (as well as a product called a "Lunos fan") as being possibilities. The heating method is now down to a wood stove and a propane heater backup. Hot water seems to be the sticking point. How to get hot water in summer when you don't need space heating and in winter when solar panels don't work well.
So (in throwing a tremendous amount of work your way, Martin) if you were heading out to build my off grid cabin today what would you change, include or eliminate from the plan? Which products would you buy or construction methods would you choose? I ask because you're much farther down the road knowledge-wise than I am and I find it frustrating that so many products, methods or systems developed over the last 40 years simply won't work (or work well) in an off grid home.
Scott,
If you are venturing into the woods to build a cabin, re-read Thoreau's Walden. There must be a reason that you are choosing an off-grid site.
I'm assuming that you like the remoteness. You like nature. You like simplicity. You are taking a different path from the average North American homeowner.
Enjoy the woods. You're going to be living a much simpler life that most people do these days. You're going to be using less energy. You won't have as many gadgets. That's why you, and Thoreau, chose the path you are taking.
If you're having second thoughts, maybe you should buy a lot in a suburb, and hook your house up to the grid.
Actually, Martin, you've hit the nail on the head. It seems to me that in the last 40 years all the development of sustainable building ideals, energy efficient products and improved construction methods aren't really applicable to someone that wants to live sustainably off grid. The choices are either "buying a lot in the suburbs and hooking up to the grid" or "heading out into the woods to live like Thoreau".
In the course of my reading I've been back and forth on every kind of building technique and mechanical heating, ventilation , DHW and cooking method possible. I've looked at all kinds of wall systems, roof systems, waste water systems, heating and ventilation systems and each time I think I've found a solution it turns out that "this uses far to much energy to use in an off grid home".
As an example, in looking for a cooking method I found an article on induction cook tops. "Uses 70% less power than a regular electric stove!" it said. Later on I discover it could never work with a PV array.
I thought an indoor boiler would be best for heat and hot water. "Get free hot water at the same time you heat your home! All with firewood you cut from your own land! Turns out it produces far too much energy for such a small house. Then I read several articles suggesting that a "small ductless mini-split" is the way to go. Nope. Still draws too much power for an off grid home.
So after 40 years of steady improvements in PV, lighting, appliances, building materials and just about every other aspect involving passive solar home design it still comes back to using a wood stove with propane backup for cooking and DHW.. There doesn't seem to be anything new between the suburbs and Walden's Pond and that's a shame.
Scott,
The one area you might find some fruitful technological innovations are systems designed for RVs or boats, which face the same dilemmas you do.
Scott,
A lot of off-grid technology is spectacularly better than it was 40 years ago -- especially lighting. I love LEDs. Inverters are now more dependable (and more efficient) than they used to be.
The choices aren't really between the suburbs and Walden Pond, even though I told you to consider those two contrasting poles. And I disagree with your conclusion that "it's a shame" that off-grid homeowners can't use a lot of electrical gadgets. I don't miss the gadgets, and I don't think it's a shame I can't own them.
I live where I do not so that I can try out all the latest electrical gadgets. I live where I do because I can put on my cross-country skis near my front porch and go off in the woods for an hour and not see anyone, and I can spend my time puzzling whether the fresh tracks I'm looking at were made by a large deer or a small moose.
Two more points:
1. Amory Lovins said something to the effect that "homeowners don't want electricity; they want hot showers and cold beer." You will be just as warm and comfortable in your house heated by a wood stove and a propane heater as the guy who lives in a house heated with a ductless minisplit.
2. If you are trying to be environmentally responsible, remember that urban residents who live in grid-connected apartments are more likely to lead a "green" lifestyle than people who live in a remote off-grid cabin.
Thanks for your reply, Martin. I think what's frustrating me is the lack of information geared towards those people who want to build a tight energy efficient house and also live off grid. Most of the products or "solutions" offered to people who are interested in sustainable building, Net Zero houses or passive solar aren't suitable in my situation.
My frustration isn't completely tied to choices over mechanical systems but also to building envelope design. I understand that conserving energy is more important than producing energy. What's the point of having a 98% efficient heating unit if all the energy is leaking out of the building? As far as I know SIPs are the beat method of creating a tight home, preventing both air and water infiltration as long as the seams are correctly sealed and taped. But how to get the stale, moisture laden air out of the building? What to do about propane cooking fumes and bathroom exhaust? I've read several articles on this site dealing with these subjects but the solutions all seem better suited to a grid tied PV system. Do you think that Lunos system might be best?
Let's see. Standing seam metal Galvalume roof over a cold roof over the 12 1/4" roof SIPs. Walls are 8 1/4" SIPS with maybe 2" of Roxul Comfortboard outside of that with 1/2" furring strips and metal siding. 12 1/4" SIP floor on beams on top of Techno Metal Post helical piles. Inside there a 6" deep false floor throughout for plumbing pipes and electrical. Triple pane fiberglass windows with high SHG glass on the south side. Windows are 7.5% of floor area on the south, 2% on the west, about 2% on the east and north sides. There's a 3 foot overhang on the south side. The bedroom has a 12 1/4" SIP flat roof. There are 2 small venting clerestories on the north wall of the living room.
I think for space heating I'm going to go with a Tulikivi masonry fireplace. Might as well hold the heat in a nice soapstone fireplace. Cooking will be propane, fridge will be electric. I might still get a small freezer but no dishwasher, washing machine or dryer. There's a TV, dvd player, computer, LED lights. Well will be a hand pump Waterbuck. Apparently the fireplace can come with a water coil. Propane backup for DHW. What else? Small appliances-maybe a toaster.
Other than figuring out the ventilation system am I forgetting anything?
Scott,
Have you read this series of blogs on building an of-grid house near Ottawa?
https://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/building-grid-home-canada
Scott,
The link provided by Malcolm is worth reading. The blog series by Craig Anderson discusses a house — a bigger house than the 600-square-foot cabin you are designing. Craig Anderson shows that with a big enough budget, it’s certainly possible to build an off-grid house with almost all of the comforts of a modern North American house.
You are once again lamenting the fact that solutions that are appropriate for a net-zero house (that is, a grid-connected house) won’t work for an off-grid house. You’re right about that fact, but I don’t see why that fact is cause for lamentation. You’ve been sitting at the wrong lunch table in the school cafeteria. Instead of sitting at the net-zero table, you should have been sitting at the off-grid table.
A great source of basic information on off-grid house design can be found at the website of a company called Backwoods Solar Electric. If you prefer, you can order their paper catalog — a catalog that includes essays to guide you. If you become a customer, purchasing the equipment they sell, they’ll provide excellent advice over the phone.
You wrote, “As far as I know SIPs are the best method of creating a tight home.” If you want to build a SIP home, you should. But you should also realize that many GBA readers would probably disagree with you on the question of whether this is the “best” approach. It’s an approach, for sure, but it’s not necessarily the best.
You seem particularly worried about ventilation. For a 600-square-foot off-grid cabin, your three best options are (a) opening windows when needed, or (b) an exhaust-only ventilation system using a Panasonic WhisperGreen fan, or (c) a pair of Lunos fans. Any one of these approaches will work.
In your most recent post, you inform us that you plan to install a Tulikivi masonry fireplace. I’m surprised. (You’re the kind of GBA reader that I call “advice-resistant.”) That’s serious overkill for a 600-square-foot cabin, and it will set you back about $18,000. I’ve suggested a simple wood stove; here in Vermont, you can have your pick of used wood stoves for $100 to $800. But it’s your money.
http://www.newsminer.com/news/local_news/builder-uses-solar-power-to-heat-fairbanks-home-in-the/article_0e6654f8-6226-576b-a004-2870890894cb.html
Richard,
I'm not sure whether the link to the article about Thorsten Chlupp's home (which has been discussed several times on the GBA site) is relevant.
In case the basic facts are unclear, here they are: (a) Thorsten Chlupp's home was quite expensive -- it includes an elaborate system for storing thermal energy, a system that fails the cost-effectiveness test -- and (b) the house is grid-connected.
Martin, you're right that I am concerned about ventilation. This is basically because of the different sources of contaminants located inside the cabin. I'm worried about moisture buildup due to the very tight building envelope. All SIP manufacturers maintain that an HRV is a mandatory piece of equipment for air quality. In reading through several GBA articles I find that a primary concern for that type of construction is warm indoor air carrying moisture into the seams and rotting the panel edges. This was most notably mentioned in the article about SIP roof failures in Alaska. The better sealed and taped the seams the tighter the house and therefore your chances of replacing stale air without a HRV s severely compromised.
If, however, an HRV is more suited to a grid tied home due to it's need for constant power as you mentioned then I'm left casting about for a possible replacement. Quite by chance I stumbled across a mention of a Lunos fan system. This seems like a promising solution. I also plan on having a bathroom fan and will use the Whisper Green fan you mentioned. I will also be using a range hood fan in order to keep grease and cooking fumes (as well as the propane byproducts from the cook top) separate from any other ventilation unit.
My primary concern about an exhaust only fan system was that possible negative pressure caused by the fan might cause back drafting if a wood stove was also present. I've been resisting a wood stove due to the relatively large area needed to place the stove as well as the mess and particulates emitted into the room. I also didn't like that metal stoves heat up quickly and produce a dry heat but then cool off quickly. A soap stone stove is more like a beautiful piece of furniture and if I use one of the smallest models I will have to only fire it once at 5:30 PM to enjoy almost 18 hours of warmth.
I'm not resistant to advice. I do appreciate all your guidance but I must admit I was a bit discouraged when I read through one of your blog postings about a conversation between you and a neighbor and all the winter problems you were both having with frozen pipes, etc. At the end you said that you were a "bunch of old hippies living in leaky cabins and that we should learn from your mistakes". I thought "Really? In 2016 you have to make do with leaky cabins and frozen pipes if you live off grid?"
I'm hoping for something better. To be honest, I foresee a day when electricity may not exist in the form we have now. Perhaps small individual PV systems may be all we have. Still, I'd like to include modern conveniences where I can. Perhaps, as I suggested, you could write those blogs about what you would do if you were starting out today to build your off grid life using todays products and construction methods. I really would like to learn from your mistakes.
Martin ,
The relevance is that it is solar thermal which contributes to heat and hot water and it has radiant heat as a component . The fact that one is grid tied and one will not be is really just another part of the discussion . Your readiness to count others money as if that is what is asked of you still astonishes . A Tulikivi is a nice idea , a W10 is even one step since it can heat water in a small tank which can store hot water ( Voila) and be used for the few hours of space heating Scott will need possibly during the we morning hours when the stored heat from the stone is not enough . Small ECM circ or 2 does the job easily in an off grid situation .
You don't get what you don't pay for . I can only offer ehlp to those who ask for it and subscribe to the same theory as Scott , in that we can all learn from our mistakes and it is cheaper to learn from others' mistakes . Discounting things because others failed for any number of reasons is plain stupid . The mistakes made in projects past has been learned from , maybe you should open up your mind . I know you were invited to attend a presentation a couple weeks ago at a certain event , maybe you should have attended , you may have gained some knowledge .
Scott ,
I have not yet looked at the SunBandit but will over the weekend . I will certainly post my thoughts on it for your review .
Richard,
I stand by my advice that a Tulikivi masonry stove is overkill for a 600-square-foot off-grid cabin.
And, like both you and Scott, I'm a strong believer in learning from others' mistakes. I have never held up my own house as a model. I'm sure that anyone with half a brain can build a house that is tight enough and well insulated enough to avoid problems with frozen pipes. Unfortunately, when I built my house 34 years ago, I didn't have half a brain.
This is basically an advice column. People who post questions here are seeking advice. GBA readers (I'm one of them) provide advice; our advice is free, and it's worth what people pay for it.
The wonderful thing about this advice, freely given, is that it can be freely ignored. If Scott wants a Tulikivi masonry stove, we all know that he can, and will, install one. That's fine. It's his house.
Scott,
You are wise to worry about choosing a thermal envelope that is so fragile that it might rot if you don't operate a ventilation system. That would be a fragile thermal envelope.
If you are certain you want to use SIPs, I think that you can fully avoid the risk of rot by (a) using interior tape at the seams in addition to spray foam at the seams, and (b) including a rainscreen gap on the walls and a ventilation gap on the roof between the SIPs and the roofing.
It sounds like the Lunos system will be a good fit for your needs.
There is no need to have a wood stove if you don't want one. One (or at most two) propane space heaters will take care of your heating needs. Your heating requirements will be small if you build a tight, well-insulated envelope. A wall-mounted propane heater will take up much less room in your 600-square-foot cabin than a Tulikivi masonry stove.
Thanks everyone for your replies.
I chose SIPS because of the fact that the structure, insulation and vapor barrier are all in one product. Building out in the woods using a stick method seems to me to be counter productive. I also think it is difficult to get a high enough R rating for the floor and roof system if they are built with 2x lumber. By using SIPs for the 3.5:12 pitch shed roof I don't have to provide any baffles, air channels, vapor barrier or vents. Just simple flat panels resting on top of exterior walls and a couple of ceiling beams. On top of the roof will be a 1 1/2 inch vented cold roof with plywood on top of furring lumber and then a corrugated metal galvalume roof. The only hole in the roof would be for a fireplace flue.
The floor is also going to be SIPs. They'll rest on 6 x 12 beams but in order to run any plumbing drains or electrical wiring there will be a 6 inch false floor throughout.
I've gone back and forth about the walls being SIPs or not. It would certainly be quicker building them out of SIPs and ordering everything at once from the same company but then I think 2x6 construction would be cheaper. The main disadvantage to building the walls with 2x6's is that so many more layers have to be properly cut, joined together and sealed properly in order to be air tight. I think adding a layer of Roxul 2" Comfortboard to the outside of the SIPs would work along with the drainage plane.
As to the Tulikivi fireplace, their smallest model will heat 900 sq' with one firing per day using 17 lbs of wood per firing. I like that the stoves emissions are rated better than the most stringent air quality guidelines in the world (currently Austria's). I also like that you don't get a "blast of heat" right away and then a rapid cool down like with most metal stoves. If I have to look at a stove all summer long when I can't even use it it might as well look fantastic. When I add the addition the cabin will end up being 755sq' and I might only need to fire the stove every 30-36 hours instead of every day.
As to the propane wall heater the smallest "Empire" model I saw was the DV210SGX rated for 10,000 BTU's. Looking at my plan I have very little available wall space to put it. Could it go against the west living room wall and vent out into the screen porch? I wouldn't be sitting out there in the winter when I needed t use it. The other option would be on a shelf at loft height overlooking the living room (or is that advisable?)
Martin, in your study of solar thermal units for DHW, I was wondering what you thought of evacuated tube water heaters? They seem to be ideal for cold environments and will be much better at producing heat than a flat plate collector throughout most of the winter.
Scott,
With the Tulikivi stove as the sole heat source, i'm left wondering how you will modulate the indoor temperature. That every thirty hour burn will have to be pretty accurately gauged for the house to maintain an even temperature without cracking a wind -. something you don't seem to want to do.
Malcolm, The Tulikivi model I am looking at reaches 100% of its heating capacity 2 hours after the fire is lit, then capacity reduces to 50% after 8 hours and hits 25% at around 18 hours .I'm hoping that since the cabin will be small and air tight the heat will be sufficient if the stove is lit every 30-36 hours. However, time will tell. Even if I have to light a fire every 24 hours it will be less work and a more pleasant heat than using a metal stove. I'm also hoping that the passive solar considerations I've built into the plan with window sizing and overhangs will allow me to capture a fair amount of heat during the winter. Still, it is good advice to include a direct vent propane heater In case I need supplemental heat during a very cold snap or if I go away for a few days.
Scott,
For several days now I have been reading this thread with much interest but this is the first that I have had time to comment. I am in the process of building my own off-grid home in Ontario so I am somewhat on the same path that you are on; but my comments pertain more to the process rather than the exact details of what you are doing.
When I built my first house (1976) it was relatively easy - follow a few guidelines, try to make sure the roof doesn't cave in and add everything else as required. I built a geodesic dome and the only question asked when I got a permit was how to spell geodesic. It worked fine, was heated with wood and I lived in it for 35 years. I also built a log cabin (1996) that I am presently living in. It was uncomplicated to build, is heated with wood and also works just fine. I guess my point is that whatever you build will work just fine for you (eventually, after fixing the mistakes :).
The house I am building now has been an entirely different experience (although still just as enjoyable). I wanted to build something that was off-grid, artistic, energy efficient, low maintenance and indestructible. We have access to electricity so there is no pressing reason to build off-grid but it is the way that my wife and I want to live so that is what we are doing.
However, building is no longer a simple process. For a non-professional builder to build a "pretty good house" using modern building techniques requires a huge amount of study and perseverance. The choices are overwhelming, the experts do not agree on the best way to do anything (otherwise we would not be having this discussion), costs escalate rapidly, sourcing of materials is difficult and everybody wants to sell you something (and that something may not necessarily fit well with what you are trying to build).
From what I have read, it seems like you may be a first time builder and are overwhelmed with the choices. If your choice is to be off-grid, then this becomes the critical path and everything that you design has to be tested against the reality of off-grid existence – if something uses a lot of continuous power then it doesn't matter whether it is "modern technology" or how high tech it is - you don't want it. For the record, I considered and then rejected the use of SIPS for my house and I also think a Tulikivi type stove is expensive overkill. Overall, I think that the best advice you will get for your project will be from someone who has lived off grid for forty years or so.
Scott - One thing that may be worth noting in your consideration of a masonry heater: It is true that you will have to load a woodstove more frequently than a masonry heater. In a small, tight building, I think it would be reasonable to expect to reload a right-sized stove at least every 12 hours. However, you load that stove, fifteen minutes later you shut the air down...and then you go about your business for 12 hours. With a masonry heater, if you want to keep all that nice heat you built up, you ain't leaving until the last ember dies. Check out tulikivi's end of firing instructions if you weren't already aware of that.
Scott,
Your cabin is so small and so well insulated that it won't take much wood to heat. What I was suggesting wasn't a criticism: I think you should plan to over-heat the place a bit with the Tulikivi and leave a window open both to modulate the temperature and provide ventilation. The energy penalty, in terms of how much additional wood you will need, will be very small.
Scott,
If you have finalized your plan for heating your cabin, then you don't need our advice on the matter.
If, however, your HVAC plan is not yet finalized, then you need to be flexible enough to modify your plans as necessary. No one can finalize their plans if they have not yet chosen a heating system. If, once you have chosen your heating system, you have to move a closet or a wall to accommodate the equipment, that's normal. That's what the design process is all about. It's better to make these changes to your plan now than on the job site, after the walls are built.
So adjust your plans as necessary to make room for your propane space heater -- if, that is, you want one.
One more point: If you decide to stick with the Tulikivi as your only heating source, you will be crossing your fingers every time you go away on vacation and leave the house unoccupied, hoping the house doesn't freeze. The advantage of making room for a propane space heater is that you can leave for a few days in winter without worrying that the house will freeze. That's why you probably want the propane heater in any case -- even if the Tulikivi becomes your primary heating source.
Scott,
Your foundation plan is not ideal. If you build your house on piers, how will you keep your pipes from freezing? You can't just build a chase, put your pipes in the chase, and insulate the chase. The pipes are likely to freeze in the gap between the top of the soil and your floor. (It's even possible for your drain pipe to freeze. If you want to hear the story, you can ask me how I know.)
Grid-connected homeowners solve the "house on piers" problem with electric heat tape. This solution doesn't work for off-grid homeowners.
You need a basement, crawl space, or slab on grade.
Scott,
Q. "I was wondering what you thought of evacuated tube water heaters?"
A. Although I have no direct experience with them -- and I'd be a little worried about their fragility -- everything I've read about them leads me to believe that they work just fine.
Scott,
I have not used any of these, but Empire, Williams, US Stoves/Ashley and Cozy all produce small direct vent LPG wall furnaces that do not require electricity. I have been looking for a heater that varies output according to demand, the Rinnai C Series will do that and has higher efficiency but it does require power - 1 watt standby - I have not yet found what the power consumption is when operating.
Rob,
The Empire units that I am familiar with do not vary their output; they are basically either on or off. But (a) they do not require electricity, and (b) they are thermostatically controlled by a wall thermostat. You set the temperature where you want, and the Empire unit keeps the room at the setpoint. (I think that the tiny amount of electricity needed to operate the thermostat is supplied by a thermo-electric generator that is warmed up by the pilot light.)
Thanks everyone for your replies.
Rob, you are right that building a modern energy efficient home is no longer easy (if it ever was). The sheer volume of new products, methods of construction and finishing details is overwhelming but I do consider myself flexible to making changes. So far I've gone from an indoor wood boiler with a radiant floor to a wood heater with propane backup. I find what causes most of the changes to my plans is discovering some little tidbit of information tucked away on page 3 of an article somewhere and realizing "this is important! I need to change this". For example, in looking at articles on kitchen range venting I found links over to articles on the indoor air pollution produced from cooking with gas. Needless to say this interested me because I'd just discovered that an electric range or cooktop was out of the question in an off grid home and I was now looking at propane. I read that the moisture and other byproducts produced from burning propane can fill your home with plenty of dangerous particles and that proper venting was critical. This is part of the reason why I was resistant to add another propane device to the cabin and I'm also considering isolating the kitchen more so that I can close it off from the rest of the cabin while the propane fumes clear.
Moisture control has also governed my search for a proper ventilation system. SIPs are so tight that they trap moisture inside. The last thing I want is warm moisture laden air leaking through the SIP seams and rotting the panels. To my mind there is no better product for a cathedral ceiling (which is what my shed roofed cabin will have) as well as the floor. Just set them in place, seal the seams and you're done. I think the Lunos fans would work well and I've also seen another product called Comfoair that might be better (a higher rate of air movement).
As to the foundation, if I could get a concrete truck out there I would go for a slab on grade foundation. I would not consider a crawlspace foundation due to the large number of articles I've read about how poorly they can be built and the problems of venting them properly. Even digging and pouring concrete piers would be difficult. I have found helical piles to be a suitable product. I've read several articles showing that they are easy to install and can support a cabin like mine no problem.
Jim, I was unaware of any "end of firing instructions" regarding being present until the last ember is out. In the winter if I set the fire when the sun goes down (at 5PM or so) it should be out by morning. If I am away for a few days the propane backup could be set to keep the place warm.
Malcolm, the shed design of the roof angles up to the north and their are two clerestory awning windows (which would be above the masonry heater) to help control indoor temperatures (and also provide a thermosyphon effect in summer). One west window in the living room and the east window in the bedroom will open as well.
Martin, I've been trying to find a solution to the pipes coming out of the ground and the best thing I can think of is to not put them in the ground. A short distance away from the cabin is going to be a converted refrigerated shipping container. This is going to house all the mechanicals (electrics on one side, water on the other separated by an interior wall). This can be on the ground. Since the floor of the cabin is on piers and will be made out of SIPs I don't want to come up through the SIP but rather through the side wall and under the false floor. I plan on building a SIP chase between the side of the cabin to the shipping container (the chase will be under the surface of a deck.. If I run any pipes within a conduit within the chase I could even spray foam around the pipet before I seal the chase.
I was wondering about how you provide your water, Martin?
In further consideration of isolating the kitchen from the rest of the cabin in order to contain propane cooking fumes I've come up with a variation on the cabin. The kitchen is now in an "east wing" that can be closed off by a pocket door and the entrance is now where the kitchen used to be. Moving the entrance from the west side also allows me to expand the screen porch a bit.
Martin, I was reading in an article entitled "Building an Energy Efficient Home on a Budget" that you recommended putting rigid foam on top of a SIP roof and then a cold roof above that. Wouldn't rigid insulation panels trap moisture that may leak through the seams (or get in under the rigid foam from rainfall)? I read that since SIPs have a very lower perm rating that any material applied to the outside of them should allow moisture to evaporate easily. That's why I am considering Roxul mineral boards for the SIP wall exterior but was wondering if they would be a good idea on top of the SIP roof panels too?
Scott,
Putting your pipes in a horizontal chase to a shipping container does not sound like a good idea.
First of all, horizontal drain pipes are far more likely to freeze solid than vertical drain pipes.
Second, do you anticipate making this horizontal chase capacious enough to have significant air circulation around the pipes? If so, how will you heat that air?
Chases like the one you describe exist in Alaska, but they always include a source of heat (either circulating hot water or an electrical-resistance wire).
Third, what keeps all of the plumbing pipes in your shipping container from freezing? Moving your vulnerable pipes out of a SIP house into a steel shipping container doesn't sound like a solution -- it sounds like a step towards increased problems.
At my house, my water supply comes from a natural spring located above my house. It flows by gravity to my basement. The pipe is buried in a trench that is between 36 inches and 42 inches deep.
My drain line goes to a septic tank and leach field. The drain line is also buried in a trench.
Scott -
If you build a fire in a masonry heater at 5 and don't shut it down until the following morning, you'll have been losing stored heat all night. I agree that masonry heaters are beautiful and in many ways the best way to heat with wood. I also think if you take cost out of the equation, you could look at the stats (efficiency, duration between loads, overall wood consumed) and feel like a masonry heater dominates a wood stove with no down side; this is not the case. If you want to store heat in a masonry stove and actually take advantage of their potential to hold heat, you need to babysit the end stages of your fire. If you aren't present at the end of the fire, air pathways remain open, and your stored heat goes out the chimney. If you don't keep your heater warm at all times, then the flip side of storage potential - response time - comes into play as a negative as well.
For the record, I hope you build a tulikivi and we get to see pictures of it. I'm just saying that any time you decide to make wood your primary heating fuel, you are going to have to pattern your life around it to some degree. Major masonry stove manufacturers like tulikivi have published operator's manuals. Check it out and make sure it will actually fit with your lifestyle.
Thanks Jim, I had a look at the Tulikivi operating manual. Once you find the English part (lol) it says that during the firing process the air control lever setting on the ash box door remains open during the ignition and firing , then is half closed when there are coals and then fully closed when they become dark coals. It doesn't say anything beyond that. if the model you have has a damper then at that point it is closed too. The total firing time is supposed to take about 2-3 hours so by the time you're going to bed you close it up and don't have to do anything. According to their brochure the stove is still emitting stored heat 15 hours later (at about 25% of its initial heat from the firing).
Martin, the other option is putting all the mechanicals into an insulated room in a garage and running the pipes underground. One place I could bring them up through would be inside the insulated concrete forms I would have to build to support the masonry stove. I have to dig down about 4 feet and pour a concrete pad anyway and then use those insulated concrete forms. I could fill the forms with sand and bring the pipes up inside and then under the false floor. Perhaps I could rig up an extra loop of pipe from the hot water attachment on the stove to go down into the middle of the support column to help heat the sand in winter.
As to the roof, do you think adding a 2" layer of Roxul Comfortboard to the exterior is worth it. I would put 2x4 furring strips on top of that and then the plywood and finish roofing.
Scott,
I've built a couple of houses on piers. I usually provide a small core to bring the services up from the ground. If you aren't using any concrete you could still build one by framing a box using ground contact PT lumber from the underside of the floor down to whatever the frost line in Nelson is (4'-0"?). Insulate the sides and bottom with foam and leave the top open to the cabin so as long as the building doesn't freeze, neither will the chase.
A small cabin near Nelson is a lot of people's dream.
Scott,
If you build a mechanical room in your garage, it will need a separate heater to keep the room from freezing, especially if the room includes plumbing. The ideal space for a mechanical room is inside your house.
Q. "Do you think adding a 2-inch layer of Roxul Comfortboard to the exterior is worth it?"
A. It's hard to know what you mean by "worth it." If you have a SIP roof, then additional insulation on the exterior of the SIPs is unlikely to be "worth it" if you are looking for energy savings that are large enough to provide a return on your investment -- especially if you are heating with wood, which may be free.
Malcolm,
If you have built off-grid homes in Scott's climate, and if the type of utility chase you describe keeps pipes from freezing, that's great. It certainly wouldn't work in Vermont, so I'll have to assume that minimum temperatures in your part of British Columbia are relatively mild.
Here in Vermont, where temperatures routinely drop to -20°F (-29°C), the air in the type of vertical chase you describe would freeze, and so would the pipes. Even if the room above the chase is heated, the heat won't drop down into the chase, because the stack effect depressurizes the air in the chase with respect to the heated air above. Tiny air leaks in the chase pull in outdoor air, and tiny air leaks in the cabin's ceiling allow heated air to escape. The stack effect defeats us, every time.
Are you sure that your memory serves you well? You are talking about an off-grid house, not a grid-connected house where the plumber installed electrical heat tape in the chase?
No Martin it had no additional source of heating, but as you say it was here in Lotus-land where we face at most a week of sub-freezing temperatures. I'll defer to your advice for more severe conditions - which probably includes Nelson.
Well, there must be a way to get pipes up from the ground and into an off grid cabin built on piers without the pipes freezing. I realize that slab on grade would be a much better option but what do people do when they don't have access to lots of concrete? I figure if I use a separate insulated utility space in a garage that the pipes can be underground from the well to the storage tank inside. Once above ground the water would be cleaned and treated before being stored. Then more pipes above ground to transfer the water to a heating device (either solar or propane) and then stored again in a heated tank. Probably a final pressure tank to get typical "city water pressure". Then back underground to the cabin. There must be a way to get it through the final 2 feet to inside the cabin without freezing.
I have no idea how much space all that equipment would take but I don't really want to add on another room just to house equipment. Then there's the issue of dealing with the water once it's been used. I'm going to have a composting toilet so I don't have to worry about that but I will have greywater . Whoever said moving to the country was "the simple life" should have been shot.
Scott,
You wrote, "There must be a way to get pipes up from the ground and into an off grid cabin built on piers without the pipes freezing."
Well, if you're convinced, be my guest. If someone is living in the cabin, and the cabin has a gasoline generator or a propane generator, you can always make enough electricity to keep the electric heat tape warm.
I built an off-grid house on piers. My plumbing froze. For one winter, I melted snow for water.
The next summer, I built a cellar under my house to keep the pipes from freezing.
Scott (and Martin),
I have to say that this has been a fun post to read (but re-reading it to try to figure out where we are at is starting to take significant time). My first house was on piers in Ottawa (routinely sub minus 30 in winter). The water pipes came in through a (poorly designed) unheated crawl space with the pipes boxed in and insulated similar to what Malcolm described - but a much more amateur version. There was no heating tape and the pipes never froze. One factor may have been the depth of snow cover, the other was that the house was well sealed (it was a continuous fiberglass shell) so there may not have been as much of a stack effect.
On a separate note - in reading through this I think that some of the comments are confusing a Tulikivi stove with a masonry heater - although both rely on thermal mass I think that the Tulikivi style is perhaps more like a normal woodstove (but I have no experience with either). In either case, you know that you have arrived when you run out of wood in the dead of winter and start eyeing the furniture for fuel potential :)
Rob (and Scott)
I think Martin may have dismissed the effectiveness of what I suggested partially because of my poor description. The service accesses I've built were more akin to a small crawlspace that chases. They were around 3 ft square, so that the area of exposed surface to the room above was larger than the two feet down to the grade. Unlike what I described to Scott, who doesn't have access to concrete, they sat on small stem walls extending below grade, but I don't think this is materially different to a completely wood foundation.
What might make it difficult in Scott's case is that the cabin is so small it would be difficult to find sufficient floor space in the plan to devote to such a chase. In the houses I used them in they were part of the floor in a utility room.
What drew me to using them was that they don't rely on a dedicated heat source. As long as the house stays heated, the crawlspace/chase does too.
Scott,
I'm happy to concede that there may be a solution that doesn't involve concrete. I just want Scott to be fully aware of the risk of freezing his pipes before he chooses his foundation type (and the location of the mechanical room).
In Comment #48, Scott repeated his idea of bringing his water pipes into "a separate insulated utility space in a garage." So where does this room get its heat? Does it share a common wall with the house? (I don't see it on the plan.) If so, is the common wall made of louvers to allow the free flow of air between these two spaces? If the room is in a detached garage, it will, of course, need a wall-mounted propane heater. And you're still stuck with the problem of bringing the pipes into a house on piers.
Concerning the solution I adopted (retrofitting a cellar under an existing house on piers so I didn't have to spend the rest of my life melting snow on the wood stove): It's important to mention that this cellar doesn't have to be a full foundation. The one I built for the house on piers is a basement measuring 8' x 8' x 8'. To work, this type of basement needs to be deep (to take advantage of the warmth of the earth) and as airtight as you can make it.
Finally, if we adopt solutions that depend on lots of snow as insulation, we may be surprised by a low-snowfall season. That's happened in Vermont, where some people bury their pipes in a 24" or 30" deep trench. This approach works fine if snowfall is normal. Then (global climate change?) we get a winter with very little snow, and the pipes freeze.
Thanks everyone for your suggestions.
What I've been trying to do in using an old insulated shipping container for the utilities is avoid having to build any kind of basement. Without access to a ready supply of concrete the most I could probably manage on my own would be the small 3 x 5 footing pad to support the masonry heater and some ICF walls on top of the pad up to the underside of the cabins SIP floor. If I really insulate the chase well and dig the pad down to below the frost line I could get away with having the pipes come through an underground conduit. I suppose I will have to use electrical heat tape as well. Running a hot water loop into the chase may just complicate things.
I did find a soapstone heater called "The Vermont Bun Baker" that is rated for an area from 750-1000 sq feet and also includes a small bake oven and a hot water circulator. I'm assuming the "Bun Baker" refers to bread. :)
I know nothing about electricity but came across this interesting heating product. Would it work for an off grid home? The electrical information is under "Specifications".
http://wellconnectgeo.com/
Scott,
The link you provided describes a ground-source heat pump that pulls heat from water in a drilled well. This is a heating system that uses electricity for a fuel. It can't be used for an off-grid home, for the same reason that you can't use an air-source heat pump: you won't have enough PV electricity to run the equipment during the cold winter months.
If you install a ground-source heat pump, you'll end up running a gasoline-powered generator or a propane-fired generator to provide the electricity -- and it's more efficient to just burn the propane directly in a propane space heater.
Scott -
Field stone and spray foam can make a basement plenty tight to run utilities. Just throwing it out there as a possible solution to your lack of access to concrete. 6'x6'x6' may be all you need, and a nice size to learn on.
I remember looking at the Vermont Bun Baker. I think it is a metal wood stove and convection oven with a soapstone housing that it slides into. Check out hearthstone stoves as well if you like soapstone. They aren't custom built masonry heaters...but beautiful stoves in my opinion.
Scott,
I'm still a bit unclear as to why concrete is out as a foundation material. Both SIPs and helical piers require a truck to get to the site and install. Concrete can be either pumped or moved in the bucket of a skid steer from where a truck can get access to. Is there some other reason you don't want to pour a foundation?
Scott,
As a followup to Malcolm's point: If you have delivery by truck, you could also consider using concrete blocks (CMUs).
Frank Lloyd Wright used a foundation in which limited the use of cement. It's based on how railroad tracks work and his buildings are solid. You dig past your frost line, replace the dirt with gravel and use a cement beam on the surface of gravel. You build on the beam. Not sure if this type of foundation works for you, but it limits the amount of cement that you need and even less cement/insulation than a shallow poured cement foundation that relies of insulation instead of gravel.
Pier foundations are fine to use as well. You can use insulated skirting on perimeter without it being structural to the building. Probably the easiest solution to your issues. You can further insulated between the joist with rockwool.
If you want to heat a utility chase in an offgrid home, you could insulate it well (say R30), run a loop of pex up and down it and attach a 5W circulator, thermostat and an air->water heat exchanger at the top. At -20F, it should run about 1/3 of the time (and that's not accounting for any heat from the other pipes) . So 40 Wh per day, worse case. You need some heat, but very little.
A rubble trench. But I'd say that foam insulation (ie a frost protected shallow foundation) is easier for one person to manage than lots of gravel. The amount of concrete should be the same.
The site is quite remote so I've been told that a large concrete truck couldn't get in there. I also don't want to get into the hassles of digging for perimeter foundation walls, insulating them, installing drainage and all the other problems involved in putting in a basement or crawlspace.
As to the possibility of using a slab I have found a product from Legalett where you can build a Geo Passive slab with very little groundwork needed (certainly a lot less than putting in footings below frost depth). I've sent them an email asking for more information and included a dimension plan to get a quote. Whether or not this results in a viable solution remains to be seen.
The person putting in the helical piles says that all he needs is a small bobcat type of machine in order to install the piers. I'm also trying to design the cabin so that the SIP panels are small enough for 4 people to lift rather than using a crane. Placing the floor and wall panels should be no trouble but the 4x12 roof panels will weigh about 400 lbs each so we'll have to use a forklift.
Hi, Martin. After looking around on the "small cabin forum" I saw mention of a product called the "Panasonic WhisperComfort Spot ERV Ceiling Insert Ventilator".
http://shop.panasonic.com/support-only/FV-04VE1.html
I was wondering whether you thought this would be a better option than the WhisperGreen fans or the Lunos fans?
Scott,
The main reason that the Panasonic Whisper Comfort ERV has limited applications is that it can't be used during the winter in a cold climate. See the map below. If you live in Region C in British Columbia, the Panasonic ERV can only be used from April to November. It won't work in December, January, February, or March.
.
I'm beginning to understand the perverse joy in trying to design and build a small cabin. Every decision results in 10 more decisions. I also realize that I HATE wood stoves. To me they take up far too much space and for 6 months out of the year they just sit there idle. When you finally find a wood stove that won't roast you alive inside your tightly sealed building its small size makes it impossible to use for anything else like water heating.
SO! No wood stove. I think the best solution is an indoor furnace in a small outbuilding with underground pipes to the cabin for DHW and baseboard radiators in the winter. In the summer there's going to be solar hot water and that's that.
Martin, I've read in several of your posts that you recommend not using an outdoor furnace because they are very inefficient and also very polluting. I was wondering what you thought of the newer indoor and outdoor furnaces that are designed to comply with the most recent emission laws?
The model I'm looking at is the Econoburn 100.
http://econoburn.ca/index.php/en/products/interior-ebw-100
Do the newer generation of outdoors wood furnaces change your mind about them?
Scott,
The newer indoor wood boilers are great for the right application - but the Econoburn is 100,000 BTU's - much too large for what you need. Adding radiant heaters, underground piping and circulators/controllers is making for a complicated system that requires significant power to run. A wood stove is probably the least expensive and most viable option. It does not have to be ugly or take up a lot of space. There are small stoves with controllable heat outputs and very small rear clearances. With a proper rear heat shield and floor protection they are pretty unobtrusive and do not take up much space at all. And in summer you can use them for a plant stand (and I'm only half kidding). With off-grid - simple is better.
Scott,
You are over-thinking this. The size of your cabin is its great asset, not a problem. A well insulated and sealed building of the size you are proposing needs such a small amount of heat you can use any simple source - and can afford to be inefficient about it without incurring any significant penalty. Put in a very small wood stove. If it gets too hot, open the window. The additional wood you "waste" will be negligible.
Scott,
Rob and Malcolm gave you good advice.
What you call an "outdoor furnace" is more properly called an outdoor boiler. I know a young family in Vermont (the mom was my son's middle-school science teacher) who built an off-grid house without doing much research. They installed an expensive wood-burning outdoor boiler to provide space heat. The first winter, the boiler immediately drained their batteries (because it required an electric circulator and electric controls). They spent the rest of the winter operating their gasoline-powered generator almost all the time, simply to be sure they had space heat, and the cost of the gasoline and the noise of the generator almost bankrupted them and almost drove them to divorce court. The next winter, they used a wood stove.
As I advised you in one of my earlier comments, if you live in an off-grid house, it is essential to choose a space-heating appliance that does not require electricity. Your two choices are a wood stove or a propane space heater with a through-the-wall vent.
Thanks everyone for your advice. The irony in designing this cabin is that as technology and building practices have improved the choices for providing space heating and DHW have grown far more complicated. In the old days you just went out and built a drafty, barely insulated shell and put in a smoky wood stove and didn't worry about anything. Now buildings are so tight it's recommended that you shouldn't have a wood stove inside them at all. Just cooking can fill the interior with unsafe levels of contaminates.
The two wood stoves I've looked at are the "Aspen" by Vermont Castings and the "Bunbaker 1200" by Vermont Soapstone. I prefer the soapstone stove because I think the stone will help even out the temperature fluctuations, you can cook in it and you can also get a water coil included. If you're going to have a fire you might as well get hot water in the winter too. I also plan to include an Empyre propane heater (since I will also be using propane for cooking anyway) and the Lunos fans for ventilation. There's the kitchen vent hood and the WhisperGreen fan in the bathroom.
During the summer I think those evacuated tube hot water heaters are probably the best solution.
Contrary to appearances, I am actually listening to everyone's advice.
Scott,
We're up to Comment #69. Way back at Comment #1, which I posted on Oct. 22, I wrote, "Since your cabin is off-grid, you really only have two options, in my opinion. You can heat your cabin with a wood stove. Or you can heat your cabin with a propane-fired space heater with through-the-wall venting. (Be sure to choose a model that doesn't require electricity to operate.)"
If some of us wonder whether it's true that you "actually listening to everyone's advice," it may be because, in Comment #65, you told us that you will be using a heating appliance that (in Comment #1) I advised you to avoid.
Touche. in rereading comment number one you did indeed advise me against using a solar thermal or solar pv system to heat the cabin. I understand that. I'm now trying to find a way to heat the cabin without using a wood stove that is so powerful I have to open windows to get rid of the waste heat AND also find a way to heat DHW.
Small metal wood stoves can provide the space heating function but not hot water. Indoor boilers can provide both but the system is complicated and expensive and needs electricity to operate. Evacuated solar tubes would provide plenty of hot water in the summer (when a fire wouldn't be needed or wanted) but in the winter you'd have to have some kind of back up system. Propane? Water coil in the wood stove?
An Aspen wood stove by Vermont Castings is rated at 28,500 BTU's per hour. The Vermont Bunbaker 1200 is rated at 30,000 BTU's per hour but has 2 3/8 inches of soapstone around it to store the heat and radiate it throughout the day. Is that too much heat for space eating the cabin? Is it able to provide enough winter time hot water?
As I go back and forth between all these different systems and options it gets confusing. Whenever I find a possible solution it seems the electrical requirements rule it out. Just because it may take me 69 comments to narrow down my choices doesn't mean that I'm not learning.
Scott,
While anyone who lives with a wood stove quickly learns how they work, it's possible that you don't really understand how they work. At the risk of stating the obvious: just because a stove is rated at 30,000 BTU/h, doesn't mean that you need to start a roaring fire if you don't need one.
If you wake up one morning and the house is a little chilly, start a little fire. Let's call it a 5,000 BTU/h fire. A wad of newspaper, a few twigs, and two or three of the smallest pieces of wood from your firewood box. If you know what you're doing, you won't start a 30,000 BTU/h fire that forces you to open the windows on a cool morning in October.
For hot water, I have a solar thermal system for summer, and a thermosiphon loop on my wood stove for the winter. These two systems are supplemented by a propane-fired tankless water heater for backup. To keep things simple, there is nothing wrong with just installing the propane water heater -- it will take care of your needs easily, and it doesn't take up much room.
If you want to reduce the use of propane to a minimum, buy a wood-fired water heater. (Here is a link to one available from Lehman's.) Good friends of mine used a water heater like this for years, summer and winter. Right before you want to take a shower or bath, you light a fire in the firebox.
If you want to live off grid, life isn't necessarily complicated. You just have to choose the right tools and appliances. I don't think these choices are as confusing as you maintain -- you just need to listen to a few people who already live off grid.
Thank you Martin, that is practical advice. In reading articles about wood stoves I have seen it stated time and again that small fires are to be avoided since they can be smoky and cause creosote to build up in the chimney.
I had no idea that a "wood fired water heater" was available. I assumed that that was what I was looking at when I was considering a wood fired boiler.
These are the types of products that I wish you would write about in how to set up a modern off grid home. Everyone talks about what's needed for Passive House standards and Net Zero standards but nobody writes about completely off grid needs.
Scott,
As I wrote before, there are many resources for off-grid homeowners. One of the best is the catalog published by Backwoods Solar Electric. It's free.
I'm running out of wall space to put the propane heater. Every spot on the main floor is too close to something. I was wondering if I can put it up on a ledge at loft height (9 feet off the floor and about 2 feet under the cathedral ceiling). Would that really prevent too much heat from reaching the floor below or would putting it up there even be allowed by code?
Scott,
The clearances required by the manufacturer of the Empire DV-210-7SG heater are shown in the image below. On the interior, it looks like you need at least 12 inches from the top of the unit to the ceiling, and on the exterior, it looks like you need at least 16 inches from the center of the vent to the soffit.
That said, my advice to you is to install the unit normally, with the bottom of the unit a few inches off the floor. If you follow my advice, you'll be much less likely to have temperature stratification problems.
You are now at the design stage of your project. I assume that you still have plenty of time to make adjustments to your design to include a heating system. Every house in a cold climate needs a heating system, and every heating system requires some floor space. It's hard to imagine any heating system that requires less floor space than a wall-hung propane-fired heater. The heater will take up less room in your house than a wood stove or a forced-air furnace, so you should be able to accommodate it with a little planning.
.
Scott,
I'm not sure if you will ever check in on this very long Q&A thread that documents your series of questions about designing an off-grid house. But in case you do, I thought I would respond to what you wrote in Comment #23: "Perhaps, as I suggested, you could write those blogs about what you would do if you were starting out today to build your off-grid life using today's products and construction methods. I really would like to learn from your mistakes."
I've written the article you suggested. Here is a link to the article: How to Design an Off-Grid House.