Image Credit: Erica Breetoe
More Musings of an Energy Nerd
If you’ve been heating your house with wood for years, you probably don’t need to read this article. By now, you know all about the disadvantages and inconveniences that accompany wood heat, and yet you still heat with wood — either because you genuinely love wood heat, or because you love the low cost of the fuel. If you haven’t burned down your house by now, you may even have figured out how to install and operate your stove safely.
This article is addressed to a different audience: those who are thinking about buying their first wood stove.
Forget about the warm glow — and get ready for lots of schlepping
For some homeowners, especially those who haven’t lived with a wood stove, wood heat has romantic associations. Veteran wood burners know better, however. As a document from the Cornell University Cooperative Extension points out, firewood “is one of the least convenient sources of heat, … requiring time and considerable effort to fell and split trees, move wood into dry outdoor storage for at least a year, transport wood indoors, maintain an effective woodstove fire, and keep the system cleaned for safety and efficiency.” I’ll add another disadvantage: if you heat with wood, you’ll be tethered to your house all winter. You won’t be able to go away for the weekend unless your house has a backup heating system to keep your plumbing pipes from freezing.
Wood heat makes the most sense for:
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57 Comments
Any experience with Masonry heaters?
I am considering installing a small modular masonry heater/ bake oven in the home I am planning, probably one from Eco-firebox in Maine. (http://ecofirebox.org) It seems like way they work would be better for a super tight building than a traditional woodstove. A small hot fire in a huge pile of masonry that very slowly releases its heat for hours after the burn. I know they are not cheap, it's definitely an aesthetic thing, but I was also thinking that all that masonry will function as thermal mass from a passive solar perspective as well, as long as I place it in direct sunlight. Are you aware of any use of these in high efficiency homes?
Response to Eric Peterson
Eric,
Some of the issues surrounding your question were discussed in a GBA article, Are Masonry Heaters a Good Match for Superinsulated Houses?
Here are my comments: a masonry heater is a good way to heat a leaky, poorly insulated building. Masonry heaters have at least three big drawbacks: They cost an arm and a leg. They take up a lot of room. And during cold weather, they require the homeowner to kindle a fire from scratch twice a day.
There is a standard piece of advice that I give to anyone who is contemplating the purchase of any expensive heating equipment: why not take the money that you would have spent on the expensive masonry heater, and spend it instead on air sealing details, better insulation, and better windows?
If you improve your thermal envelope, you won't need such a big heating system.
You may still be able to
You may still be able to leave for the weekend if the house temp won't drop too low with no fire. Perhaps it is built well enough that the plumbing will not drop below freezing, ever, and the stove is used for comfort rather than freeze prevention.
I would like to emphasize the importance of hot fires. I used to clean my chimney yearly, but after the first few years learned that starting a fire fast and hot, using nice dry wood, and never restricting air before only coals remain leaves me with a pristine chimney. I still check it though...
I agree, though: it is better to build well and not to need to burn the stuff at all, for lots of reasons.
I like masonry..
Thanks for the reminder about that article. It's worth re-reading.
I'm aware of the cost and I wouldn't be exchanging a good envelope for a masonry heater. I'm a carpenter by trade and a half decent mason, so I could and in fact want to, do a lot of the finishing myself. One of the alternatives that is mentioned a couple of times in that article, the Vermont Bun Baker, approaches $7k if you go for the version with the most soapstone, so that's hardly a budget choice either.
I took Marc Rosenbaum's net zero class this spring and he mentioned that he would be using both a wood stove and mini-splits in his next project, with the idea that the mini-splits operate less efficiently at really cold temps, and the woodstove is a hassle during the shoulder seasons, so the two systems would complement each other well.
Like I said, a big part of this is the aesthetic and the desire to do the work. I am prepared to accept that I may be bull-headedly pursuing an irrational and purely aesthetic goal, but I am curious if anyone else has done a similar thing and what their experience was.
Response to Dustin Harris
Dustin,
If you are lucky enough to live in a very tight, superinsulated house -- or a mild climate -- you're quite right about leaving the house unheated for a few days, even in January.
Alas, my house doesn't fall into that category. If I leave the house in January, when the temperature can drop to -30°F, my house is neither tight enough nor well enough insulated to keep my pipes from freezing. So I have to light a propane space heater when I leave in the winter.
You're also correct that hot fires and much better than smoldering fires. Hot fires keep your flue clean -- just as a vegetarian diet keeps your arteries clean. It's still a good idea to inspect your flue annually, however.
Thorough...
Martin,
Though I don't consider myself an expert on this subject, I do have some experience and I found your article to be very comprehensive.
A couple of minor things I thought of while reading:
Old pallets make a great surface to stack your firewood on.
Where I live, a person will save the most money by buying cordwood in 8' logs.
Last year, birch (the best common firewood in this area) in 8' logs went for $100/cord and when split went for $300/cord.
When shopping for firewood, try to buy from someone who hasn't skidded the logs through a swamp or mucky clay - firewood that is excessively caked in dirt and mud sucks.
Response to Lucas Durand
Lucas,
I haven't heard of 8-foot firewood logs. Here, the people who want to save money buy "tree-length" logs right off the logging truck. The logging truck comes straight from the woods to your dooryard.
Muddy logs will dull your chainsaw quickly. So buy your tree-length logs in mid-winter, when the logs have been skidded on snow.
Response to Kevin
Kevin,
At least once a year, it seems, there is an article in a local Vermont newspaper about a rental house fire. The newspaper stories usually include this sentence or one very much like it: "Fire investigators determined that the fire started when the tenants removed ashes from the wood stove, put the ashes in a cardboard box, and placed the box on the porch."
Bad Experience in Montezuma, CO
Woodstoves are ubiquitous in the mountains of Colorado. One particular landlord in the area has had three homes burn down because his renters were ignorant of the maintenance and safety issues in regard to wood stoves.
http://www.summitdaily.com/news/5137494-113/leadstories-localivg-leadstoriesivg-apaccidentsanddisasters
http://www.summitdaily.com/news/6321452-113/columns-leadstories-columnsivg-leadstoriesivg
http://www.summitdaily.com/news/5136518-113/regional-leadstories-regionalivg-leadstoriesivg
Excellent Advice
Great blog as usual. One regional difference out here in the PNW: Firewood suppliers don't worry about the load capacity of their pickup trucks. They wedge a small log into the leaf springs and hope for the best. I know as I follow them from the cut blocks around me hoping they make it to their clients in one piece while spilling rounds on the way.
My house is superinsulated
My house is superinsulated and very tight (last blower door test gave 0.8 ACH/50). It has a small woodstove on the lower level, with a firing range of 11-28,000 BTU/hr, according to the tag that was on it. The heat loss model for the house showed a design heat loss of 22,000 BTU/hr. The house is big enough that for the 4-6 hours we sometimes use the stove, starting around supper time, we don't get what you'd call overheating. The house seems to absorb the heat easily for that duration.
I like to burn a medium sized but hot fire, with no noticeable smoke from the chimney. The stove has a ducted outside air source connected directly to the back of the stove. I have to be careful when lighting off the fire, making sure that neither the clothes dryer nor range hood is operating then, or I get downdrafting, with smoke leakage past the stove door gasket. Once the stove is burning well and drawing smoothly from the outside air duct, the clothes dryer or range hood can be used. However, using the range hood on the highest setting without opening a window nearby can be problematic.
burning soft wood
Martin,
Thank you, great read as always.
However on one point I am going to disagree and that is on burning soft woods and resins and creosote build up. That one is a very (very) common myth.
Creosote build up is a moisture issue - burn wet wood or burn cold and you get creosote build up - burn dry wood and burn hot and you don't get creosote build up - apples to apples comparison between hard woods and soft and there is little to no difference between one or the other pertaining to creosote build up.
Keeping in mind the other points that you mentioned such as warm chimney, etc. which potentially do have a significant effect on creosote build up - much more so than wood choice.
But why?
Hi All,
I've read many times that fire places draw heat from the house, but I've never gotten an explanation for WHY that's more true for a fire place than a wood stove. Certainly the same forces must be at play. What's the difference? Is it absolute or is it also a matter of how one adjusts something?
J.
Fireplace vs woodstove
While a fireplace may heat the area immediately around it, by radiation, an open hearth and wide open flue draw a huge amount of excess room air and send it up the chimney. That air must come in through the myriad leakage points throughout the house, making chilling the rooms away from where the fireplace is located. Further, if the thermostat for the heating system is in the vicinity of the fireplace, the thermostat may remain satisfied while the rest of the house is much too cool for comfort.
A woodstove, with its door latched, draws just enough air for efficient combustion. For a small woodstove, this may be only 40-50 cfm, well within the potential leakage rate of even a very tight house. That's why a woodstove actually can work in a tight house without an outside air source. Still, I would advocate having the outside air duct, to nearly eliminate draw of inside air up the chimney at times when the stove is not in use, and particularly when the fire has burned out for the night. Of course, if the firebox is loaded for an overnight burn, this is not an issue.
Response to Greg Smith
Greg,
Thanks for your comment. I am always willing to learn and acknowledge my mistakes. Do you have any references to published documents backing up your statement about softwood fuel and creosote?
Response to Jason Crawford (Comment #13)
Jason,
Dick Russell's explanation is correct. Here's another factor: while a fireplace fire heats nearby objects and people by radiation, the fire mostly heats air that is in the fireplace -- air that is on its way up the flue. A stove fire, on the other hand, heats the steel or cast iron which surrounds it -- and that steel or cast iron is located in the room, not in a flue. So the hot steel helps heat the house.
Martin,I suspect that there
Martin,
I suspect that there has to be some sort of definitive document hidden somewhere in cyber-land, but if there is, I couldn't find it.
I did find a fair bit of anecdotal information on various chat sites and a few articles addressing the issue. Nothing conclusive from a recognized authority though.
This is about the best I could find:
http://www.superiorchronicle.com/archives/08_september/chimney02.html
http://chimneysweeponline.com/hosoftwood.htm
http://www.motherearthnews.com/homesteading-and-livestock/ask-our-experts-wood-burning-stove-creosote-buildup-zm0z11zblon.aspx
Response to Greg Smith
Greg,
Thanks for those links. I appreciate the information, and I have edited my article.
why I do it
I’ve been heating with wood since 1984, so I fall into the class of people who “ may even have figured out how to install and operate your stove safely.” I agree with you cutting and splitting wood is time consuming, and I realized early on that if I wanted to heat with wood, I’d have to buy it cut and split, which I do ( I work for a living and had to compromise)
My house meets two of the qualities listed for homes where wood heat makes sense
• Compact two-story homes rather than stretched-out single-story homes;
• Homes with an open floor plan rather than homes with many small rooms and many closed doors.
The reason why I first used wood, besides early poverty of the ex grad student, was that the electric in my area was not reliable. It was necessary to have a source of heat that would last through the mid winter storms. This is now not as big a problem as it used to be.
I recently upgraded to a wood stock progress hybrid soapstone stove, a beautiful device to look at as well as to use(1). It’s hybrid because it uses both a catalytic device, and secondary heated air combustion. The particulate emission rate is 1.33 gm /hr (2). Measured efficiency is 81%. The progress hybrid even has an outside air intake, for sealed combustion use in a motor home, though in my opinion, you’d need a pretty big motor home. The biggest quality is that a soapstone stove heats up slowly, and releases the heat over several hours compared to a cast iron or steel stove (which heat up quickly and go cold quickly). Hearthstone site has a good graphic on this quality(3).
For the weekend problem , when I’m not there to stoke it, I now use a Fujitsu RLS2 split duct heat pump, before the heat pump I used a propane wall heater back up. FWIIW, I have solar panels on the roof and am a net energy generator, which I intend to someday burn up in the heat pump, but not just yet because I like wood heat. I use microinverter grid tied solar panels because there are no moving parts. The SREC credits more than pay for the wood
As to Martin’s question ” why not take the money that you would have spent on the expensive masonry heater, and spend it instead on air sealing details, better insulation, and better windows?” my answer is that because it is boring and dull. That , and I really do not want to tear apart my house, I want to live in it. I want to live in a house full of light and heat and fresh air. Sometimes I leave the windows open in dead of January so that I toast myself on the wood stove side, and cool on the window side. It’s fun, even though das ist verbotten to the air leak fearing heat calorie counting passiv haus aesthetes.
There is an aesthetic element, present company excluded, that the passive haus devotees seems to miss. At the limit, it seems this crowd, again present company excluded, want folks to live in a windowless foam box, with a double sealed air lock suitable for immersion to 30 m depth, with only a heat exchanging snorkel to allow fresh air to enter, preferably heated with the glow of a 2 watt led bulb
A wood stove is a thing of beauty, and the winter rhythms of tending to it are a joy.
That’s why I do it
(1)http://www.woodstove.com/progress-hybrid
(2) http://www.epa.gov/oecaerth/resources/publications/monitoring/caa/woodstoves/certifi (3)http://www.hearthstonestoves.com/customer-resources/Why-soapstoneedwood.pdf
"A wood stove is a thing of beauty, and the winter rhythms of tending to it are a joy."
Not to be forgotten!
Fireplace Boiler Combos
There are three factors that are required to achieve successful fire in a low ACH house.
-A sealed OAK (outdoor air kit) to the manifold, and by sealed not a just a duct to the general area
-Keeping the dryer and range vent off when the door is open to prevent backdraft
-Minimizing wood stove fire output. Unfortunately the days of McMansions has lead to a lot of the attractive units with outputs of 40-80k btu, which is way to much output. There are number of new companies integrating water jackets above fireboxes which will allow for a 30%/70% split storing additional thermal energy in water for use in hydro air setups or DHW.
Response to Martin Holladay
You are more than welcome.
Masonry Heaters and softwood
I agree with Martin that good design, air sealing and insulation trump expensive heating systems. Masonry Heaters are expensive compared to a nice EPA certified Phase 2 Parlor stove. Generally speaking fuel efficiency and emissions are somewhat better for Masonry Heaters but not enough to justify the added cost. Masonry Heaters do have some qualities which distinguish them from steel or iron parlor stoves. They allow high temperature combustion fires (including softwood) without causing overheating of the house because the structure of a Masonry Heater is a thermal battery with relatively low output radiant panels, typical heater output is around 20,000 BTUs an Hour. This actually is a reasonable output for an efficient home many freestanding stoves are rated at 40-60,000 BTUs an hour which can cause homeowners to choose a strategy of small restricted burns in an effort to avoid overheating. This can lead to high emissions, and creosote condensing in the chimney. The footprint of a masonry heater is actually pretty similar to the footprint of many other wood burning devices if the clearance to combustibles required for steel or iron stoves is accounted for. Finally if a homeowner is willing to pay for a classic masonry hearth Masonry Heaters allow that with performance as good or better then almost any other cordwood (or pellet) burning device.
masonry heater emission and efficiency
I was curious about the emission rates of masonry heaters. Particulate emissions for Masonry heaters are listed in gm/kg, and wood stoves in gm/hr
Turns out, it’s hard to compare because they operate differently:
“Moreover, the very different operating profiles for masonry heaters compared to woodstoves present difficult issues when attempting to make "equivalency" findings. The fuel load in a masonry heater is fully-consumed in a short period of time. This heats a large mass of refractory, which in turn discharges the stored heat over many hours. Woodstoves are also batch loaded, but the heat is delivered as the fuel load is consumed. The length of the burn depends on how the operator sets the air controls. When comparing emissions performance on a gram/hr basis, the masonry heater emissions must be averaged over the period of time that useful heat is being provided to the home in order to compare them with woodstoves on an "apples to apples" basis.
http://static.hpba.org/fileadmin/Govt._Affairs/MHWhitePaper13Feb08.pdf
Fig 4 on p 18 of this document comes closest to a comparison.. the grundofen beats out the phase 2 epa wood stove on a gm/hr basis
The other issue is efficiency : masonry heaters are in the 60% category, and best EPA wood stoves in the 80% range.. this is reasonably important if you are hauling wood
But.. the best way to improve the system efficiency is to lower the heat loss through the walls.. which I believe is Martin’s main point
Seismic
Another consideration for those living in the PNW or other active seismic zones when choosing to install either a masonry heater or chimney is their performance in an earthquake. I have seen a Finnish heater reduced to a pile of soapstone by rock blasting on a neighbour's lot.
Combustion air volumes (reponse to Dick Russell, in post #14)
Dick Russell writes:
"For a small woodstove, this may be only 40-50 cfm, well within the potential leakage rate of even a very tight house."
Combustion air flows of 40-50cfm not a small wood stove, that's a MONSTER woodstove (or a small open hearth fireplace.) At the small end the max combustion air flow rates for a sub-30,000BTU/hr stove will be ~10cfm, and throttled back it'll be 3-5cfm. A 150,000BTU/hr behemoth might draw as much as 25cfm or even a bit more at max-fire, but not more than 10-15cfm average.
But the basic point is correct- an open hearth fireplace pulls orders of magnitude more infiltration air than a wood stove, and even a fairly tight house has enough air leakage to supply combustion air for small woodstoves, as long as there isn't active exhaust venting in progress. A house that tests at a fairly low 500cfm/50 has the leakage equivalent of a 3.5" diameter hole in the wall, which is bigger than the dedicated combustion air duct for a substantial sized woodstove, but smaller than a clothes dryer duct.
And the rationale behind dedicated combustion air piped directly to the woodstove is the backdrafting potential under active exhaust venting in tight houses. A combustion air duct that only comes NEAR the woodstove rather than directly hooked up to it in a nearly air-tight manner needs to be able to handle more than just the 10-25cfm the wood stove needs, but also the homes combined exhaust venting volume to reliably achieve that end. Even then, wind pressures can sometimes reverse the flow in the flue, but as long as the combustion air is ducted directly to the woodstove and not the house, the flue gas (and potential embers) go out the combustion air duct rather than into the house. (Combustion air ducts need clearances to combustibles for exactly this reason.) It's difficult to make the wood stove, combustion air duct, & flue all completely air-tight, but in tighter homes it's definitely worth given it some attention when installing wood burning stoves.
Outdoor air supplies and woodstoves
Martin,
CMHC undertook several studies on woodstoves and spillage. They are probably archived now but I can dig them up if you want the specifics. What we do know is this:
- Outdoor air supplies will reduce the amount of indoor air used by the woodstove (but they may affect the woodstove efficiency in cold weather - I do not have data on this tradeoff)
- The ducting for outdoor air supplies must be designed to tolerate backdrafting, because they likely will. Think of your outdoor air supply as a horizontal flue pipe in terms of clearance to combustibles.
- Your woodstove will rarely if ever backdraft or spill during the main burn. At that time the chimney is developing so much draft, or woodstove depressurization, that it is far beyond whatever depressurization you create in your house. We have measured up to 50 Pa of draft. At the fire die-down stage (often in the middle of the night), there is little heat left to create draft but there is still good CO production. Spillage is possible then. Protect yourself with CO and smoke alarms.
- An outdoor air supply does not eliminate spillage. The pressures in the house and stove can still create a positive pressure to the house. We have measured this. When spillage happens, the relative tightness of the door closure or air openings are what will determine how much spills into the house. In an open fireplace, this could be all the combustion gases. In a tight woodstove, or a fireplace with tight doors, the spillage will be reduced but not eliminated.
- In tight houses with relatively neutral pressures (e.g. no large exhaust appliances), a small woodstove should be able to operate fine without an outdoor air supply.
I agree that the woodheat.org website is full of good information. Many of the research projects CMHC undertook had John Gulland as a contractor or advisor.
Don
insurance
One other thing to consider when selecting a wood stove is what your insurance company will allow.
Firewood seasoning --- a couple of points
1) Drying takes place almost exclusively through the end-grain so splitting logs does not make them dry faster
2) Moisture content is close to minimized after only 4 months. No need to season for 1 to 2 years
There are a couple of very good and very technical papers on the subject but it is worth noting that the information posted in this blog may be misleading.
Reply to Josh Wimpey
Josh,
The speed that firewood dries is highly dependent on your climate. While green firewood may dry in 4 months in Arizona, it certainly won't in the rainier parts of Oregon, Alaska, or Vermont.
There's also the question of "which 4 months?" You'll see more drying during June through September than December through March.
Martin, thanks for a very
Martin, thanks for a very timely article. I've been researching woodstoves for a few weeks, hoping to buy one soon. In addition to the lists at http://www.epa.gov/Compliance/resources/publications/monitoring/caa/woodstoves/certifiedwood.pdf and http://www.ecy.wa.gov/programs/air/indoor_woodsmoke/pdfs/Wood_stoves.pdf , you might want to share with readers the attached sortable spreadsheet my brother got from Larry Brockman at EPA.
2 questions:
1. Under what circumstances would you choose triple wall rather than double wall chimney pipe?
2. Are there any stove brands that are considered the "Honda" or "Toyota" of stoves? That is, high value brands that combine quality (efficiency, reliability and durability) with low prices?
In a solar wood kiln...
... it doesn't much matter- any four months will do, as long as you're far enough south of the arctic circle.
Stacked in the field and buried in the snow from December-March is a bit less optimal... ;-)
Even stacked in an open shed (still out of the rain) there's no way freshly cut green wood becomes wood-stove-ready in any four months in New England. Cut down dead trees or deadfall, maybe. Drying rates are a function of the wood temperature, and the relative humidity & air velocity of the proximate air. A reasonably designed passive-solar wood kiln improves all three.
Species also matters. (Cottonwood, anyone? :-) )
Another reply to Josh Wimpey
Josh,
I also disagree with you claim that "splitting logs does not make them dry faster." Try this experiment: cut down a 16-inch-diameter yellow birch tree. Cut two 24-inch-long pieces of firewood from the trunk. Split one chunk of yellow birch into 16 pieces, and leave the other one unsplit, with its tight green bark. After three months of drying, tell me whether your 16-inch-diameter round piece is as dry as my 16-inch split pieces.
George wrote, "The other
George wrote, "The other issue is efficiency : masonry heaters are in the 60% category, and best EPA wood stoves in the 80% range.. this is reasonably important if you are hauling wood." I'm told that evaluating both masonry heater and stove efficiency is a slippery subject. Where are you getting these numbers, and why do you trust them?
Masonry Heater efficiency...
Masonry heater manufactures and advocates claim 80% as well, I've not seen the 60% number before.
blueberries
Martin wrote, "Never put wood ashes near blueberries, since blueberries prefer acidic soil." Here in Georgia that advice also applies to azaleas and sometimes hydrangeas.
One thing I can agree with is
One thing I can agree with is the assertion that city people probably shouldn't own wood stoves. All this malarkey about inconvenience and having to cut the fuel and so on is about what I'd expect from them. They are about as clueless about such things as I am about why anyone would live amongst so many people that you can smell them as you come into town.
But an old fashioned wood stove isn't what a self-described "energy nerd" should be wasting his time on, anyway. Why not do an actual, real-life evaluation of a rocket stove? Those fascinate me and I'm thinking of building one into an attached "porch" and circulating that heat into my house through some probably non-approved through-wall vents - one high and one low to allow gravity to do the work for me.
Response to Brian Godfrey
Brian,
Once you've built your contraption and lived with it for a few months, please write a blog about your experience. We'll publish it.
I live in the city...
... I own a woodstove, and operate it regularly.
Worcester MA is a veritable urban forest. One of my neighbors makes his living as an urban logger, dealing with all sorts of removal & tree maintenance issues. "Free" wood abounds for those with the means of picking it up, and wood dealers are happy to deliver. At least 3 homes on my block are heated at least partly with wood, and friend across town hasn't run his gas-fired steam boiler in the dozen odd years he has lived there, heating his 2-1/2 story + basement antique exclusively with an airtight wood burning insert.
It takes bit of yard (or a ventilated garage/woodshed) for storage space to heat with wood, and some neighborhoods are too dense for that. But the notion that it's not a viable option for urban dwellers is bunk- it depends on the urb and the nature of the 'hood. But it's clearly not for everyone (rural or urban).
Response to Dana Dorsett
Dana,
Urban residents who want to heat with wood have to consider at least three issues. You have addressed two of them: fuel availability and firewood storage.
The third issue -- the one you didn't address -- is a question of etiquette or ethics: does wood burning in an urban area unfairly burden neighbors who have to breathe the particulates emitted by the wood stove? There is no clear answer to the question, but the question must not be ignored. For more on the issue, see Should Green Homes Burn Wood?
Outdoor Wood Burning Stove
Hi Martin,
Thanks very much for your interesting post. I've been planning the construction of an airtight home and have spent time considering this topic. One solution that had been proposed to me was going the outdoor boiler route (place in a detached garage), with hot water being plumbed into the house. While I agree that typical wood boilers are generally quite nasty, do you have any opinions to offer on the newer, gasification units? For example, the Empyre Elite XT is rated to burn at 0.071g carbon/MJ. Thanks very much,
Response to Yuri Kinakin
Yuri,
For those who insist on installing an outdoor wood-fired boiler, it's important to choose a model that has received the EPA "white tag" certification. It looks like the Empyre Elite has a white tag, so that's good.
I have no experience or knowledge of this boiler, so I can't tell you whether it's sensible to buy one. It costs at least $7,000 plus installation, many times the price of a good wood stove. It requires a lot of electricity to run. I still think it makes sense to spend less on your heating equipment, and more on your thermal envelope. If it costs you $10,000 for your boiler (once it is installed), you might consider instead buying a $2,000 or $3,000 wood stove, and spending the extra $7,000 or $8,000 on more insulation or better windows.
Finally, a fairly high number of purchasers of outdoor wood-fired boilers have complained that many models don't last very long. I have heard reports of rust and leakage. It doesn't take many problems with these boilers before the unit has to be scrapped, and it's time to buy a new one. That's expensive.
Response to Martin Holladay
Hi Martin,
Thanks for the considered response. One quick point is that placing it in a garage should reduce some of the wear and tear on the unit.
The idea of getting a regular wood stove and spending the difference on improved windows is well taken. Our idea with the house is that we're willing to pay a higher up-front cost for a house that will have a low cost to operate. Running an extra water pump for this unit is probably much more expensive that getting a good water heater, a decent wood stove and some high efficiency windows. Thanks for the reality check.
Great article!
You forgot to list one more challenge posed by wood stoves: SNAKES! I have to store my wood in the back yard, and every once in a while, a copperhead snake decides my nice, dry wood is a great place to spend some cold fall evening. That said, it is still worth the risk to me.
People don’t really consider the efficiency and practicality of wood burning stoves anymore. Obviously the E.P.A cares nothing about how much coal is NOT burned when people use wood stoves efficiently. The reality is that they are quite efficient and when really used properly quite enough to heat many areas.
Masonry Chimneys - Supaflu
I have had good experience with 3 Supaflu liners, since the '80's. One, on a 1920's built, 2 story, lined with (broken) clay tile. Ceramic wall tiles in my bathroom were 'pushed' askew, when the liner was installed - indicating how bad the existing chimney was.
The other two, were in a new construction, one was 2-story, the other, 1-story - lining the brick 'hole'. Two years ago, the 'above the roof' part was repaired - new brick, and a liner made with 1/3 Poraver as aggregate in the mix. Supaflu was not used because of the expense, for a small job, in a water access location. I am very pleased. The liner is quite solid (knocking it down) and has a R value (insulation).
I am surprised that I don't see many references to Supaflu. I did not want a metal chimney, that I thought would have to be replaced (by my successors).
Response to John Cross
John,
Thanks for sharing your experiences with Supaflu.
For GBA readers who are unfamiliar with the Supaflu system, it is a cast-in-place chimney lining product used to repair existing masonry chimneys.
Stove air sealing metrics and pressure warning device
Thanks for the comprehensive article. I have read that in an airtight house in addition to combustion air, it's important to have a an air tight stove. I've never seen these statistics published. Is there a good metric for the airtightness of the fire box? Are there brands of stove you can recommend that have better air sealing.
Also,in a very air tight (less than 1 ACH50) house that we built, we installed a small wood stove (with dedicated combustion). The house also has a range hood fan (max 350 cfm at high speed) with a dedicated make up air vent. The owners have periodically smelled smoke (presumably from backdrafting) and we want to find a pressure warning device that could alert the owner when the house is depressurized. Can you recommend one for this purpose?
Question about installing ducting
I have a woodstove installed in the basement of my home with a brick chimney that is located outside of the house. This is doubtlessly not a very efficient set up, and I have been looking for ways to improve the heating ability of this stove. However, both the chimney and the roof of our house is quite new (<5 years), and financially it doesn't make sense for us to install a new chimney up through the first floor. in addition,our space requirments don't really allow relocation of stove that level.
Recently I have attempted to increase the heating efficiency by surrounding the woodstove with a "box" of metal sheeting, then tying some ducting into this box which then leads to the first floor of the house. I have had some pretty good success with this. Without use of any type of fan, abundant heat empties out of the ducting, and it seems to have helped "balance" the temperatures between the two levels. For example all winter, to get the heat to 22oC on the first floor, it would pretty much be 34oC in the basement, while now the ratio is more like 22oC : 25oC
However, I am a little concerned that there may be safety issues or building code violations inherent in to this method. I have tried searching for information on the web, but have so far been unsuccessful. Has anyone heard of this method/any issues with using it? Any info would be much appreciated.
Response to Trent Hardy
Trent,
Indeed, your modifications of your wood stove undoubtedly violate the stove manufacturer's recommendations and may pose a fire safety hazard.
What you are trying to do, evidently, is build a home-made wood furnace. Here's my advice: if you want a wood furnace, buy a wood furnace. (A wood furnace is designed to be hooked up to ductwork.)
Sounds good. Thanks very
Sounds good. Thanks very much for the advice :-)
Burning soft wood
We burn Southern Pine. As long as the wood is properly dried, and a stovepipe thermostat is used to keep the stove operating in a proper heat range, I've found that burning pine creates very little creosote buildup.
A masonry chimney on an exterior wall will always produce much more creosote than an insulated metal chimney, especially an interior insulated metal chimney.
Bill
Links on burning pine
I've attached some links below on the topic of burning pine and other softwoods below.
When you read through the info below, you'll notice that the importance of burning dry wood is stressed a number of times. Also, there are a number of mentions of burning the pine during the day, and using the hardwoods for an overnight burn.
Regards,
Bill
Burning pine wood ? | Hearth.com Forums Home
This question has been beat to death here ,but it keeps popping up. Pine is fine as long as its dry period. Any wood burned wet or green will cause trouble. I burn mostly pine in 3 different brands of EPA non cat stoves,cuz i have so much of it. Only difference is you have to load the stove a little more often.
http://www.hearth.com/talk/threads/burning-pine-wood.115214/
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Southern Yellow Pine easily burns at varying heat levels and is easy to split. It emits some smoke and sparks but makes a relatively good firewood.
Read more:http://davesgarden.com/guides/articles/view/347/#ixzz2o9VMbn80
http://davesgarden.com/guides/articles/view/347/#b
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Back in the early 1980's, tests were conducted to discover which kind of wood created the most creosote in a regular "open" fireplace. The results were surprising. Contrary to popular opinion, the hardwood's, like oak and madrone, created MORE creosote than the softwoods, like fir and pine. The reason for this, is that if the softwoods are dry, they create a hotter, more intense fire. The draft created by the hotter fire moves the air up the chimney faster! Because it is moving faster, the flue gas does not have as much time to condense as creosote inside the chimney. Also, because the flue gas is hotter: it does not cool down to the condensation point as quickly. On the contrary, the dense hardwood's tend to smolder more, so their flue gas temperature is cooler. Thus, more creosote is able to condense on the surface of the flue. So, saying that "fir builds up more creosote than oak" just isn't true! It is a misunderstanding to think that it's the pitch in wood which causes creosote. It's not the pitch that is the problem, it's the water IN the pitch. Once the water in the wood has evaporated, that pitch becomes high octane fuel! When dry, softwoods burn extremely hot!
Which kind of wood is better? That depends on what you want. If you are a first time fire-burner, or if you only want to burn a couple dozen fires a year: definitely go with a DRY softwood, like fir. Your odds for being happy are infinitely higher with fir, especially if you are just now buying wood for this year. The fresh aroma of fir creates a lovely holiday ambiance! Fir seasons quickly, and when it is dry it is truly delightful, trouble free wood! It's easy to get going. It smells great. It's easy to split for kindling. It creates BIG, friendly, luxurious fires! But, it doesn't last as long as oak or madrone! You must feed a stove more frequently to keep it going with fir, and there is no guarantee that there will still be live hot coals in the morning. Cord for cord the hardwood's may be a better deal.
Hardwood's, like madrone, live oak, eucalyptus, walnut, black oak etc., are the choice of the serious fire burner. You may pay $300 for a cord of oak, and only $250 for a cord of fir. BUT, because the oak is more dense, it weighs much more than the fir. So you actually get more for your money with hardwood. In fact, you may get almost twice the fire for the money! Because hardwoods are denser, they provide more available fuel in the same space. So, hardwoods burn longer. If hardwoods are properly seasoned, they do burn very hot. (Look for oak mixed with madrone.) The fuel available in hardwood enables stoves or inserts to sustain high temperatures for significantly longer periods. Also, unless the stove is shut down tight, hardwoods may keep a hot live coal bed for days. So as a rule, airtight stoves, or inserts, perform best with dry hardwoods. It is, however, always important to have a large supply of really good kindling - because hardwood is difficult to start. Having a quantity of fir on hand is great source of good kindling.
When buying firewood, remember that first and foremost, it must be properly seasoned. The best way to get seasoned wood is to buy THIS years wood for NEXT year! For a scrupulous first time wood buyer, a moisture tester may be a good investment. Wood sellers will often tell you that even though this wood was split this year, it will be just fine. Except in the cases of fir or pine, that is not true. Look for gray, or darkened, brittle wood that has a lot of cracks in the inner rings. Seasoned wood looks gray, or dark and dingy because it has been sitting sitting in the sun, drying, and collecting dust for a while. But, if you split it: it's dry and very WHITE inside! Unseasoned wood has the fresh clean look of new lumber at a building supply store. Unseasoned wood has that same fresh look on the INSIDE when it's split. Though seasoned wood is darker on the outside, it's bone white on the inside.
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Southern yellow pine: General rating good, heat produced good.
http://mb-soft.com/juca/print/firewood.html
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Southern yellow pine rated as "good" firewood.
http://thelograck.com/firewood_rating_chart.html
Wood Stove water heaters?
We are planning to heat a well insulated, air tight house with a wood stove - we live in Yellowknife, Canada where the design temperature is minus 45C. Energy modelling shows that we'll need ~32,000 BTU/hr at that temperature.
The article mentions that in Sweden they recommend using a heat exchanger to capture excess heat and Tyler Forbes mentioned in a comment that wood stoves are being made with water jackets.
I have not been able to find a single EPA approved wood stove (not a boiler/furnace) that has a water jacket or any way of heating water. There are lots to find in Austria & Italy, but no-one is selling them here?
Anyone know why? Are EPA emissions regulations too strict for European wood stoves?
Response to Andrew Robinson
Andrew,
Cold water flowing through a coil in a firebox can change combustion characteristics, making it harder for a wood stove manufacturer to show compliance with EPA requirements.
That said, it's possible to drill two holes in some models of stoves -- as far as I know, it's easier to drill holes in steel than cast iron -- and to install a stainless-steel coil in the firebox. This coil is connected (via a thermosyphon loop) to an elevated tank. Before you buy your stove, make sure that the firebox is big enough for this conversion, and that there aren't any firebricks in the way.
Here are two suppliers of stainless-steel coils for this conversion:
Hilkoil
Therma-coil
Wood Stove water heaters? I found one?
Thanks for the links Martin,
As you mentioned, adding a cold water loop to an existing stove would cool down the combustion gases with undesirable results. A large part of the improvements made to wood stoves in recent years focuses on increasing temperatures in the firebox by adding pre-heated secondary air. The results have been great reductions in particulate and creosote as well as increased efficiency.
Cooling the combustion gases with a water loop would likely have the opposite effect - increased particulates, increased creosote and decreased efficiency. These loops would likely also void your warranty and potentially void your home insurance policy as well.
But there are stoves out there that are designed with water heating in mind - sometimes they are called "Architectural Wood Boilers" - meaning they are a boiler that looks nice enough to have in your living room.
In Italy: Lanordica ExtraFlame
USA: Hydro to Heat Convertor - claims to have a model for Pasiv Haus - the Nano. Although the website says "coming in 2011"
I tried to post links to the websites for the above sources, but the spam filter rejected the post :-(
If anyone has experience with one of these, I would love to hear about it.
Any tips on punching a "zero" clearance chimney thorough a high performance roof. Roof has mentos at the top...intello at the bottom. Do we tape these layers to the chimney/roof adapter kit?
Tim,
Depending on the adaptor there may still be a clearance to the combustable construction of the framing which might have to be bridged with flashing. Either the flashing or the air-sealing layer gets taped or caulked to the adaptor.
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