Fresh air inlet locations in exhaust only ventilation system?
After a couple years going back and forth on how to ventilate my new home (under construction), I have decided on the simple exhaust only ventilation system, using the bathroom exhaust along with a fresh air inlet. I have chosen this route over an HRV for a number of reasons.
Question I have is where to put the fresh air inlet so A) this system will work its best and B) so the inlet doesn’t create uncomfortable drafts? (I assume up high)
Other questions:
-Would two inlets located in different locations be better than one?
-I see many inlets on the market. Are some better than others?
-Should inlet/s be avoided on the windward and leeward sides?
-How often should the programmable timer kick the bathroom fan on and for how long at a time?
For context, my home is under 1000 sq feet, bedroom on the west side, kitchen on the east, living and bath in the center. I’m building it as tight as I reasonably can…though a vintage side door and the entry door I’m making will likely be weak points. It will just be my wife and me 90% of the time. My roof structure is plank (t&g) & beam (exposed, no attic)….single pitch shed, 2:12 slope. R50 roof, R30 walls, R20 under the slab. The ceiling goes from 8′ tall to 12′. The house will be passively solar heated with a wood stove for supplemental heat. I will also have a range hood and dryer, of course. I’m in zone 5, dry.
EDIT: I should also note that I will take full advantage of passive venting during the summer, with casement windows acting as scoops on the windward side and opening the opposite direction on the leeward side. I also have an operable window at the highest point which will be left open throughout the warmer months. I will have no AC. I will only be using homemade natural plasters and paint inside, will use no manufactured/engineered wood, etc…thus I have little concern with IAQ as far as finishes and building materials are concerned. My primary concern is adequate ventilation in the colder months.
Thanks,
Dean
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Anyone?
You're building a fairly well insulated home for 5A, and heating with wood/passive solar. Just curious on the exhaust only strategy where for similar power use, you could use an ERV and not give up those winter BTUs.
Otherwise, I'd be bringing in cold air in the warmest spot in your home, but you should think about prevailing winds etc. so that the risk of pulling smoke back in (even the efficient stoves will smoke during warm up) is mitigated. You'll also want to make sure cool air is not blowing directly on you and your wife. Around 40-50 CFM equivalent would likely do fine for two occupants. A lot of IAQ issues will come from cooking, and for sure, back puffing when loading your wood stove. Humans are also sources of VOCs.
Are you planning on filtering incoming air?
Dean,
There are pluses and minuses to your plan. You may want to read this article:
"Passive Air Inlets Usually Don’t Work."
Thank you, Dennis and Martin.
A standard HRV is not an option for me since I have no space for duct work. My ceiling is plank and beam, and my floor is slab on grade (serving as part of the mass for the the passive solar system).
The building department told me I could do a blower door test and, if the house was leaky enough, I wouldn't have to provide anything but the bathroom fan which I will have anyway. Otherwise, I would have to provide a hole/holes in the wall.
The other option the building department will allow is a simple single room HRV or ERV ventilator such as the following: https://www.arcticasolar.com/products/iv50-gen-1-0 . These things suck air out of the building for ~1 minute then reverse and bring in fresh air for ~1 minute...continuously, or for a set time.
Initially, being the above single room HRV or ERV is less money than a blower door test, I thought this was my ticket. However, I reasoned that they would be no more effective (and perhaps less so) than choosing a simple hole in the wall and utilizing the bathroom fan. Holes would be simpler, and I wouldn't have to worry about the maintenance and replacement costs of the HRV. I also have to consider my budget. I am already well beyond what I was intending to spend on this house....by a large sum.
With those circumstances in mind, particularly my budget and considering the cost of a blower door test ....it seemed the simple hole/s in the wall made the most sense to me. For what ever reason/s, the building department is pretty convinced my house will not be leaky enough to rely on the bathroom fan only. And, if the blower door test proved them wrong, and the house was leaky enough, I'd still be out the cost of the blower door test.
To reiterate, I would only have to get through the winter months as we prefer to have our windows open during the rest of the year.
All that said, I am not rigid on what I believe is the best option for my case. I would need a good convincing otherwise.
Dean,
Bringing in unconditioned air does make the location more challenging, but I'd still concentrate on making sure the path from inlet to exhaust brought the fresh air into the areas that need it most. First among them are bedrooms which can see high levels of CO2. Then kitchens, which need make-up air for the range hood. As the living areas are usually open to he kitchen, they can often piggyback on that.
The complications are what Martin pointed out: The path can reverse. The inlets are as likely to draw air out as in, so that needs to be taken into account. I have a passive vent in my living room. If the range hood or dryer is on, the make-up air is as likely to come down the chimney as through the vent.
Thank you, Malcolm.
Regarding the path reversing.... would a backdraft damper not work?
Also, do you have any thoughts on the small HRVs like the ERV I linked to....as in how they might compare to my idea of using passive air inlets and the bathroom exhaust? My feeling is that a couple of fresh air inlets (one in the bedroom on the W side of house, & one on the E kitchen side w/ bathroom fan in the center) would work better for moving air.
Dean
Dean,
I'm not sure that the air-pressure on the inlet vents is high enough to open a damper. But then I'm not sure that the vents working as exhausts occasionally is that big a problem in such a small building. Our code has allowed houses under 1800 sq ft to use an exhaust only system, and they work fairly well. Partly that's because the climate here in south coastal BC is pretty temperate. The big disadvantage in colder ones is of course the lack of heat transfer you get with HRV/ERVs, and the energy penalty that comes with that.
I don't have any experience with small spot ERVs. What little I've read hasn't been particularly encouraging. If you decide to include an ERV, I'd try and find a closet or other small room you could drop the ceiling in, and use one of the regular units with minimal ducting.
Malcolm,
Thanks for the addition thoughts and info. Since posting, I did learn of motorized dampers. Perhaps they could be put to use in my situation?
I also ran across one of Martin's posts mentioning a designer from British Columbia ducting exterior air to a grille behind the refrigerator, so the incoming cold air improves its efficiency while the refrigerator coils preheat the air. Referred to as the "poor man's HRV". Not sure how effective it would be but, it seems a clever idea. Thoughts?
Dean
Dean,
The problem with these sort of ideas is we really don't know how effective they are, as no one quantifies them. I suspect the savings are marginal at best. There is a similar problem with passive vents, or opening windows. The rate of exchange varies wildly, and is hard to predict. That's one of the real advantages of mechanical ventilation.
Thanks, Malcolm.
A fair and honest response from you.
Dean
It’s very difficult to retrofit an ERV. Your IAQ will be compromised with the woodstove. You seem to be trying to do all the right things except for not building as airtight as possible and using ventilation to Improve the air quality of your home which will improve comfort and health.
Rondeaunotrondo,
It appears you did not read my posts, or perhaps you only gave them a cursory look.
I haven't space for the duct work of a conventional ERV/HRV. And I am trying to build as airtight as reasonable. And I am trying to figure out a way of ventilating....that works for my particular situation. That's why I am here.
What is your suggestion?
Regarding the retrofitting of an ERV: The type I linked to would not be difficult at all....particularly if I pre-wired. But, in the big picture, I'm not sure one of those little units would work any better for me than passive air inlets.
Not sure if you’re trying to insult me with this comment. Generally folks on here are trying to help you with their opinions. It seems like your mind is made up already about what to do. What I was trying to say is, I would do everything in my power to find a place for an ERV, which can bring in fresh air in a controlled, titrated manner, which is filtered as opposed to drilling holes in the wall that decreases air tightness and at times when there’s no pressure , Temperature or humidity difference Will do nothing. There needs to be a gradient for air to move. You’ll certainly will be burning a lot of wood since that is your only heat source and your outside air will have very poor IAQ. I know this because I’m surrounded by houses that Heat with woodstoves as their sole source of heat. The smoke will be pouring into your house through passive inlets or open windows. Without some sort of filtration, what is your plan for this? I’m not trying to contradict what you’re doing, but, For myself, I would be doing everything possible to make my home as healthy and comfortable as possible.
No, I wasn't trying to insult you. It did seem to me however that your response was a little disparaging, particularly after I stated up front that I was trying to build as tight as reasonably possible. I'm trying to do the best job I can with what I have to work with. Thinking about your response now, I think it was just how you worded things and how I read them at that given time. I don't believe you had ill intent, and I know I didn't.
My mind wasn't/isn't made up, and I made it clear that I was open to other ideas...if they fit within the parameters I have to work with: my style of construction and my budget. As I said before, I am already well beyond what I was intending to spend on this house....by a large sum. To my wifes dismay, and mine, I am bleeding our savings away. I need to choose wisely. The mistake I made was not saying what I thought our budget could handle. We're ok spending $400-$550ish. Yet, I'm not convinced the options we get for that amount would be much better in our case than an exhaust only system which could be done for ~$50ish. In summary, I was hoping for some ideas that would help us get the most out of what is seen as less than ideal in some peoples eyes. I should have put a $ limit on it though.
That said, since my last post, I did run across the Fantech SH704, and figured out where I could put it and how the ducting could be concealed, assuming I combined the inlet and exhaust into one of the tandem transition kits. However, my oft time voice of reason (wife) still favors giving the exhaust only system a try first. Try and if it doesn't work for us, install a less pricey Lunos style or, better yet (I think), the SH704. Rather than try to explain, I will just say that retrofitting these sort of small HRVs is not a problem in our case....if a tandem duct kit is used.
Thanks for your followup post and explanation. Appreciate it. Also thanks to all the others here, particularly Dennis who was good to humor me. :-)
And, as always, I am always open to more feedback, ideas, etc.
I have a retrofitted small Fantech HRV ( i will have to lookup the model number) in a slab on grade house. I ran the insulated intake duct across the attic, dropped it into the living space in a small soffit - and out the side of the wall below the eve/soffit . For the exhaust I ran it though the attic and terminated at the gable end wall. for the inside ducting i just ran inside the living space on both sides of a closet, intake is in the living area and ten feet away the the exhaust is in a hallway near the bedrooms.
I have used passive makeup air ports and Lunos through-wall HRVs. The Lunos HRVs worked better.
This is a good overview article on ventilation requirements: https://www.greenbuildingadvisor.com/article/designing-a-good-ventilation-system
Thank you, Michael.
I believe the Lunos was the unit that turned me onto these through-wall HRVs. Their cost is pretty prohibitive for me at this point.
Thanks for the link. I had read that article before...and so many others that I feel to be developing analysis paralysis.
Dean
They are pricey for sure. If it helps, I would estimate that bringing in unconditioned air in your climate zone will cost you at least $100 a year in energy costs. While that's pretty affordable, in ±15 years you would pay for a Lunos unit.
You can also look at this Panasonic spot ERV running continuously for 30 CFM supply, and 40 CFM exhaust. It can be wall mounted as well between studs:
https://na.panasonic.com/us/home-and-building-solutions/ventilation-indoor-air-quality/energy-recovery-ventilators/whispercomfortrerv-balanced-air-solution
Passive inlets need to be a lot larger (by a factor of 3 or 4) vs the fan exhaust's duct size to work effectively, otherwise you'll pull negative pressure and find your woodstove is back drafting a lot.
I ran one of the small Panasonic units for a few years. For your climate zone, and two occupants in a smaller space, it would work fine. For colder climates, it's not all that efficient. Malcolm's suggestion of installing a larger ERV in a closet (with minimal ducting) is not a bad idea if you want to dial in ventilation rates a bit higher, and ideally go a tad positive pressure to keep your stove happy. That way you could get your efficiency up to 80-85% at a 50-60 CFM vent rate without breaking the bank. I have ducting challenges as well and am now using a standalone (minimal ducting) setup installed in a tall basement stairwell ceiling that I was able to drop 24", creating an installation space for the unit and ducting.
Thanks, Dennis.
I took a serious look at that very unit early on. It has an automatic frost prevention mode though which, disables the energy recovery function. At that point, it works as a normal ventilation fan. According to their recommended zones map, it would not be useful for me when I would want the energy recovery function the most: During the winter months. Perhaps that is what you were referring to when you said it's not all that efficient in colder climates?
As far as mounting a larger ERV in a closet....I like that idea. However, it would come as a big sacrifice for space, as we're already tight as it is. And I would almost certainly have ducting exposed on my otherwise clean plank (t&G) & beam ceiling. So, aesthetically and spaciously....it isn't an attractive option for us.
Dean
I've used that spot ERV in zone5 without issues. The amount of time outside temperature falls bellow its exhaust only limit is small so you still get some energy recovery the rest of the time.
Overall, it is still a way better efficiency than any exhaust only setup. The only drawback is the low flow rate, so it is only really good for about 2 bedrooms.
That Panasonic is exhaust only (at a lower rate) when you get into the -25C range, however it just uses a defrost strategy on a timer basically as temps drop below freezing. What's your lowest likely winter temp? You don't necessarily need ducting at all if you can separate the supply and return inside by 10-15 feet and have them in different directions inside, into your common space. That could be in 8" soffit for example on an inside wall, say on both sides of utility or storage space exiting into your living space.
Lunos is a great idea, but it falls short on three points (at least in my opinion). They are essentially open tubes to the outside with very little potential for any kind of noise mitigation, effective filtering, or vapour transfer. If none of those points are considerations, then use them.
Thanks, Dennis.
After looking through these messages again, I see that I failed to answer your question of filtering. We have always lived with our windows open...so whatever we install, filtering is not a priority.
To answer your question about lowest likely winter temp: It rarely gets below 0 F here...and our average low during the coldest month is 24 F.
In considering the Panasonic...I walked around yesterday and found a spot where it would fit: Above our couch...somewhat centrally located. We had reserved that space for a painting but...as ugly as the Panasonic would be in comparison, at least I know it could go there.
My line of thinking is as follows. Please correct me (you or anyone else) if this thinking is wrong or skewed. Seems to me the Panasonic would be better than something like the through-wall Lunos style. In terms of pure ventilation though, both styles have incoming air and outgoing right next to each other. I could see the air quality being better in the near vicinity of the unit but I don't see it reducing the CO2 levels in the bedroom for instance. In that case, a Lunos style becomes more attractive to me as there are several locations in which I could place one...all of which would be far less obtrusive than the Panasonic. And, speaking of the Panasonic.....with the incoming and outgoing air so close to each other, what prevents the air from just going in a circle, like a dog chasing its tail?
This brings me back to my original idea of using passive in-lets combined with my bathroom exhaust. Assuming my house was tight (which as I understand is the key to making an exhaust only system work)...I could provide an inlet in my bedroom which is on the NW corner of the house, and another near the kitchen on the SE corner of the house. Being that my bathroom is more or less in between these two corners.....it would seem to me I could get some actual cross ventilation going which, in my mind, would provide a more thorough job of providing different areas of the house with fresh air. With the Panasonic (or Lunos) out in the living room....I don't see how it could lower the CO2 levels in our bedroom better than having a fresh air inlet in the bedroom. Sure, there could be some drafts....in the bedroom and kitchen...but I'm not sure I would care since I'd be in bed under the covers. And during the day, we'll have sun streaming in through all the south facing glass in the living area....and will not be in the bedroom. I don't feel the potential drafts would be noticed that much, day or night, particularly if the in-lets were up high. And it seems the potential for better air mixing would be better than having a single Panasonic in the living.
Of course, all this is coming from a guy who grew up in a home in this area built in the early 1900s that had little to no insulation...a guy whose current home is leaky as a sieve, has r13 walls, r19 roof, and a slab on grade with no insulation. I also drive a truck old enough to have wing vents which I favor over its AC. Oh, and did I mention that I didn't have a cell phone until I started constructing this house in 2021?
Though I am not a complete luddite, and I am still open to the Panasonic (or Lunos style)...I do place high value on the KISS concept (keep it super simple) in most everything. As such, I am still favoring the exhaust only method. Not only simple, it saves me $. I could try it and if it didn't work well, I could retrofit in the Panasonic (or Lunos).
Thanks to all who have the patience to read through this and offer their insight.
Now.....Dennis, or anyone else have additional thoughts on this?
"In considering the Panasonic...I walked around yesterday and found a spot where it would fit: Above our couch...somewhat centrally located. We had reserved that space for a painting but...as ugly as the Panasonic would be in comparison, at least I know it could go there"
This is not the best idea. Even with a higher efficiency units, the fresh air supplied in the winter is colder than the room temp, last thing you want above a couch.
Generally all the Panasonic stuff is very well engineered, I would assume mixing was an item they looked at in detail. Their tandem hood also has the intake and exhaust pretty close but still works.
I have my ERV in a cabinet at the end of the kitchen. The fresh air is brought up through the cabinet and and blows towards the peak of the ceiling. Stale air pickups are ducted to rooms, so that would be hard to do without floor joist space. One option to hide the ducting is to box it with wood to match the existing beams, might work.
Akos,
Thanks for the info. I wouldn't have thought about the couch location. I have since figured out another spot to place a small HRV and how to conceal the minimal ducting. If we do go that route though, I'm leaning towards the Fantech SH704. Seems a better fit for our situation and it would still be within our lean budget. However, my wife prefers to try the simpler and less costly exhaust only method first. If that doesn't work for us, we can then retrofit the HRV without issues.
Dean
one thing to remember is it probably needs to hit a drain for the the condensate water.
I'd say go exhaust only if you had not expressed an interest in efficiency :-) At 24F, the supply air coming in from outside will be cold in an exhaust only strategy. To add, with an exhaust only system running at 40CFM, and 24F average outside, you're looking at 1987 BTU to heat that air to 70F. For a small, efficient space, are you OK with that energy hit? I have an air tight high efficiency fireplace and any bit of negative pressure results in back smoke when loading. The automation system runs our HRV asymetrically when using the fireplace, to increase supply about 30 CFM over return. This resolves the back puffing when opening the door to load the unit. If you run an exhaust only system, unless your fresh air duct is either 4x larger than exhaust, or fan driven, your space will be depressurized and back smoking will be an issue.
KISS is just opening a window a bit. I would not bother with an exhaust setup at all as I don't see what advantage it provides over just cracking a window open in winter.
I'd still make the effort to incorporate some ducting (like soffit at the top of a northerly oriented exterior wall) and take a look at a compact standalone ERV. The Intellibalance units are pretty compact and the FV-10VEC2 is set up for cold weather as well: https://na.panasonic.com/ca/indoor-air-quality/fresh-ventilation-filtration/energy-recovery-ventilators-erv/intelli-balancer-100-50-100-cfm It should run under $1K USD and has decent efficiency at lower ventilation rates.
You can also unbalance that unit to slightly pressurize your space to deal with your wood stove.
Dennis,
Thanks for your help, and humoring me. :)
I should have been more clear about our budget. You can see my response to rondeaunotrondo. For that reason, my wife (my voice of reason) prefers to try the simpler and less costly exhaust only method first. If that doesn't work for us, I can retrofit a small HRV without issues.
Dean
Dean- Here's what I did in my tight home(Remote wall with 4" rigid insulation). I DID install an HRV and duct work, but needed fresh air due to the draw of 2 bath fans, woodstove , and future range hood. My woodstove had an option for a 4" proximity fresh air duct which I installed years ago and worked ok as long as I didn't run a bath fan and try to start a fire. With the planned install of the range hood I knew I would need more air so I enlarged my fresh air inlet to 6". Yes, my woodstove is close to an outside wall. Is this a perfect fix? No. I can fill the house with smoke if I run the dryer and have a bath fan running with a less than a hot fire. But...the air that I am bringing in (I'm in Anchorage, so it can be cold) is running into the back of my hot woodstove so I do not notice the extra cold air as it's coming into the warmest area of my home. I did add a manual damper to my set up so I can adjust it/close it due to uses. I know this won't bring fresh air to your bedrooms, but I think you would regret those holes if you felt that cold air coming in.
Thanks for sharing your experience. I have few regrets with my house thus far. The one and biggest is that I didn't provide a way I could run a fresh air duct directly to my wood stove. It's difficult to explain its location other than to say the stove will be located in the center of the home, like an island, no where near an exterior wall. I had so much going on during the concrete prep that I totally forgot about it. Otherwise, I would have placed a duct under the slab.
My set up:
That's awesome user_8675309! ( i am in anc also!)