Ultra-inexpensive balanced ventilation
I am building a very tight, single story, 960-square-foot house with an open floor plan in central Arizona, where winter temperatures go from 25 at night to a peak of 50 and summers go from 70 at night to a peak of 100. The house will be heated and cooled by a ductless mini-split. I will install a ceiling fan in the bathroom that continually exhausts 50 CFM. I will also have a range hood that moves 190 CFM, but I will rarely use it, as my house will be all electric and the only cooking I do is light boiling and gentle baking. I understand from the articles and discussions at GBA and elsewhere that my $40 bathroom fan could be my sole mechanical ventilation and, as an exhaust-type system, it would suck air through small leaks in my building enclosure, but encouraging air to come through the walls, ceiling, and especially the floor above my unconditioned crawlspace seems less desirable than exercising more control over its entry. A supply-type system would give me more control over the incoming air, but pushing air out through my walls, etc. also seems less than optimal. A balanced ventilation system using an HRV or ERV would offer many benefits, but the cost wouldn’t make sense in my climate.
Here’s my idea for an ultra-inexpensive balanced ventilation system, albeit without the heat recovery or energy recovery: I would balance my bathroom exhaust fan with a supply fan that pushes an equal amount of air into the house. The pressurizing effect of the supply fan would counteract the depressurizing effect of the exhaust fan so that there would be less pressure driving air through my walls, ceiling, and floor. I understand that wind and the stack effect would still create their own pressure gradients, but the same would be true with an expensive HRV or ERV. I have a good spot for the supply fan that would result in fresh air flowing through the parts of the house I most often occupy on its way out through the bathroom without creating uncomfortable drafts. A 50 CFM supply fan shouldn’t cost any more than my $40 exhaust fan, especially if I can just turn an exhaust fan around or reverse its rotation. If both fans are 50 CFM, the supply fan will probably pressurize a bit more than the exhaust fan depressurizes, because it will be mounted right on an exterior wall and therefore perform better, not having to push air through a duct as the exhaust fan will.
Does this idea make sense?
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Replies
I'm in a very different climate (NH), but could probably give some helpful advice based on my recent experience (tight house, exhaust ventilation).
If your cooking is that light, I would suggest a recirculating range hood so you don't have to worry about make up air. Or no range hood at all (this is what we did and it has worked out well). With light cooking and electric, you really only have to worry about moisture and that can be taken care of with windows/ventilation/AC.
If you go with a bathroom exhaust fan for ventilation, I'd suggest a Panasonic WhisperGreen and specifically this model:
http://www.amazon.com/dp/B004UHWP2K/ref=pe_385040_30332190_TE_M3T1_ST1_dp_1
This one can run as low as 30 CFM continuous, which may be enough, and it can be turned up in 10 CFM increments if you need more. It can then be switched on to full 80 CFM, either until you turn down or with a timer so it runs 80 CFM for anywhere from 30 seconds to 60 minutes.
I don't have experience with supply fans. Your other option for makeup air would be passive air inlets. There are some other models, but we used the Panasonic FV-GKF32S1, looks like they are around $50 at a couple places. They are supposedly capable of 12-18 CFM depending on setting, but we found (and read another review) they only allow around 10 CFM or so. Some options:
http://www.iaqsource.com/category.php/passive-inlets/?category=2869
So, if you think 30 CFM continuous would be fine, you might want to install up to 3 of these, spread between bedrooms and living areas depending on your room count. Then crack a window when you need the 80 CFM.
You could consider a very basic ERV or the Lunos system, but the bathroom fan approach seems like a reasonable choice in your situation.
I'm not a builder, building scientist, or sure if this makes the most sense...but my $0.02.
Panasonic makes spot ERVs that sell for under $500.
http://www.amazon.com/gp/product/B007DRSKNC?keywords=panasonic%20hrv&qid=1445815912&ref_=sr_1_sc_7&sr=8-7-spell
Thank you, Brian and Malcolm, for your recommendations. I considered a recirculating or no range hood, but the one I found at Home Depot is only $40, I'll use the light if nothing else, and it will be there if I ever sell the place to someone who cooks more pollutingly than I do. The Panasonic ERV is available for $350 here: http://www.amazon.com/Panasonic-FV-04VE1-WhisperComfortTM-Ventilation-Patent-Pending/dp/B000XJNZ1Y/ref=cm_cr_pr_product_top?ie=UTF8. It isn't conducive to creating a flow of fresh air through the house and out the bathroom exhaust, and of course it wouldn't balance out the bathroom exhaust's depressurization, but it could be a nice addition to a room.
Jeff,
You've gotten good advice from other readers.
Your suggested balanced ventilation system would work, but it comes with an energy penalty compared to an HRV, ERV, or even the exhaust-only option. (Since the exhaust-only option pulls some of its makeup air through walls and other insulated assemblies, the makeup air recovers heat trapped between the insulation fibers -- so this makeup air is warmer and more energy-efficient than makeup air furnished by a supply fan.)
My advice is to live with the exhaust-only option for a year to see if you like it. You can always add a supply fan later if you want to. Brian is also right when he suggests that you may be satisfied with less than 50 cfm of ventilation.
Thank you, Martin. The variable-speed bathroom fan Brian suggests would be great for experimenting with how much ventilation I want and for adjusting for peak demands like taking a shower.