Fresh Air Supply in a Tight House
Dear GBA friends,
-I’m hoping to make my home pretty air tight, as I have high ceilings throughout.
-Air tightness complicates other things too, though. A brief overview of my situation.
-Western Oregon, climate zone 4, mild & rainy winters, hot dry summers.
-Woodstove (Morso 7110) has the option to duct air into the back, which I didn’t do yet. Stove is installed.
-Midea Heat Pump (ducted) will be installed with short duct runs to two wings of the house from a central closet. The current plan is to have the air supply via a louvered closet door.
-Shower fan is 100 cfm, set to run via humidistat, with a manual switch override.
-Powder room fan is 80 cfm, runs on a timer.
-Stove vent hood is 250 cfm max.
-I do not have plans to install a dryer.
-Crawlspace is conditioned, and the plan is to circulate air from crawl into house via a fan, through a filter. Something like this (https://www.acinfinity.com/hvac-home-ventilation/crawl-space-basement-fans/airtitan-t3-crawl-space-and-basement-ventilation-fan-6-temperature-and-humidity-controller-ip-44-rated/)
-Air return to crawlspace can be through a grate, with filter again if necessary.
-If anyone recalls my previous post, I have now installed plastic on the crawlspace floor, which I hope will reduce further moisture/mildew in the crawlspace. I have also mixed up a bucket of white wash with which to coat the underside of the subfloor, and floor joists, as some mildew had formed prior to my putting plastic down. All this to say that I hope I will have a somewhat pleasant crawlspace, and I will monitor the humidity down there. I know the idea of sharing air between home & crawlspace is controversial.
But the main point of this post is to try to learn more about air balancing.
I hope to finish air sealing around my windows and doors with backer rod & caulk. Other penetrations have been detailed carefully. Then I can get a blower door test done to determine how tight my build is. I do not have insulation or drywall up so presumably I can fix things if the envelope isn’t very tight yet.
1) I could install an outdoor air supply kit to my stove. Should I wait to see how the wood stove performs first, before doing this? I understand that installing this kit would prevent the danger of backdrafting.
2) I am curious how the air supply kit wouldn’t be a big air leak. Is there a way to open/close it, as one does with the damper in the front of the stove? Does it close when there is no fire?
3) When I think about the big picture of my home envelope, I have 3 places where there will be intermittent exhausting. Aside from the possible addition of an air supply to the wood stove, I do not have any other fresh air being added into the home (yet).
4) I had considered a Heat Recovery Ventilator (HRV) but backed away from that, as it seemed excessively complicated and expensive. Also, I have been told that these make more sense in places like Vermont where winters are very cold.
5) Is there a way to supply air into the home on an as needed basis? Like if I were to be running a bath fan AND the stove vent hood simultaneously, then some mechanism would open and allow fresh air in through (perhaps a mini HRV)?
6) I do not intend to ALWAYS keep my windows closed. My home is located in the country, and from time to time I do hope to experience bird song, or the sound of rain. It has been pointed out to me that life in a perfectly sealed envelope isn’t the greatest. But when it’s damp & clammy out, I am sure I’m better off stepping outside rather than opening a window and letting the warm air rush up to the ceilings.
I would like to take it slow and add complexity on an as-needed basis, but at the same time, now is when my walls are open, so if there are systems that must be added, this might be a good time.
I look forward to hearing more. Please let me know if you need more details in order to respond, and thanks in advance!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part