Air Exchange for Unvented Insulated Crawlspace
My crawlspace is unvented and insulated. As I am about to install the heating system, it is time to look at how I will circulate air within the house into the crawlspace.
-I do not yet have the 6 mil plastic down on the ground. I had hoped to do that after the bulk of the underfloor work was complete in order to minimize the damage to the plastic from crawling on it. There is round river rock on the crawlspace floor right now. Maybe I should have put the plastic under the rock but it’s too late now.
-I have no holes cut in the floor of the house yet.
-My HVAC professional is installing the heat pump system. It will supply air to both wings of the house from a closet, via ducts that are not very long, but it’s not a ductless system, in case that matters.
-I’m hoping to DIY the fans & return grills to exchange air with the crawlspace. The site I’m exploring is ACInfinity. Their tech support seems helpful in terms of thinking through options.
-I’ll use a fan like the T3 here, which is humidity and temperature controlled, to push air into the crawlspace. I’m thinking the sensor should be located in the crawl.
-I could just use a passive return grille like this
-My crawlspace is a bit musty right now as it’s been unvented for about a year now. Getting the ventilation set up, running fans, putting plastic down, and (if necessary) painting a limewash on the underside of the floor if needed, could all address any funkiness that has developed.
-I have a good drainage set up (rocks, pipe) outside the foundation, did all the recommended waterproofing, dampproofing etc so hopefully that will take care of me until I have gutters, downspounds on the building which of course feels pressing but may not happen for 6 months.
I’m on the rainy side of Oregon. (Hence the worry about funkiness developing in the unvented crawlspace.)
I have no familiarity with what is standard practice with exchanging air into & out of the crawlspace. I’m posting here to find out if what I’m proposing sounds fairly normal and acceptable. What is the standard practice?
-The underfloor ventilation requirements are 1 CFM per 50 sq feet”, which would mean 18 or so cfm would take care of my 868 sq. ft. house, according to a local building official.
-The T3 fan linked above is 120 cfm (and 30dba) so just having one fan seems adequate for the entire home.
-Would it be advisable to filter the returning air somehow? Or is that not necessary since I’ll have the plastic down and space should be dry.
-If I do install filters, the ACInfinity person suggested that having fans for the return would assist in making that filtration more effective.
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