heating/cooling a crawl space
I have a split level with what I would call a “semi-conditioned” crawl under the kitchen/dining/living rooms which are at ground level. The crawl is 30′ x 27′ with a concrete floor about 4′ below grade. There is a 3′ x 3′ opening to the finished basement with a louvered door on the opening. Bare concrete foundation walls. No insulation in the floor joists above. Suburban Chicago.
The main duct runs along one wall and feeds across with round ducts to the rooms above. I consider it semi-conditioned because of the opening to the finished, conditioned basement and leakage from the ducts supplying the main level above. The crawl never varies by more than 10 degrees from the rest of the house, and I’d guess more like 5-6 degrees. The last owner ran a dehum in the spring when the crawl seemed damp.
We are going to be storing all kinds of things in the crawl (we are temporarily downsizing, thus all the stuff stored)/. Storage will be up 4″ from the concrete floor on plywood platforms.
I think it would be fine the way it is, but I’d like to add a little supply air from the hvac to get it closer to the temp in the rest of the house. I have no idea how to size it. Should I just pull a small, 4″ round and put a vent in the center of the crawl and adjust the output until I get a good temp? Or would I be better off with multiple outputs?
Thanks.
Replies
I would put the hvac output register as far away from the existing louvered door as you can. I would go with at least a 6 inch round, and some way to reduce the flow.
If you do not have an air return in the basement, put one in, if you can.
UncleMike42 - I assume you would suggest putting the return in the basement down low to pull the cold off the floor and keep it open just during the heating season, closing it during the cooling season?
I would leave it open year round. in the summer you will want the dehumidification of air from the crawl space, even if it means it is a little cooler than it has to be.
I would put the return somewhat near the floor, but not on the floor, in case of a spill of something that would be heavier than air and not good for your.
The important part is that it pulls air from the space you want to impact. (and not depend on leaky structure.)
Why not use a bath fan that takes conditioned air out of the basement and blows it into the far reaches of the crawl. This will not hinder any balance in the existing ducts. Set the new fan at a CFM that provides an air exchange per hour so you don't highly presurize the crawl. Keep that fan somewhere near the basement access to help draw the air out. If you need to, place a humidity sensor switch inside the crawl that pushes the fan into a higher mode to help dry it out.
ktkcad - that's an interesting approach. I have a spare humidity sensor, so that part would be easy. I'm unclear about what this means: "Keep that fan somewhere near the basement access to help draw the air out." Could you explain?
What about a portable air conditioner for this room?