Crawl space heating/ventilation questions

4 years ago

last modified: 4 years ago

Hi. I have a large crawlspace/ unfinished basement at my house. The crawl space measures approx. 750 sq feet, and is 4.5 feet high. The rest of the basement is standard sized, fit for a living space, and about 1000 sq feet. I had the crawl space recently encapsulated, and the foundation walls in the crawl space are spray foamed. It's it very well prepared now. As I recently had the whole basement gutted, I will be putting up rigid foam on the foundation walls on the basement side myself in the next 2 weeks.

As for heat, I have forced air ducts in basement. 1 heating duct on basement side, and 1 in crawl space. I have one return vent on the basement side, none in crawl space.

After the basement gut, I removed the old electric baseboard heaters which were in the basement side. I will be replacing them after doing the rigid foam install.

I intend to put up a wall between the crawl space and the basement side.

My question is what would be the best way to heat/ventilate this area?

I have read that having a source of forced air into the crawl space is a waste, and having air circulate into the space would be better? ie. adding a fan on the future wall dividing basement from crawl space which will draw warm air into the space.

As it is now, the weather is getting colder and my floors above are getting cold. I need to figure out the best heating/ventilation solution for my situation.

PS - I live in a cold climate. Quebec, Canada.

Here's some images:

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Comments (3)

worthy
4 years ago
last modified: 4 years ago
Whether you're adding a duct or using a fan, you're heating the crawl.

In any case, Building Science Corp. says treat the crawlspace as part of the conditioned living area.

To reduce thermal bridging, use handheld foam spray between the wood framing and the foundation wall and low-expansion foam behind or around the electrical panel and window framing if possible. Also, run horizontal glue beads behind the foam boards to short-circuit air convection loops between the insulation and the foundation.
Seabornman
4 years ago
I'd just cut a new adjustable grille or two into your existing ductwork in crawl space. Then you can determine how much heat is enough to keep the floor warm, and to keep humidity under control. It looks like a good encapsulation job, so humidity shouldn't be much of an issue. Of course in transition seasons you won't be getting airflow.
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Charles Ross Homes
4 years ago
It's hard to tell from your photo, but it appears that the rim joist (band) of the floor system isn't insulated. That's where the majority of air leakage occurs. If it's not insulated, then your encapsulation contractor didn't do their job right and you'll have colder floors than you should.

It also appears that the main trunk lines of your duct system aren't insulated. I suspect the joints are not sealed either. If the crawl is properly insulated, I think you'll find the air leakage from the ducts to be adequate for conditioning the crawl space. That said, sealing ductwork and providing a controlled flowrate of conditioned air to the crawl is preferable. I use an axial fan (the same type used for radon mitigation) to supply air from the living area to the sealed, conditioned crawl space foundations on which we build the majority of our homes.