Is the exhaust fan in the crawlspace there for conditioning the crawl or for radon mitigation, or both? Conditioning requires air movement through the crawl. If there is not an air supply and return to the house, the fan may be doing the job of conditioning by pulling house air into the crawl via leakage or just from one supply to the crawlspace.

Hello and thanks for your reply. There is a supply duct in the crawlspace providing heated air and cooling. The duct supply extends to various parts of the crawlspace.

Patrick

Where do you live?

Hello

I live in BC on vancouver island.

Thanks

Supply only in crawlspace. No return however I will need to look again to confirm this....

Seems from this video I would only need one and not both. So either ducted air into the crawlspace or exhaust.

https://www.youtube.com/watch?v=GJanmGxS9cY

Its basic physics that a supply can't supply without a return and vice versa. Some rely on leakage for one or the other, but that's just bad science. The video talks about supply AND return. For example, if you provide a supply duce, the return can be gaps below doors back to the house or a transfer grille setup; that gives you both a supply and return.

Hello and thanks again. I just checked and there is both a supply duct and return duct.

Usually, you don't have radon issues in a sealed, conditioned crawlspace. The fan is to mitigate radon but, as you say, defeats the point of conditioning!

Hi, Wormdoggy,

Until recently, sealed, conditioned crawl spaces weren't included in the prescriptive building code. It might appear like an oxymoron, but a "sealed, conditioned" crawl space has a ventilation requirement in the International Residential Code (IRC) which forms the core of most state-wide building codes. You'll find it in section 408.3 of the IRC.

"Ventilation" requires both supplying air to and exhausting air from a space. There are two prescribed methods to meet the IRC ventilation requirement. One of the prescriptive methods involves supplying and returning conditioned air to/from the space. It's a requirement that fails to consider the effect of circulating soil gases such as radon, or insect fragments or rodent droppings that might be in a crawl space through the home's HVAC system.

I think the better approach is to supply air to the crawl space and exhaust it at a controlled rate using a fan and a transfer grill in the floor of the living space. This will have the effect of conditioning the crawl space and reducing the concentration of soil gases such as radon. I think this is what you have installed in your home. Don't remove the fan.

Thanks Charles I appreciate all the responses.

Patrick