sealing around ducts, through foundation wall?

consider insulating the crawl space, begin with plastic tarps oncrawl space floor. you can use foam board for insulation

Hi, If it is always dry. If moisture is present at times, like rainy summer, sealing floor is bad idea? My cabin has crawl space. Gas furnace and electric WH are located there. Skirting walls are insulated with R20 fiberglass rolls and vapor barrier. Ceiling(floor of living space above is done same way) Crawl space is very warm even in dead winter. Maybe use spray foam?

Great Stuff expanding foam comes to mind. At hardware store, and also Walmart in the paint section.

Some advice is needed, before using the stuff.....

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That's what I was thinking too for the stated purpose. But there are other possible issues, eg are the ducts insulated in the cold crawl space, floor insulated, etc. If not, the holes the ducts pass through may not be the biggest issue, having some fiberglass in them already.

Are there any water lines in the crawl space area? If so, keeping some opening between the crawl space and the basement may allow enough warm air from the basement to enter the crawl space to keep the water pipes from freezing.

Foam. Via spray cans of same.

On further thought, I think I'll block it in as much as I can, and then back the corners gaps with wire lath, and use that as a base for layering the foam. It's just a lot of effort. I don't know what I was expecting - magic, I guess. Oh well.

Thanks for all the replies.

If it's large, you don't have to fill the large parts all at once. You can do it in a couple stages. But unless it's really huge, I don't think you have much to worry about. If it's cement block, there will be enough air movement that it will cure. Seems to me it would also be easy to fill any of the larger parts with some insulation, anything that you can stuff in there easy. Wire lath wouldn't be my first choice.