Insulating crawl space ceiling


Old 02-14-18, 01:38 PM
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Insulating crawl space ceiling

I have a crawl space in my house located directly under the family room. The only thing in the crawl space is the boiler, so it can get quite warm in there, especially in the winter. For some reason, the crawl space ceiling is insulated with regular fiberglass insulation, which in my view only keeps the warm air trapped in the crawl space stopping it from coming up into the family room. So, I can't really understand why the insulation is there.

I'm thinking of removing the insulation, but wondering if it's there for a reason. But is there any good reason to insulate the crawl space ceiling? Thanks.
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Old 02-14-18, 01:54 PM
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My guess would be for noise reduction from the boiler.
Old 02-14-18, 01:57 PM
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Hi David,
A typical approach for a crawlspace in a cold climate is to encapsulate it. If it has a dirt floor that would need to be covered with a plastic (or other) vapor barrier and sealed. Then walls and rim insulated and also air sealed. Once encapsulated that air space is suitable to be shared with the rest of the house adding that heat back into your budget.

Is the floor in there dirt or concrete?
No vents I hope.

Being a boiler there are pipes that will benefit from the encapsulating.

You say it gets very warm and that heat should be utilized. As for the insulation in the ceiling you are basically correct, it isn't doing a lot of good, if any.

Old 02-14-18, 02:01 PM
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By code the division between conditioned (heated/cooled) spaces and unconditioned (not heating/cooling) spaces must be insulated. Your crawl space may be warm because of heat escaping from your boiler but it's technically not a heated or conditioned space so it's treated just like any other crawlspace which is usually cold and damp.

Have you actually measured the temperature inside your crawlspace at different times of the year? A 50f space may feel quite warm if you've just crawled in from 10f outside. You still would want the insulation as 50f is still less than the temp for the heated part of your house and would make the floor feel cold under foot.

Then, it makes you question why you are loosing so much heat from your boiler. You're trying to heat your home not the crawlspace so most of that heat is just wasted energy.
Old 02-14-18, 03:10 PM
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Hi Bud, the floor is concrete (although kind of crumbling in spots) and no vents.
Old 02-14-18, 03:17 PM
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The temperature inside the crawl space during the warm months when the boiler is not running (or almost not running) is pretty much the same as the basement (which is finished and at the same level adjacent to the crawl space -- 66-68 degrees). In the winter, on the coldest days, I never actually measured the temperature, but I would think it's probably in the 80's. I never thought that there was an inordinate amount of heat escaping the boiler. It will always give off some heat, plus all the pipes going through the crawl space.
Old 02-14-18, 03:55 PM
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Given that you have an unintentional source but source nonetheless of heat in the crawlspace, I would remove the ceiling insulation and insulate the walls instead. Additionally, I would look to open the space to the house air, if reasonably possible.

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