What level of heat is recommended in an unvented crawlspace?
My project has 2200 sf crawlspace, 2/3 of which is 18″ minimum and the rest on a down slope having a height up to 12′ and which will house a water heater and furnace; and it has a 12″ thick structural mat foundation., This seems like the ideal application for a conditioned crawlspace so that I can run forced air ductwork and piping, since there is not an attic. There is less exterior wall than there would be floor area to insulate, and just as your 2011 article says, the insulation would eventually fall out. Another plus, the floor would be warmer and I won’t have to insulate the ducts and pipes, will I? And if the ducts leak a little it goes to good use, sort of.
Per your post the IRC calls for either of two options, the mechanical exhaust with a transfer grill from interior, or a register in the crawl space with some grills to exterior. The mechanical sub says the crawlspace air should not be returned because it would pick up gas and basement odors.
Are the minimum air changes assuming a delivered air temperature, or a maintained crawlspace temperature?
In my fairly mild Zone 3B (Calif Zone 12) is it necessary to insulate the slab and foundation walls as if it is occupied space, or is it enough to insulate the cripple walls (perhaps with Thermax which you mentioned)?
If the air is exhausted, how does one control the amount of conditioned air lost?
If I have a hole to the exterior for exhaust, how well should the cripple walls be sealed?
Would I need a vapor barrier and gyp on the cripple walls to keep condensation off the sheathing, or can it breath back to the interior?
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