Crawlspace insulation
How strong a heater do we need for our insulated crawlspace?
Please help! We just put crawlspace insulation into our 3 ft max. crawl space - Walltite spray (the blue stuff). The floor has heavy gauge plastic and all was done very well indeed. Now my husband just bought 2 forced air heaters, 4800 watts 16382 btu, and 240 volts to heat the crawlspace which measures 30 ft by 40 ft by 3 ft at the highest.
They seem like overkill as the problem is only cold floors. There is no insulation above the crawl space. Can you recommend some other type of heater? How many do we need for those dimensions? There is still time to return the "monster heaters"....
Answer from Green Energy Efficient Homes
It's hard to figure out how much of a heater you would need without knowing how cold it gets in your area in winter and exactly how well insulated and sealed the crawl space is. An engineer or HVAC technician on site might be able to do a thermal load calculation for you to figure out how much you will need.
The more you can keep the cold from outside out of your crawl space (which it sounds like you have already done with your crawlspace insulation), and the more you can keep the cool of your crawlspace from cooling your ground level floor, the less need you will have for a crawl space heater. If the floor has air gaps, close them (but don't use a vapor barrier between the crawl space and the house). If the floor is uninsulated, I would suggest insulating it. We have 8" joists under our kitchen extension and they are insulated with pink fiberglass insulation, which works out to about R24, and with the relatively well insulated crawl space already keeping most of the winter cold out, the floors get cold but do not cool the room itself.
Also, don't forget above-floor insulation - carpets, throw rugs, and slippers. I even wear my summer sandals in the winter because it insulates my feet against the cold floor above the crawl space, and that makes enough of a difference that I don't need a heater down there. Of course you have a much bigger crawl space so this may not be enough, but the more you can insulate, the less you'll spend for the rest of the life of the home on heating the crawl space.
Remember, in all but the coldest of climates or the largest of crawl spaces, adequate sealing against moisture, as described in Crawl space heater, and proper crawlspace insulation, should be all you need - crawl space heaters are really a last resort for people who can't find a way to keep most of the cold outside the crawl space. Proper sealing and insulation costs more up front and keeps on saving you energy year after year; a crawl space heater may be cheaper at front but you keep paying the bills every time the thermometer dips.
You might find an infrared heat gun helpful as well, which you can use to pinpoint specific areas where cold air may be leaking into your crawl space from outside, or from the floor into your living space.
Finally, it may be better to start with lower capacity heaters and add more of them if it proves not to be warm enough - unless the high-capacity ones you have bought are substantially cheaper per BTU of output or are especially designed for heating a crawl space.
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