“How to heat crawl space? – recommendation needed”

Photo by PoPville flickr user Mr.TinDC

“Dear PoPville,

I recently had the 3-foot high crawl space of our row home/3-unit condo building conditioned, with spray foam used on all perimeter walls, and then sealed the crawl space entrance as well as any vents, and added vapor barrier to floor. It was recommended that I add a heat source to the crawl space so that my floors are not freezing cold (I am in first floor unit above crawl space). Can anyone recommend a person to evaluation my situation and make a recommendation on how to safely provide heat to the crawl space?”

15 Comment

  • Pablo Raw

    2nd. to last parragraph of page 2 of this buildingscience.com/documents/bareports/ba-0401-conditioned-crawlspace-construction-performance-and-codes

  • I’m not a contractor, but I have watched a lot of Mike Holmes’ shows. If the crawl space isn’t heated, won’t that make a cold zone next to a warm zone, and cause condensation, mold, and rot? Seemingly the easiest solution would be to somehow allow your heat from the living space to transfer to the crawl space – via vent(s) or opening(s) of some sort.

    Also curious – is it a cement floor to the crawl space, or just vapor barrier over earth?

  • Don’t have an answer. But am looking to do the same thing to my crawl space. What company did you go with for the insulation, vaper, etc..? And were they good?


  • Shouldn’t the flipper have taken care of this? Seems like a glaring oversight.
    How expensive would it be to pull up your wood floor and install electric radiant heat?

  • I am in the same situation with our newly purchased rowhouse. Dirt crawlspace, no vapor barrier, one vent in the back, high humidity and cold floors. Who did you use for the vapor barrier and spray foam? Did you also bother with a dehumidifier? I have had no luck with anyone, besides pest control company, to return my requests for a quote.

    Do you have central heating with ducting in the crawlspace? That may provide enough heat to condition the space.

  • Wait…this thread raises a dumb question for me… We have a “semi-finished” basement, i.e. we put floating hardwoods on the cement slab at the bottom of our typical DC rowhouse basement. Does this mean we were supposed to put something else under there? It is pretty cold down there…

  • I’ve never seen a conditioned crawl space before, but it would have been nice at one of my college apartments that sounds exactly like this row home.
    A good HVAC installer should be able to vent some of the air from the apartment to the crawlspace. See the following from http://www.epa.gov/indoorairplus/technical/moisture/1_4.html on a couple of ways it can be done. It would help if you have a return vent in the crawl space.
    Several retrofit radiant floor heating methods are out there, but if you only want to raise the temp of the crawl space a couple of degrees, and not heat the living spaces above it, venting the living spaces to it may be the best solution. I think the radiant floor systems are more for heating a living space.
    Good luck. It sounds like an interesting problem. There’s always area rugs.

  • Don’t waste money on a heat source. Add insulation to the underside of the floor with a vapor barrier between the floor and insulation. This will separate your floor from the cold crawlspace. Your floor will be the same temperature as the room above and the crawlspace will stay cold.

    The insulation on the crawlspace walls does little or nothing since hot air travels up, not sideways. The vapor barrier on the ground helps control most moisture, but does nothing to insulate the space. The crawlspace is still cold because the ground of the crawl space is the same temp as the outside ground temperature because of conduction (for conduction think of the handle of a metal spoon in a pot of boiling water or block of ice cream).

    Instead of adding machinery to ventilate your sealed crawlspace, I would reopen some vents in the walls and let natural circulation take care of it. If you insulate the underside of the floor you will have established the crawlspace as outside the thermal envelope of your house. Don’t waste money heating/ventilating spaces outside your thermal envelope (porches, attics, crawlspaces, etc.)

    • I’m suffering from this same problem with a rental unit that’s making my tennants unhappy. Why would you place a vapor barrier between the floor and the insulation…wouldn’t that allow for condensation and mosture somewhere in the assr either eventually rotting a wooden floor or destroying the insualtion?

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