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rtoni 09-10-2008 11:21 AM

thoughts on crawl space heating

I have a summer place / camp /cottage with new addition (work in progress) built over crawl space - approx 1000 sq ft - concrete floor (rat slab) poured over poly, outside walls insulated with 2" rigid styrofoam, rim / band area to be insulated (soon) with either batts or spray foam (depending on $ for foam option).

upstairs is to be heated with an airtight wood stove which will be my primary heat source - no forced air or ducted heat planned - researching a direct vent propane ductless system to complement the wood heat - just enough to kick in and keep things warm in the wee hours when the fire dies down. the space is about 60% open concept - I'm leaning towards a unit like Rinnai's that apparently can easily fill the gap. no plans for A/C (place is on Lake Superior and tucked into a well treed spot - indoor summer temps rarely climb beyond 75-80 deg.) no plans for forced air or related infrastructure. Only ductwork is to feed the woodstove with outside air.

anyway, the idea is that enough heat from the living space will migrate (by design) into the crawl and work in conjunction with the geothermal from the ground to keep things down there from freezing / heaving.

I purchased a decent dehumidifier designed specifically for crawl spaces - which should keep it nice and dry, and even provide a tiny bit of heat itself from what I understand, in the process.

question is - if I do want / need to bring the crawl temp up a bit in the winter, and I don't have (or want) a forced air system to pipe in air, what options do I have? e.g. is there a smaller, reasonably efficient gas or electric boiler system that I could run in the crawl with a couple of short runs / rads along walls?

I may not need anything but if I do I would like to keep this simple

any thoughts appreciated.

sgthvac 09-11-2008 10:52 PM

Why not use electric heat tape wrapped around your water lines? Insulate the outside walls of the crawl and the dehumidifier with the heat tape should work fine.

Termite 09-11-2008 11:35 PM

In order to get away from the code requirement that you ventilate the crawlspace with outdoor air, the code requires you to run HVAC to it. Although the obvious issue is freezing pipes, the real issue is moisture mitigation year-round. You're halfway there with the slab and poly, which is half of the code requirement. The other half of the requirement is that you either have the crawlspace open to conditioned space, or you condition the crawlspace.

In most cases the best bet is to add a heat/cool duct run and a return to the crawlspace off of the home's system. Since that isn't possible you need to install a unit that will maintain a good temperature down there. That seems rather impractical to me. Have you considered insulating the floor and providing outdoor air vent openings to the crawlspace? As previously suggested, pipes can be kept warm with heat tape warmth devices.

My suggestion would be to contact the local building official to see what he/she is going to require and what they'll accept.

Marvin Gardens 09-30-2008 12:47 PM

Just get heat tape. It is set up to go on at about 39 degrees. Wrap all your pipes and then insulate over them. Check with the manufacturer to make sure they are the type that allow insulation going over them (most allow that these days).

My guess is that the geothermal heating from the slab will do just fine and the heat tape is just in case.

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