Radiant floor heat questions


Old 07-17-07, 06:33 PM
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Radiant floor heat questions

I'd like to install radiant floor heating in my soon to be tile family room [concrte slab underneath, so it's always cold] while the floor is up . The area is roughly 20x20 . Will one 12/2 feed be ok? I am unsure if these are 120 or 240, nor the size wire required for such an area ....

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Old 07-17-07, 07:52 PM
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If you go to a radiant heating website some will calculate how many watts of heat you need. If not you should be able to find out how many watt/foot the mat takes. I think I used www.nuheat.com
Old 07-18-07, 08:06 AM
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> [concrte slab underneath, so it's always cold]

I would recommend that you also put down cork thermal break to reduce heat loss through the slab.


> The area is roughly 20x20 . Will one 12/2 feed be ok?

400 sq. ft. No. You'll probably need (2) 15A 240V heating systems or (1) 30A 240V heating system. This is based on a calculation of 15W / sq. ft. which is the maximum allowed for indoor floor heating. Most heat cable manufacturers recommend that you use the maximum heating over concrete slab subfloors. This yields 6000W of total floor heat, 25A @ 240V.

I believe that they only make 15A thermostat/controllers and heat cables off-the-shelf. A 30A system would need to be custom. So based on that I think you need (2) 12/2 runs to opposite sides of the room and (2) 15A double pole breakers. However, you should definitely locate a heat cable system manufacturer and design to their specs.


> I am unsure if these are 120 or 240

They make both, but you should use a 240V system for the square footage you have.

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