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What kind of provision would we need to protect an under-slab radiant heat system from freezing when the power fails?
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There are anti-freeze's available for hot water heating systems. But are your domestic waterlines installed so they can be completly drained to prevent freezing? Most arn't, even though most codes require them to be so installed. I install heating systems in remote areas of B.C. and very seldom use anti-freeze as most homes have back-up wood heat or a back-up generator as in my home (which incidentally has been in use for the last three days thanks to a heavy snowfall on Thursday and Friday taking out a few power lines)
The reason I don't like to use anti-freeze is it reduces the life in some of the components of your system and it needs to be replenished every couple years something most homeowners are going to forget about. And in most cases a year round residence is never going to be allowed to freeze inside. Not to mention the Mass of a 4" slab is going to take a while to lower in temp.
*Unless you are talking about a snow melt system and the slab is outside, no provisions should be necessary. Ground temps (below the frost line in the lower 48) is between 52 and 56 deg F. If the slab is not directly exposed to outside air temps, wind etc, it will not freeze.
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What kind of provision would we need to protect an under-slab radiant heat system from freezing when the power fails?