I am preparing to build a house that was designed with radiant heating. I will often leave the house for the 4 coldest months (it can get to -20F). I am concerned about problems with the radiant heat in an empty house that is exposed to that level of cold. I am considering a hot air system as a "safety" measure. Comments and opinions would be welcome. Thanks

I'd be concerned with just the condition of the construction materials being subjected to minus 20 degrees and then thawing.

Nothing can happen without power to operate the controls of whatever heating system you would have, unless it is a self-generating control system with fuel that can operate at such low temperatures, which doesn't include bottled gases or oils that gel.

Gas or oil heat requires maintenance to assure that there will be ignition, and even then, that can fail even though customers do the unusual by having seasonal preventive maintenance.

A secure electrical source would be required. If that wasn't available for some time, but can be assured to be off for only a short time, I'd install electric radiant heat in the same surfaces as the water radiant during installation to assure a backup. That would be a way to assure that the electric source could heat the radiant surfaces enough to thaw the antifreeze gel after a problem.

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Yes, you really have to find out the MAKE and MODEL to get good answers. There IS more than one machine made.