No experience. I would think the tankless system would be on 24 hours a day. Seems like a very big problem. I have a regular hot water tank and a pump to circulate the hot water. It works on a timer so I only set it to run a couple of times during the day - when we get up, bed time etc. - and when it is freezing I will run it once or twice in the early mornings on freezing days. (cold water return line helps here) Instead of a timer you could use a smart plug and your phone. I circulate back through the cold water pipe. Not a problem sine I do not run it all the time. But if I did it would be a problem as the water would be too warm. For your system you need a way to turn it off and on when you need it. Might take a minute or two to get hot water so you would have to turn it on before you needed it.
How are the pipes protected from freezing assuming the unit is mounted outside?
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