Thermosiphon to Prevent Freezing
I plan to build a detached garage with a guest apartment above. The apartment will be occupied ~90 days per year. I live in CZ 6 with a 99% heating temp of negative-18 F.
I plan to piggyback the plumbing supply lines from the main house. When the guest apartment is occupied in winter, the supply lines will be exposed to outdoor air temps when passing vertically through the (unheated) first floor of the garage.
My hope is to (1) prevent frozen pipes with as little complexity/maintenance as possible and (2) reduce hot water wait times in the guest apartment. The run from the electric tank-type water heater to the guest apartment will be about 50 feet (35′ horizontal, 15′ vertical).
Does it make any sense to create a passive thermosiphon loop in the hot supply line? Where the hot and cold supply lines pass vertically though the unheated garage, I will bundle the lines together within a well-insulated chase.
When the apartment is occupied, the siphon of hot water will warm the inside of the chase. When the apartment is unoccupied, I will drain all of the lines. During warm weather, I could turn on the supply lines but close the return hot water line, reducing wasted energy from the siphon (though increasing wait times for hot water).
Workable? Useless? Just use heat tape? Thoughts appreciated.
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