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Heat trap size (thermosiphon block)?

I was looking for this same answer and found some related information at the Oregon Certification for Solar Thermal Projects website as follows:

14. Anti-convective pipe loop or trap is required on the inlet and outlet of the storage tank. These loops or traps shall have a minimum 8-inch vertical drop to constitute an effective convective heat barrier. Heat trap nipples alone are not reliable in stopping heat migration, and will not meet this requirement.


  • Charles_8
    Charles_8 Member Posts: 74
    How tall should it be?

    I'm heating my hot water with the tankless coil in my 1-pipe steam boiler, but pumping it with a Taco 006B circulator to a 40 gal. storage tank. I installed a check valve to prevent extremely hot (during heating season) water from the coil from thermosiphoning backwards into the top of the tank. Sometimes the check valve flap sticks open from "crud", as the city water is rather hard. This is not only annoying due to the scalding temps but also because it can get hot enough to trip the high-limit switch on the tank thermostat.

    So what I think will help is a heat trap loop somewhere between the coil, check valve and the pump outlet as another thermosiphoning preventer.

    How tall should the loop be? Does it have to go all the way up above the highest point or down below the lowest point in the closed circuit (of pump, coil, tank) or will a foot or two as it comes off the coil be sufficient?

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