Burst Pipe Follow-Up: Closed Circuit Pipes
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Last month we explained how burst pipes can be prevented by letting faucets drip a little bit. This relieves the pressure, and even if the lines freeze, they are less likely to burst.
After that article, we were asked what to do to prevent burst pipes in closed circuit systems, like forced hot water.
At first blush the answer seems easy: make sure your heat is on! But in practice it requires some thinking ahead. Closed circuit pipes burst during vacancies when the heat is off. They can also burst when alternate heat sources like pellet stoves or fireplaces can drive a thermostat above the trigger point, causing the furnace and pump to shut off.
Take care with properties that have alternate heating systems and make sure that your pipes are circulating through a hot area. It's not true that moving water cannot freeze. Moving water can freeze solid. Think of any river or stream you've seen frozen. You must circulate the water through a heat source, whether that's the boiler or the fireplace heated room.
We're not sure that the heat from the fireplace would work its way back into the pipes. You might need to set the thermostat to 90 degrees while the fireplace is on to make sure the furnace keeps running, too.
If you expect a long vacancy, drain the closed circuit pipes and shut off the heat. If there's no water, it can't freeze. Some folks online recommend anti-freeze, but the volume required and the toxicity of antifreeze, especially to pets and children, make us think that draining is better.