Protecting pipe from freeze in cold attic

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openhand

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Hello to all, I'm building a bathroom and pulling water from the main house to a barn loft where there will be heated, insulated space in the new bathroom. The problem is I must run the supply thru an unheated attic (I'm in Vermont), where the temps are identical to outside. There will be around 15 ft of run that will be vulnerable and I'm wondering what the best strategy would be for keeping the pipe from freezing. I'm planning 3/4 pex, which will be split into hot and cold once it arrives to the bathroom area. So far, we've thought of creating a chase with 2" foil faced foam that goes thru the uninsulated space, but I still think it will need to be heated inside somehow. The run passes thru a utility room with a forced hot air furnace and I was considering tapping from the plenum with a very small duct (2"?) and feeding some hot air into the chase whenever the heat kicks on. The other idea is heat tape, but how permanent and reliable is heat tape? Another thought is to just open the end of the chase to the heated utility room and let the warm air move thru the chase without the pressure of tapping from the plenum One problem with this may be that the pipe runs downward away from the heated utility room thru the unheated attic space, so convection won't be on my side. . Any other ideas? What have others done that has worked? Thanks, CT
 

Jadnashua

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Is there heated space along the entire area beneath the run? If so, and the pipe is run along the ceiling above, and well insulated above it, it should be okay UNLESS you heat goes out. Not all insulation is created equal...for example, fiberglass is a great air filter if there is air movement. Something like blown in cellulose is better at insulating and blocking air movement which is death to water pipes. A small pump to recirculate the water should keep it above freezing as well, maybe tied into a thermostat so it only runs when the temp drops. Again, though, if the power goes out, all bets are off. The only benefit with pex in this instance is that if there are no fittings in the run, the tubing itself will stretch enough without damage if it does freeze...fittings, on the other hand, are likely to fail.
 

Terry

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Get the pipes as low as you can in the attic, normally on the roof rafters, the parts that hold the ceiling drywall below.
Remove the insulation below the pipes or tubing, Then put insulation over the pipes, trapping whatever warmth there is that is escaping the home.
I do not put any insulation between the pipe and the ceiling.

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openhand

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Is there heated space along the entire area beneath the run? If so, and the pipe is run along the ceiling above, and well insulated above it, it should be okay UNLESS you heat goes out. Not all insulation is created equal...for example, fiberglass is a great air filter if there is air movement. Something like blown in cellulose is better at insulating and blocking air movement which is death to water pipes. A small pump to recirculate the water should keep it above freezing as well, maybe tied into a thermostat so it only runs when the temp drops. Again, though, if the power goes out, all bets are off. The only benefit with pex in this instance is that if there are no fittings in the run, the tubing itself will stretch enough without damage if it does freeze...fittings, on the other hand, are likely to fail.
Great thought on fittings, there's a way to keep them out of the most vulnerable part of the run. No there's no heat under the part I'm talking about- stone cold both sides so no way to capture heat from below (it's a barn space) Still collecting thoughts but I'm also thinking of opening the bottom end of the run to the heated space below (heated space underneath first 7ft or so) and letting it convect along the run, which will rise about 4ft over about 15ft.
 
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