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I have Pex pipes. My issue is freezing pipes and tankless hot water heater on the north side of my house (built in 2009) where my master bath is (the tankless is on the outside of the house on that north wall). The house is 2-story.

The builder unfortunately ran the Pex in the attic and they sit about a foot from my continuous soffits, so cold air blows in there all the time in the winter. I'm stuck with it being where it is, so I don't need comments about it being in the wrong place. Also, my toilet lines in my Master Bath run on the north wall.

I'm in Texas, but when the temps gets in the teens, my pex lines coming into the toilet always freeze. I trickle water in the sinks/tub and they are fine (but only if I trickle water). Also, if it is in the teens for 2 or 3 days, my tankless water heater gets frozen (the lines into the tankless freeze; although this last time it froze on up into the unit).

I have had holes drilled in my brick on that wall to blow in foam insulation in the walls on top of regular insulation. Didn't help.

I've had foam insulation things put around the Pex in the attic. Didn't help.

I have had a company blow in a ton of loose insulation over the Pex in the attic...didn't help (but I think the wind blows it back off).

Bottom line, the pex continues to freeze and I can only surmise it is because of them being in the attic in the location they are in. I can't move them. I've never had the pipes burst, but eventually, I'm afraid they will - I would image pex can only freeze/thaw so many times. I don't like being without a toilet during cold snaps, and having my tankless freeze is costly. (It cost be $475 the last time I had a plumber out to thaw it out, but it could be even more costly if I didn't get it thawed). Builder will NOT help.

Looking for suggestions to keep the pex from freezing in the attic, as that might solve the freezing pipes to the toilet and even possibly solve the frozen lines to the tankless.

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  • I assume that the water in the water heater itself did not freeze. Does it have an electric heater in it? Electric heating tapes should work to keep pipes from freezing.
    – Jim Stewart
    Feb 16, 2017 at 23:52
  • I have not used heat tape on pex but that may be an option, when I have water tanks outside I have installed a small cadet heater in 1 home where a light was not enough but usually a 250w heat lamp has been more than enough to keep the pump room warm. Trickling water on the hot tap below the turn on point may also help my Bosch aqua star won't turn on until there is more than a trickle. Better waste a few $ on water than a bunch on replacing the unit.
    – Ed Beal
    Feb 16, 2017 at 23:53
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    @Jim read close, she said the heater freezes and costs $475 everytime. It's a gas unit, that's the only conceivable reason to put one outside. OP should have a talk with their city inspector and ask whether or how this passed inspection. Since it sounds like a new home, this is on the builder, who should have known better; OP shouldn't be out a dime since this is a home defect, and a dumb one at that, and OP paid in good faith for a 4-season house.
    – Harper - Reinstate Monica
    Feb 16, 2017 at 23:56
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    Is this a brand new house, or a place that's been recently remodeled, or has it been this way ofr a while?
    – ThreePhaseEel
    Feb 17, 2017 at 0:22
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    I assume that the PEX pipes in the attic run across the tops of the ceiling joists. The piping should be covered with a rigid U or V shaped cover reaching down to the attic side of the ceiling drywall which excludes insulation so that heat will flow from the house into the space around the pipes. The outside wall containing the piping to the toilet will have to have temporary insulation placed on it on the outside. This could be, for example, fiberglass bats in a sort of box propped against the wall. The box could have foam rubber weather stripping along the edge to seal.
    – Jim Stewart
    Feb 17, 2017 at 14:04

2 Answers 2

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To prevent freezing of the PEX water lines in the attic I think you should consider covering them with a cover that would allow them to be kept warm from the space heating of the house. Insulation over this cover would prevent heat escaping into the attic. The cover would go all the way to the attic side of the ceiling and insulation would be removed from under the cover to that heat flow from inside the house can keep the pipes warm.

You report that putting foam tubing over the PEX lines did not work. The next thing to try would be electric heating tape, but covering the lines would seem to be a more permanent solution. I have never heard of covering of the water lines being done, but I have never heard of freezing of plumbing on the scale that is occurring in your house.

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    Right. Carefully-placed batts or blown insulation resting on poly over the pipes, with nothing underneath, would resolve this in a hurry. The only question is whether there's room for that if they're located way down by the truss heels.
    – isherwood
    Feb 17, 2017 at 17:52
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This isn't just about insulation but about insulating the right way. Simply you need to make sure that the PEX lines are on the bottom of the soffits with no insulation between them and the living space. Then you need to insulate just above them. For this in Texas I would suggest ROXUL - about a foot thick over the lines - then blown in over that.

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