I noticed that there is significant heat loss at my bathtub drain. If I put my hand above the bathtub drain, I feel an icy draft.

The plumbing is directly under the bathroom, in an unfinished basement.

Here's what I have thought of so far:

  • Put a stopper in the bathtub when not bathing

  • Put foam sleeves around the pipes in the basement

  • Perhaps something in the plumbing arrangement in the basement needs to be re-done in some way

Any thoughts?

P.S. I chose "energy efficiency" as a tag because I couldn't find "heat loss."

Update: I nosed around downstairs while the hot water was running in the bathtub, so I could be sure I was looking at the correct pipe. There is a U a little below where the pipe comes out of the bathtub. Then there's a straight stretch of approximately 6 feet. Then there's a T and the upper part goes up and out of the house. That portion feels very cold. So apparently I feel a cold draft at the bathtub drain because cold air from outside is coming in through that pipe! Is that unorthodox?

Second update: Can I use "dryer vent seal"? I found a type that is sold at the DIY stores and also a homemade one.

Third update: I read about the "AAV" but wasn't sure if I was on the right track.

Then I read about what might be my situation:


  1. Crawl under your bathroom to look at the drain assembly from underneath.

  2. Patch the hole with pieces of foam board that’s cut to fit around the pipes. Screw them in place.

  3. Then seal any gaps with spray foam insulation ($8 per can).

  • 1
    Is there an air vent anywhere on top of a drain pipe in the basement? – Mike Waters Mar 2 '19 at 0:46
  • 1
    @MikeWaters - Not sure. I will try to figure that out. Suggestions on how to go about that? Also -- what will you say if the answer is yes, and what will you say if the answer is no? I'm sorry, I'm not very experienced with DIY stuff yet. – aparente001 Mar 2 '19 at 0:47
  • Is there a floor drain in the unfinished basement? If so, the water in the trap may have evaporated. – Mike Waters Mar 2 '19 at 1:51
  • 2
    do you hear any sounds coming out of the drain? – jsotola Mar 2 '19 at 4:34
  • 2
    Sounds like your drain pipes should be frozen, what keeps all the pipes down there from freezing? And if air's coming up out of the drain, does it smell like sewer gases? – Xen2050 Mar 2 '19 at 6:46

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