I'm reinstalling the pipe insulation that runs from my central air conditioner condenser and I noticed there is no sealant as it enters the house.

I'm thinking foam wouldn't be great because the smaller line gets hot. Just a note that it does not have any insulation so I will not be adding any there.

What should be used to seal this as it enters the house?

HVAC lines

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    can't the foam handle the heat? you could pack fiberglass insulation and a metal mesh around the hole to keep out varmints.
    – dandavis
    Commented Jun 21, 2022 at 20:40

2 Answers 2


Thumb Gum and Duct Seal are two brands of putty to seal holes around lines.


Use some fiberglass insulation as you have some and be sure it supports the tubes so they do not rub on any hard surface. After that you can caulk it or whatever you want to use. The small line (liquid line) gets hot as it is the output of the condenser. The temperature will vary over time and temperature depending on the AC load and ambient temperatures.

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