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Community and Q&A

How to Insulate Boiler Pipes in Kneewall Spaces

rzste | Posted in General Questions on

I have 2 uninsulated kneewall spaces in an attic, a slate roof, and a large amount of copper pipes from a hot water boiler running through the spaces, which feeds 2 zones. There are 3/4 in and 1/2 in pipes. There are a few large soffit gaps on each side where I can see sunlight outside during the day. During the winter, outside temperatures would get down to 0 degrees F, to -10 infrequently, maybe -20 would be the absolute lowest.
I am planning on getting some fiberglass? insulation and stuffing it in any openings  to prevent drafts. Regarding the pipes, my concerns are

1. Pipes freezing. I think the chance is low since they are hot water pipes but in case the boiler stopped working for some reason or if a tenant turned off a zone or there is a thermostat error, and then the time it would take to have it fixed.
2. There is no reason to heat the kneewall spaces and I’ll lose heat as the pipes are traveling through that space. I’d estimate maybe 30-40 feet of pipes, but some of them go into and out of the living space, so perhaps less.

What material would you recommend I use for the pipes? The big box hardware stores has self-seal foam insulation with R-values of 3.1-3.3.
a. Is this r-value/material sufficient?
b. Could it melt if the hot water temperature is too high? Not sure how high it gets but it is 160 degrees now.
c. Would mice eat it?

Later I’m going to see if I can get the floor and wall insulated to protect the living space. I figure if there are no drafts, the pipes should still be safe.
Appreciate any advice.

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  1. Expert Member
    BILL WICHERS | | #1

    Boiler lines, especially if this is a steam system, are typically insulated with a rigid fiberglass pipe insulation. This is a commonly available item at commerical supply houses, but I've never seen it in box stores. It's a yellowish rigid fiberglass insulation formed as two split pieces that fit over the pipe, with a white exterior wrap. You can get plastic elbow fittings (and others) for connections too. It's not particularly expensive.

    I'd try a local mechanical supply house and ask for this material so that you can do the job right.


  2. rzste | | #2

    Thanks. It is a modulating-condensing boiler, not sure if that is the same as a steam boiler.

    Is the rigid fiberglass pipe insulation superior to foam insulation to prevent the foam from melting, or will it conserve more heat? And how do they compare to each other to prevent freezing?

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