# How To Insulate Gas Pipe?



## Starlight (Sep 30, 2010)

I've run black pipe (steel) through a 2.5" hole in a wooden joist. The pipe is 1" or 1.25" (id). Should I just stuff the hole with fiberglass, or might the fiberglass abrade the walls of the pipe. The joist is between the unheated attached garage and a first floor room. On both sides the pipe will run between joists in the ceiling and be covered with drywall. 

Other choices I've thought of: 
Great Stuff - might the chemicals react with the steel pipe? I could put tape on the pipe first. 
1" foam pipe insulation, than fill the extra space with spray foam or fiberglass. 

I don't think any choice would be that expensive, so I'm more interested in the best thermal seal. 

Thanks for your help, 

Paul


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## Windows on Wash (Aug 30, 2011)

Foam it or use another type of sealant.


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## SPS-1 (Oct 21, 2008)

The 1/4" per side gap is too small to matter as far as insulation goes. You will get far more heat transfer through the actual steel of the pipe. But you need to stop the airflow though the hole. Fiberglass will let air pass, but if you have some lying around, why not, then caulk. Great stuff would work, but can make a terrible mess. I would just caulk it on the outside with acrylic caulk.


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## Mystriss (Dec 26, 2018)

We were told to use a bead of silicone around our exterior pipes then insulate inside.


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## Yodaman (Mar 9, 2015)

Duct seal, it is like playdough, but sticky and water resistant for out door use such as this.
https://www.lowes.com/pd/Gardner-Bender-16-oz-Duct-Seal/4595233


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## Starlight (Sep 30, 2010)

Thanks for all the replies. Good point about fiberglass not stopping air infiltration, as this is an important factor since the pipe is going from unheated garage to heated room. Foam sealant would work well, but as SPS-1 says, it can make a big mess for such a small project. I did not think about the playdough-like duct seal - I have some Moretite lying around somewhere.


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## NotYerUncleBob2 (Dec 29, 2017)

Starlight said:


> I don't think any choice would be that expensive, so I'm more interested in the best thermal seal.


It's the air sealing that is key in this scenario. R value doesn't matter much for such a small space.


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