What caulk to use for plumbing penetrations?

I have forced hot water heat, and I want to seal up the gaps where the hot water lines penetrate the basement ceiling/first story floor.

I figured that I would use Great Stuff expanding foam. Their web site states that "Foam is flammable until cured", but the can says "Cured foam is combustible and may present a fire hazard if exposed to flame or temperatures above 240 degrees Fahrenheit".

I assume that temps will stay below 240 as long as long as the house isn't on fire, so is this the right product to use on my hot water lines? I basically just want to stop the cold basement air from making our bathroom into an ice box.

Thanks,

PDBS

You can buy a fireproof caulk for this purpose at the big box stores.

The simplest and safest thing to use is backer rod. It's a foam material that comes in a variety of diameters. You can always caulk over it if you want, but you may not need to.

foam

I doubt that the foam would burst into flame at 240 degrees, and your heating pipes should not, and probably could not, get to that point if everything is funcitioning properly. But if the temperature did get to that point, you would have more to worry about than the foam because your boiler would be on the verge of exploding.

Thank you all! Of all the searching that I did about info on caulking plumbing penetrations, I never once found any info about fireproof caulk.

This article agrees with the advice here, which says I should be using ASTM-E136 standard fireproof caulk with foam-rubber backer rod for larger voids. Looks like I need to head over to Home Despot to pick some up...

PDBS

I think the fireproof caulk is only needed if you're penetrating firestop barriers and other exotic things. But, it's not terribly expensive, and impresses the hell out of inspectors. I use it to seal up all electrical and plumbing penetrations. I think the Great Stuff would work OK In your application, but it will burn and produce toxic fumes in the event it does get ignited somehow.

Mikey said:

I think the Great Stuff would work OK In your application, but it will burn and produce toxic fumes in the event it does get ignited somehow.

Click to expand...

The "Great Stuff" is not so great to work with. It's extremely toxic until it cures, it's very messy and sticky, and you have to cut off all the extra that sticks out of the cracks.