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Pex Through Fire-Rated Ceiling

I wanted to see if anyone has experience with fire-rated ceilings. I'm working out an installation of a single-zone radiator-based radiant heating system. I'd like to put a wall-mount boiler in a shared laundry room that the City requires to have a 1-hour rated floor-ceiling assembly separating it from the unit above. You can normally make a limited number of membrane penetrations through the 5/8 type x drywall for pipes and electrical boxes if they are properly caulked and within limits, etc. But if I have 9 radiators on a home run setup, that's 18 penetrations through the membrane, which I think might ruin the rating.

Does anyone have experience making penetrations for 1/2 inch pex and sealing around them with intumescent caulk? My backup thinking is to place the home run manifolds in a remote location from the boiler so I'm only running a single supply and return into the fire-rated assembly, or alternatively doing reverse supply/return piping with diverter tees for the same outcome. Although the Coffee with Caleffi I watched on proven piping systems was selling the home-run setup very hard :smile:


  • hot_rod
    hot_rod Member Posts: 16,327
    Pex is used for fire protection piping, it has ratings listed here for Uponor brand.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • OaklandNS
    OaklandNS Member Posts: 50
    Thanks, hot rod. Looks like the listings for Uponor-A are pretty specific in terms of the assemblies where its approved. I took a look at some of the caulking manufacturers, and it looks like they have UL approval for PEX through fire-rated membranes if you pack the annular space with mineral wool and caulk.
  • Zman
    Zman Member Posts: 7,330
    edited January 2019
    The way I have dealt with this in the past is to work with tech support or your local rep from the fire stop manufacture. 3M and Hilti are both big players. If you tell them what the rating needs to be and what you are running through it, they will provide a detail that you can show the AHJ. It is not a bad idea to have the detail approved before doing the work.

    I think that a small hole like that can be done with just intumescent caulk at a specified width. Make sure you double check that the caulking is compatible with the PEX chemically.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    EBEBRATT-Ed Member Posts: 12,016
    Your idea of mounting the manifolds remotely would limit the fire stop problem down to 2 steel or copper pipes.

    It makes a lot of sense to me
  • OaklandNS
    OaklandNS Member Posts: 50
    Carl, thanks for the tip on contacting Hilti or 3M. That’s a great idea.

    I talked to the inspector and he indicated that if I run the pex into the wall stud bay first, I can penetrate the top plate as much as I want if I protect the penetrations with intumescent caulk. I’m going to talk to him with a floor plan this week, so maybe I can get a drawing from 3m ahead of time.

    Othwerwise, remote manifolds will work. Just more pex, more drywall patches, and more work.
  • OaklandNS
    OaklandNS Member Posts: 50
    Just closing the loop. The inspector told me it was preferred to run the pex through the top plate of the wall into the floor joists and firecaulk the topplate penetrations. I pointed out that my joists are not centered over the studs, and swiss-cheesing the top plate wasn't a good idea. I showed him the detail from 3M linked below and he said that doing it that way directly through the fire-rated drywall would be just fine.

  • ratio
    ratio Member Posts: 3,185
    I've found that most inspectors are quite happy to pass the buck to something in print. You do have to make sure you do it exactly as the details shows, though.