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PEX in Return-Air Ducts - Does Code Allow?

Pidge
Pidge Member Posts: 18
My home's 2nd floor east wall is canterlevered over the 1st floor wall. The overhang is about one foot. This east wall includes two bedrooms, each with a single triple pane window, facing the street. The plan is to install radiant panels under each of the two east facing windows.

See the attached drawing.

I'm converting from forced-air to radiant heat, and the return-air duct vents are on the east wall. The heat register is on the inside-west wall of the master bedroom, and on the shared north wall near the Southeast Bedroom's door - not the best for comfort. But running the warm-air ducts out past the first floor to reach the 2nd floor wall would be a big efficiency hit.

Running the pex from the basement thru the air-return ducts to the east wall will be much easier than any of the alternatives I can think of.

Is this code-compliant if I maintain the furnace for emergencies (like if the boiler shuts down)?

If not code-compliant, will decommisioning the furnace make it OK to use the return-air duct for a pex chase?

Thanks,
Pidge

Comments

  • Ironman
    Ironman Member Posts: 7,363
    No on both counts. I don't know what code is used in your jurisdiction, but every mechanical code that I'm aware of prohibits it.

    If the furnace is decommissioned, what's to prevent it from being recommissioned after the inspection?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • JohnNY
    JohnNY Member Posts: 3,226
    @Ironman
    Isn't there a "plenum-rated" designation for some materials to pass through an air conduit?
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
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  • MikeJ
    MikeJ Member Posts: 103
    I would say you need to check for your area, I have seen electrical wires cutting through return air chase, they had to make sure it was sealed.
    Other day went to look at a basement remodel. They had recess lights in the return air. Right away ask, you pulling permits for this job he said yes already had the electrical inspected. the lights were installed, he said yes.
    I think its something that varies
  • Ironman
    Ironman Member Posts: 7,363
    Yes, there's plenumn rated thermostat cable, but I'm not aware of any plastic pipe that's rated for it.

    If someone knows of any, please enlighten me.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,405
    As far as I am aware running through supply or return ducts with piping or wiring is a no..no.

    Return air plenums are a different story. Anything installed in a plenum must be plenum rated or made of metal (no burn..no smoke).

    If the furnace is decommissioned and removed then I would think running through the duct wouldn't be a problem
  • hvacfreak2
    hvacfreak2 Member Posts: 500
    If it's a straight shot it may be possible to install a sleeve of say 3 or 4 inch round sheet metal pipe through the duct that you could run the tubing in. Also the chase area may be somewhat larger than the duct so there may be some easier opportunities in that area. Also keep in mind that whatever you do it's best to close chase penetrations as tight as possible. Good luck with the project.
    hvacfreak

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