PEX in Return-Air Ducts - Does Code Allow?

Pidge

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

Ironman

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?

JohnNY

@Ironman
Isn't there a "plenum-rated" designation for some materials to pass through an air conduit?

MikeJ

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

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.

EBEBRATT-Ed

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

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.