Wiring Through Cold Air Return Duct

sf340dvr · Joined: 05 Jul 2005 Posts: 57 Location: Appleton, WI

I have to run some wiring through some floor joists in an older home. My question is this:

How should you route wiring through/around a cold air return for your furnace?

The cold air return is just a joist cavity that enclosed with sheet metal. Can you route NM right through it, does it need to be in conduit, or do you have to go around it by just stapling it to the joists on the outside?

Thanks for any help! Very Happy

jholmes · Joined: 23 Mar 2006 Posts: 80 Location: Eagan, MN

There are a couple of things that you could do, but need to aske one question - How are the floor joists going to be finished off from below? (sheetrock, acoustic, etc.)

sf340dvr · Joined: 05 Jul 2005 Posts: 57 Location: Appleton, WI

It's in the basement in our home, and I'm not planning on finishing it of right now. However, in the future, I might put a acoustic ceiling in, so I can still access the mechanicals.

Was hoping that I could just go under the duct and staple it to the bottom of the joists, but I don't know if this is allowed under the NEC.

jholmes · Joined: 23 Mar 2006 Posts: 80 Location: Eagan, MN

The NEC 2005 does have an exemption which allows you to route NM through a cold air return that is an enclosed stud/joist cavity, but it can only go through perpendicular (through at a right angle, not down the cavity). The fear is that overloaded wire heats up and catches the sheathing on fire and caustic fumes get in the environmental system through this cold air return. This exemption may not be allowed in your area! You need to check local codes, and anytime you do electrical work, you need to get a building permit and have inspections done! Your local inspector will know how it should be done.

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