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Louvered step lights are common but all that I've seen are decorative and not functional vents.

I'd like to install actual louvered registers on the side wall of my stairs and install low voltage lights in them so that my stairs are lit while at the same time allowing ventilation for the storage closet under my stairs.

Is this allowed? I know I can't have lighting inside HVAC but I'm not sure if this applies because I don't know if louvered openings between rooms (no forced air) constitutes HVAC.

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Not for ducts

The rules about wiring within HVAC ductwork are extremely stringent -- this is not due to anything related to voltage (i.e. shock hazard), but the potential for wiring insulation to overheat and smoke folks out. I'm not even sure if you can run fiber optic cables through HVAC -- even that may be verboten.

But for a louver between rooms, this should be OK

However, since this is a louver connecting two rooms directly (no duct involved), you can put a low voltage luminaire there. Either way, the precautions are the same: I'd use a type AC or type MC cable without an insulating jacket here, either that or a metal conduit wiring method, with the luminaire mounted to a metal box and using integral LEDs (vs an incandescent or halogen light bulb). This minimizes fire and smoke risks.

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  • Yeah, I guess the catch here is whether an open louver between walls counts as hvac
    – Matthew
    Mar 17 '18 at 3:42
  • You can run Ethernet in ducts but it has to be plenum rated. Plenum rating is a fire rating and restriction of material regarding burning emissions. I'm not sure if electrical wire comes in plenum rated.
    – Machavity
    Mar 17 '18 at 4:08
  • @Machavity -- not in an actual duct, save for short lengths to things that are actually part of the HVAC system, see 800.113(B) for details
    – ThreePhaseEel
    Mar 17 '18 at 14:27
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You see this more in a commercial buildings where the area above a drop in ceiling is usually a return air plenum. You can run low voltage cable (50 volts or less) in these ceilings as long as the cable and all of its appurtenances are plenum rated.

This is not really an NEC regulation but a Fire Code regulation. I hesitate giving this information out to a DIYer since it can get a little complicated and caution must be used when selecting material and installation. I would advise that if you want to do this, do some due diligence and talk to your AHJ and perhaps a few professionals so you can understand what you are doing and prevent a smoke hazard in you residence.

How do you know if you are getting the right material. It will be specifically listed and of course it will be expensive.

Hope this helps.

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