Cables in a duct

August 31, 2006 10:10 AM

Fire Hazard Filter: I am thinking of running a network cable through a section of HVAC ducting in my house (~6' stretch relatively far from the furnace/AC unit). Will this be a fire hazard in the winter, when the furnace is on? I don't really care about thermal wear on the cable itself.
posted by Krrrlson to home & garden (6 answers total)

Local building codes may well not allow this, but practically I can't see that it would cause a problem if you used plenum rated cable.

"Plenum rated cable has a special insulation that has low smoke and low flame characteristics. Plenum cable is mandated to be installed in any "air handling" space." (quote from this page)
posted by Quinbus Flestrin at 10:16 AM on August 31, 2006

You must use plenum/riser cable (depends on how much vertical you plan to do). Your homeowners insurance could be voided if you don't. Furthermore, the gases given off by non-plenum/riser cable are very toxic and could kill you in a fire before the fire reaches you.

In commercial installation / cinder block houses (if they exist) you would, in my locale, be required to use plenum/riser/FT5 in anything but open air space. In a house, since your home (mostly wood, sometimes metal studs) is more likely to burn than the cable, the fire rating isn't as important. It's how toxic fumes from it will be that matter, as the inhabitants are likely to be gassed by them.
posted by shepd at 10:23 AM on August 31, 2006

I've done this before with no problems.
posted by dead_ at 10:28 AM on August 31, 2006

>Will this be a fire hazard in the winter, when the furnace is on?

Oh, I didn't answer this, sorry. No, neither cable is going to burn from your furnace, unless you install it inside next to the burner. The PVC jacket on cheap cable is going to be reasonably solid up to about 85 celsius. At 85 celsius you probably aren't going to be in the house. And it's unlikely you will ever dump enough current into that wire (even with a dead short on it) that it will heat up enough to reach ignition (WAY higher than 85 celsuis). Note that at higher temperatures on cheap PVC cable you could be at risk of minute dioxin exposure. Nothing I'd worry about, but it's up to you. :-)
posted by shepd at 10:49 AM on August 31, 2006

A random thought: If this is a short segment of a longer run, you might be able to run the cable through some sort of conduit or sleeve where it's going through the duct, in order to meet fire/insurance codes.
posted by hattifattener at 12:17 PM on August 31, 2006

There are teflon-jacketed (PTFE) network cables available for just this fire-resistant purpose.
posted by cardboard at 1:13 PM on August 31, 2006