> If you ever do have a fire, Plenum wire will not
> release poisonous gas into the air and hopefully allow you to escape the
> building relatively unharmed.
>

Hah!  I'm sure your going to be really worried about what fumes may be
coming out of the furnace vent, if you have a fire in your house.  I
might be more concerned, say, with the fumes coming out of the
couches, or PVC pipe, or 1 million other things that make up a house
and release all sorts of noxious things when they burn.

I would tend to try to keep wires routed like this in the cold air
returns,  rather than the heat lines, to minimize the risk of them
melting :)