You could install a few fire dampers where the space transects the floor or
other places that make sense.

http://www.ul.com/regulators/dampers.cfm

Aside from the fire issue, leakage of the hot air out of the cavity might be
a concern for efficiency. Use of wall space for cold air return is common.
The under stair space in my prevoius 1973 home was used for cold air return
but a seperate return was used for the second floor.

There is nothing requiring you to change anything.

wrote in message
oups.com...
I've been doing a lot of poking around in my recently purchased house
in preparation for some major wiring work (the house has the original
1948 wiring, and I'm going to be adding a lot of up-to-code circuits).
The house is a 1.5 story with a finished attic. When I took off one of
the floor heating vents in the attic (forced-air heat) and shone a
light down the opening, I discovered quite a bit of electrical wiring,
including a junction box, visible below. As far as I can tell, attached
to the box is a wall light fixture in a room on the main floor.

I haven't done a lot of further investigating yet (I didn't have a
powerful enough flashlight), but it looks like it might be the case
that the ducting is not continuous from the basement to the upper floor
- the whole section of wall between the two joists is being used as the
duct. This is obviously very bad - especially considering the
electrical wiring in the space. I'm planning to replace the wiring
anyways, so it won't be a problem, but I should do something about the
duct. What options, short of ripping up a section of wall on the main
floor, do I have? My fiancee is not going to be happy if I tell her
that we have to rip out a section of wall, though if that's the only
option, I guess I'll do it (at least that wall only has paneling, not
drywall).

It looks like the wiring is original, so that means that either someone
was careless at the time of construction, or some HVAC person did a
crappy job when adding a vent to the upstairs.

Any tips on how I should handle this? Thanks in advance.