Does anyone know what would cause this discoloration of the wall around the registers? There was some rust on the heat exchanger, could it be soot?
It may just be from dust in the ambient air. The discharge air from the register striking the wall creates a static charge on the wall which attracts the dust. Check the furnace filter and horizontal surfaces in th home for unusual dust accumulations.
Anything that you can see like that, is probably dirt, that has come through
the system, i.e. system not filtering well…I’d use general comments and
call it out as poor filtration, change filters more regularly, blah blah blah…
with exhaust coming from the heat ducts, there is a high probabllity
that the exchanger is cracked or the exhaust flue is blocked.
you can check the air quality at the registers, for Co.
was there a tag with the last C&S date?
were you able to inspect the flue and chimney?
just some thoughts,
CJ
It is hard to say what is causing this but even electric baseboard heaters have discoloration above them after a while. Does the discoloration rub off like it might be soot or dirt? Or does it stay the same like it is the paint aging?
Air filter not in place.
Noticing the silicone on the faceplate of the exchanger would indicate that a heat exchanger replacement or faceplate replacement had occurred in the past.
Staining around S/A Registers or R/A Grilles usually indicate an airflow problem. Usually low velocity (CFM) typically do to dirty filter(s). Low flow usually will cause a certain level of moisture/condensation causing bypass dirt, dust, etc. to cling to the register/grille or drywall, etc. This is true for most all systems (ie:Gas, Ht.Pump, etc.). Filters are easy to forget, fairly cheap to maintain, and can cause more problems than one might think.
As stated by others, I’d be concerned about cracked firebox, maladjusted gas/oxygen ratio, etc. I’d attempt to verify the age, remove the flame cover to get a better look inside the firebox, check filter and compoents beyond the return-air compartment (dust, dirt on the blades of the blower, etc), describe what I find and report a need for service.
The cause could be the furnace. Most streaking around regsiters is from airborne dirt that is entrained pulled into the supply register airstream from room air. Do a word search on candle sooting and streaking. Also a couple of articles at Home Energy dot org about this subject.
Do they happen to burn candles?