Old furnace - bad air flow

[njguy99]

I've been hunting around the forums for a bit now, but couldn't find an answer to this question, so I figured I'd post. Any advice would be much appreciated...

I have a 20+ year old Trane forced-air gas furnace - about 45000 btus. I live in a small condo, only about 700 square feet. We have 6 output registers and 1 intake for the unit.

It runs well, but the air output is very low. Some days, the only room that gets warm is the utility room where the furnace is located.

I've had yearly checkups, and all the techs tell me everything is OK but my furnace blower is "undersized" and I should replace the unit. I popped open the service panel today - the first cold day in a while - and noticed a white residue all over the plate below the pilot light. I also notice that, when the fan kicks on, it's blowing a lot of air out the top of the furnace - near the flue, but not into the vent. (A flag held over the top-front of the machine whips like a US Flag would on a windy day).

[I never noticed either of these symptoms before...]

What do you think? With so many different answers, I don't know who to trust. Should I be worried about air being blown through the top of the machine? What about the white residue?

I'm kinda worried that this might be the first sign of my heat exchanger going south.

Any ideas?

[aircooled53]

Sounds like air leaks, maybe combustion not good if white powder is on the burners..

Best Idea: call another company and have them check evaporator coil,heat exchanger , gas mixture, combustion air and blower....

[docholiday]

Could be a fire damper slammed shut (if there are any).

[njguy99]

Originally posted by docholiday
Could be a fire damper slammed shut (if there are any).

Thanks Doc - but the system doesn't have any dampers. The more I look at it, the more it seems like air is escaping from below the flue and traveling right out the top of the furnace.

The air velocity there seems to be greater than it is coming out of my registers. Is that indicative of anything other than just leakage?

[BaldLoonie]

Plugged A coil would be the first place a tech should look.

[jeffshvac]

absolutely check the coil if its also 20 yrs old.ive seen newer coils get clogged up.

[njguy99]

Originally posted by jeffshvac
absolutely check the coil if its also 20 yrs old.ive seen newer coils get clogged up.

Thanks guys. I'm having someone come take a look at the machine today - so I'm gonna ask him about the coils.

One question: is it easy to clean them? Mine are behind the ductwork, so I imagine they'd have to cut an access panel in order to even inspect them.

[njguy99]

Well...you guys were right. They cut the ductwork open, and, in the words of the tech who was looking at it, the coil was "filthy." Even to my naked eye it looked dirty - covered with muck and grime, the bottom of the coil was starting to rust. A mess. He cleaned it, but there's only so much you can do with a 20-year-old system. We're probably going to replace it within the next few weeks.

Thanks everyone for your help!