We have a carrier gas furnace. Starting about 2 months ago, VERY occasionally vents on one side of the house start emitting a very strong odor that I would describe as a smokey rubber odor. The smell happens at all times of the day, is expelled from the vents for about an hour, and within and hour or two it is gone. It seems very clearly to come from vents in one part of the house, and if you walk by the heater when it is coming out from the vents the heater does smell.

We have had the heater checked out, and he could find nothing wrong. The gas company has checked for gas and CO, and they found nothing. We've had the vents cleaned, and it still happens.

HELP!

Thanks.

It sounds as if maybe something fell down in the ducts on that side of the house? And the heater itself is warming it to a melting smell? Interesting thought.

Duct temperature should only get up to about 140 degrees F. Not hot enough to heat up rubber and make it smell. Something would almost have to be laying on the heat exchanger, which I have seen before. I would look at the evaporator coil, drain pan and blower motor for possible causes.

Sometimes a home owner needs to do their own detective work. Northern Heat is right, the only part of the furnace that should be hot enough to produce burned rubber is the heat exchanger, and for the smell to get into the vents, it would have to be on the inside. I think it would then spread to all the vents. If it is always the same vents, poke around them. Look for some other source of heat, a quartz light or something, that could heat up the duct and burn off the collected crud. Could something that doesn't need to get that hot be getting spilled into the vents? The guy that checked the furnace might have missed something like that, but he should have spotted any problem like a leaking heat exchanger.

If and when you find the problem, post back and let us know.

By the way how old is the furnace and what is the efficiency. I know several US states are in litigation over the 90+ Carrier furnaces and Carrier is unwilling to do anything about it. I live in Indiana and we are'nt in the suit yet but Michigan is, and I believe Texas won't let them do business in that state until something is done about it. The problem is in the secondary heat exchanger and the suit is for using inferior materials.

I happened to be in the basement yesterday for the start of one of the "incidents." Here is the chronology:

Our heater (a Carrier combination gas furnace/A/C) is about 17 years old. When the heat kicks on, it goes in phases. There is a minute or so cycle where it sounds like there is a small fan kicking on and the pilot light and burners are starting to heat up. After about a minute, the blower starts.

Last night, I heard the sound of an electrical circuit turning on, and after about 20 seconds it turned off. The blower never kicked on, and it sounded like the “startup” phase didn't finish. A few other things I noticed - we have a humidifier that turns on ONLY when the heater is on. After that circuit/pilot sound, the humidifier started to run and didn't turn off although the blower never started. (coincidentally or not, the carpet near the heater was soaking wet. I think that the humidifier was running when these things keep happening, and overflowed onto the carpet. But that's just my theory.)

I went up to the thermostat, a digital Honeywell connected to the power from the heater. The thermostat was blank - the time and temperature was off. I tried to turn the switch from auto to "on" to manually switch on the heater, and there was no response (We'd typically hear the sound of the heater's initial cycle turning on).

I went upstairs, AND THE SMELL (like metallic burning rubber for those new to this….) HAD STARTED. It was very strong.

I went down to the basement to see if the heater was smoking or anything, and it wasn't. The smell wasn't particularly noticeable next to the heater. I was down there for about 5 minutes, and went back to the thermostat, which had switched back on. I played around with the temperature and fan (which went on). Initially, the system was only blowing air that wasn't being heated. After a period of about 20 minutes, I was able to get the heater to start blowing hot air. The odor coming from the vents had traces of the smell for about an hour, and then the smell had mostly gone away.

It apparently happened again this morning – my wife called and told me she detected the odor again.

Does the new information help? Between the increasing frequency (at least once a day, where it used to be every week or so) and the quirkiness with the humidifier and the blank thermostat, this seems less like a duct problem and more like an electrical problem to me. We did just have the ducts cleaned, too. I'd hope that the cleaning would have gotten out any dead animals in the ducts. But I know nothing…. 

I would open up the furnace and take a good look at all the wiring in it. It sounds like something is burning in there, and there isn't much else it could be. Smells are hard to describe, but your description of metallic could be from burning vinyl electrical insulation. It is different from the sulfur in rubber or the phenolic found in over heated motors. If you find a problem, you may still need a pro. It isn't enough to replace failed components, you need to look at why they failed.

Some times you have to let a problem get worse before you can find it.

I have American Home Shield, so we have a tech there today. It only costs $55 including labor and parts to fix anything. I'll report back in case people are curious and/or he says something that doesn't make sense.

I did a service call with the same problem. After checking the system I found out it was a dvd player going bad the smell was being pulled into the return air and then out the supply ducts. Good luck.

When I worked in a paint factory, everybody would absolutely panic when the neighbors would burn trash across the alley from our ventilation intake and fill the building with the smell of burning paper.

My best guess is that the blower motor is losing oil , its over heating and stalling on an internal overload,. the smell is oil from an overheated motor

Update and answer for anyone interested -
It appears to finally be fixed. Apparently the "capacitor" that was supposed to jumpstart the blower was faulty. It didn't charge up enough, so sometimes the blower never started. The odor was caused by the burners firing up and frying all the dust on the elements, which burned because of the lack of airflow.

I have the same issue coming from this one section of my home. This thread has been very helpful and I hope to try the same thing on mine. If anyone has any other suggestions, please advise

jonandabby, I have the exact problem described in your post. What was the resolution?

Replace blower motor run capacitor.