There is a burning smell that wafts out of the vents of my 15-year old, 3-level townhouse (top level is a full unfinished attic with no HVAC).
The bottom level of the townhouse is the main level (with the front entrance door) and sits on concrete slab. The burning smell occurs in all weather, all seasons of the year, with the HVAC unit on or off, HVAC fan on or off. The cause of the smell is not electrical, 3 master electricians ruled that out. It is not the HVAC fan, that was replaced and there was no improvement.
This burning smell has been happening, year round, for over 5 years. It was pointed out to me that one of the HVAC pipes on my roof top is 1/3 the height of all my neighbor's (see the pictures). I have gas heat.
I think this pipe on the roof is related to the gas furnace. If the pipe on my roof is too short, and it is connected to the gas furnace, could that cause a backup of the gas pilot light/fumes to flow back into the HVAC unit to then exit through the ceiling vents into the two floors of the townhouse?
The burning smell is so bad at times that I have to leave the house or put box fans in the windows to clear the air.
Additional details originally posted as an answer:
First, thank you to everyone who responded to my post!! Your time and response is very much appreciated. Below is response to the responses we received.
We rent and our landlord advised that for the first 7 years he lived here they never had a problem with this smell. Actually, the problem began 2 years after we moved in and has continued for 5 years.
We just heard back from the landlord and he does not believe the short height on the stack pipe on the roof could be the problem. At this point, we are willing to try in hopes it may help. But landlord approval is required.
Regarding neighbors - have talked with both, they never smell it. We have had the smell occur when the neighbors were away on travel. Don't think they are the cause.
We are not the only ones who have smelled the smell in our townhouse, so it is not imagined. The very first time I smelled it, I thought it was an electrical burn.
The smell is intermittent. It starts and builds over a period of 3-4 days with the smell intensifying till it is maddening, then it abruptly stops and we have 2-3 days of relief, then the process starts over. We have taped coverings over ceiling vents in the bedrooms to keep the smell out - just closing the vents was not enough. The smell still got through, although diminished.
I can distinguish between the smell of metal, plastics, animals, mold, chemicals, and decomposition. The smell is not like the pilot light in our fireplace or the smell when using the stove or oven. It is most closely associated with the smell of an overheating electrical unit or electrical burn.
We have literally turned off circuit breakers in sections of the house for days, thinking the smell may be electrical in nature, but that didn't stop the smell.
We are truly baffled by what is producing the smell and why it is coming FROM the vents. After 5 years of doing every process of elimination we could think of, and that others suggested, I am now convinced the smell is originating within the HVAC unit.
The gas water heater sits beside the HVAC unit in the laundry room on the middle floor. There are no smells coming from that unit, it has been checked frequently.
All of this (and more) is why the has been referred to as a MYSTERY.
We have made two discoveries as we have tried to deal with clearning the air - if we run the exhaust fans, they cause the smell coming out of the ceiling vents to increase. If we place the box fans in the windows and blow air into the house, that will cause the smell coming out of the ceiling vents to decrease. Someone told us using the box fans in this way creates a positive pressure in the house and that is why it helps.
I don't know if this additional information helps in further solving the mystery, but I hope so. We are still open to any further thoughts, recommendations, thoughts, feedback you may have.