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exhaust smell???

I have an oil fired furnace with a power vent unit. when the furnace is running I get a slight smell of what I believe to be exhaust fumes. The system is about 10 years old, I started smelling it about 2 years ago, last year the system was fully serviced professionally and they found no problems. Everything seems to work fine, the power vent works fine, no excess smoke, I added extra co detectors around the house and have had no alarms. any ideas what this could be if it isn't exhaust? The only thing different is my oil tank was moved into the basement so I switched from kerosene to #2 oil about 3 years ago. thanks for any input.


  • Jamie HallJamie Hall Member Posts: 12,866
    When the unit was serviced I assume that the adjustments were made with the proper test instruments? I hope? Since kerosene and #2 require different settings...

    However. Check all of your venting ducting -- particularly exhaust, but intake as well. Make sure it is firmly put together and that it isn't obstructed anywhere, inside or out.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • STEVEusaPASTEVEusaPA Member Posts: 4,144
    How much post purge on the power venter? Is it a power venter that is on the exterior wall pulling all combustion gases through the flue pipes (everything negative in the flue) or one pushing combustion gases (everything positive in the flue and needs/missing some sealant).

    Where do you smell the exhaust?

    I'd double check all the following on the tank first:
    -Any leaks around the tank-(stains on the fill or vent, cracked/loose plastic on the tank gauge), or any residue on the oil line or filter?
    -Go around with a white paper towel and look for red stains-from the tank to the oil line/filters, to the unit.
    -Doesn't take much oil to make a smell. Could be a few drops from the pump into the blower compartment. Could even be an oily rag somewhere in the basement.
    -Are the fill and vent pipes sealed in the walls so exhaust fumes aren't migrating back through some gaps and being pulled into the blower from negative pressure created by the blower motor and the power venter.

    If you only smell it when the unit is running, all the above as @Jamie Hall mentioned, but also you have to consider make up air requirements. Look for loose/missing caulk/sealant where the power venter exits.
    Check doors/windows in the exhaust zone to see if it's not migrating back into the house.
    I'll assume the power venter was installed with proper clearances above, below, next to, windows, doors, etc.

    More things to consider:
    -It's possible that when your furnace was cleaned, someone didn't re-install the cleanout gaskets properly, or they didn't replace failing gaskets (or tighten them).
    -And it's also possible that your heat exchanger is cracked.

  • EdTheHeaterManEdTheHeaterMan Member Posts: 579
    Kerosene burns cleaner than #2 oil. Is the odor inside your home or outside? The change from #1 kerosene to #2 heating oil may have something to do with the change in the smell.

    There will always be an odor to the fuel exhaust. Less with kerosene, more with #2 fuel. If you are smelling it outside, then don't go there! (reminds me of the man who went to the doctor and said "Doc, I broke my leg in 2 places." The Doc said "don't go to those places anymore!")
    Homes with regular or manufactured chimneys have the exhaust leave the building well above your head, so the odor is rarely detectable. When you have a power vent out the side wall, the odor is closer to the ground, easier to smell.
  • EdTheHeaterManEdTheHeaterMan Member Posts: 579
    Follow up
    If you are smelling the odor inside then never mind what I just said.

    You need to determine if the odor is raw fuel smells like diesel fuel or exhaust that smells like you are stopped behind a bus at a traffic light

    Exhaust fumes inside are more hazardous because they can contain carbon monoxide.
    Raw fuel odors inside the home are just annoying.

    Determine the type of odor and that will send you in the direction you need to look

    Raw fuel = Tank leaks and or fuel line leaks.

    Exhaust fumes = cracked heat exchanger, or failed gaskets on clean-out ports or improper pre purge or post purge timing, or vent pipe problems.
  • dwilliamsx6dwilliamsx6 Member Posts: 2
    Thanks for the input, I am a mechanic by trade so I know the difference between fuel and exhaust smells, the smell is exhaust and it is being blown all over through the ductwork. The powervent is at the wall so it is a suction type, it turns on, then the vacuum switch allows the furnace to fire and it continues to run for approx 30 secs after burner shuts down. the seal at the wall is intact and there are no other penetrations near it on that wall. the vent pipe to the unit is in great shape and is sealed well. since the smell was present before the service I would hope they would have noticed bad gaskets, it was an established company with a great reputation. they also left a card with efficiency numbers and other info that would appear to have needed proper instrumentation to obtain. since none of the obvious stuff seems bad I am leaning to a cracked heat exchanger, does this sound right? I am still curious as to why no one is affected by this, shouldnt we be getting sick or having headaches or something and why havent any of my four CO detectors picked anything up? I was thinking of calling the local fire dept to see if they have a fancy CO detector and if they would test for me. at work I have a scope with a camera on it, if I pull some inspection panels what or where should I look for? will the cracks be obvious? its a Newmac brand lowboy with a ceramic looking material combustion chamber. thanks again for the help.
  • STEVEusaPASTEVEusaPA Member Posts: 4,144
    First try changing the post purge to 3 minutes, not 30 seconds. Should be even longer with a power venter, like 5 or 8 minutes.

    Also, from my previous post...

    More things to consider:
    -It's possible that when your furnace was cleaned, someone didn't re-install the cleanout gaskets properly, or they didn't replace failing gaskets (or tighten them).
    -And it's also possible that your heat exchanger is cracked.


    You should get a competent tech over there who knows how to look around for the above mentioned things, and knows how to use an analyzer. They should go over the burner, even pull the burner, check the chamber, check all the gaskets, check the end cone, check the flue pipe, z-dimension, pump pressure, proper nozzle and air band settings. Then full combustion test-draft, smoke analysis.
    As the blower motor overpowers the burner motor, you should really never smell flue gas in your duct work. But your analyzer could detect a change in combustion with the fan on vs. the fan off
    If you call the fire dept., and they detect any CO (regardless of the source), they will most likely shut down/red tag your unit and you'll have to get a professional in there to prove it's operating safely. a guy, or gal.
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