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  1. #1

    7 Months of smells

    Hi All,

    I bought my first home 7 months ago, and we've been having issues with strange odors in the house ever since. It's hard to describe , it's a musty type of dead smell, but I can't tell if it's sewer gas, or some type of odor from the furnace, either way we just can't seem to find the source. We have an Oil furnace/AC system in the basement, which is about 15 years old. Each room on the 1st and second floor have it's own return and supply vents, about 32 vents in all.

    When the heat, AC, or fan is is on, we don't really get an odor, but when it turns off, that's when we start to notice it. It seems like the system will kick off, and a then we'll get a very foul odor in only 2 specific rooms in the house( on total opposite sides of the house) the smell only comes from the return vents in these two rooms, all other returns and supply vents do not smell at all.

    Strangely, we also notice the smell coming from the return vents in these two rooms when they system is turned off completely. We've had renovations going on for the past 3 weeks now, so the system has been shut off completely, yet we are getting a strong odor from the return vents. The whole system including the fan is off, but some how it really smells from these vents , and seems more of a sewery dead type of smell.

    We've been trying to investigate what it is and here's a list of what we've done so far.

    - Oil company service and tested the furnace ( cleaned out some stuff and tested the plugs). This was in October, we have them scheduled to come out in June and fully clean and test the system.
    - Mold specialist came and inspected ducts/vents with camera
    -had ducts professionally cleaned by a company with hundreds of positive reviews on angieslist
    -had plumber come and inspect pipes, cleaned lines, and flushed p traps. I however was not very impressed with this guy, and I unfortunately wasn't home when he was here when he came back a second and 3rd time to test everything. My wife said he went into the attic to inspect the vent pipes but not sure if he actually did anything.
    -had pest control come in an check traps, inspect for openings, no rodents in ducts, and it's been a problem off and on for 7 months, so a rodent would have decayed by now.

    So at this point , we really have no clue who to call next.

    Is it possible that the furnace exhaust vent that goes to the outside could be an issue? If it was cracked or not sealed properly would that somehow leak a smell in the return side and travel to these vents?

    One similarity is that although the rooms with the problem vents are across the home from each other , they both seem to be on the same return line. We have a bathroom on the second floor which seems to be very old, and i do notice some weird smells here or there but they are no way as bad as the smell from the vents, and I'm not sure they are the same smell. The bathtub seems to be partially clogged or slow to drain, and that pipe seems to be
    very old in the basement. That pipe does come near that return line, and the actual pipe does seem to smell a little, but again not really the same smell im noticing from the ducts.

    I'm really not sure at this point who to contact about the issue, another plumber, another HVAC guy? Do you guys have advice?

    Really appreciate any help or advice.



  2. #2
    This may be more suitable for general discussion..please move if necessary - thanks!

  3. #3
    Join Date
    May 2013
    I would be concerned about a cracked heat exchanger. Id call a tech to come out and check the furnace sooner than later.
    With it being 15 years old its a good possibility. As your furnace turns on and off (hot then cold) the heat exchanger expands and contracts and cracks will happen over time.
    It will give off a nasty formaldehyde type smell.
    Are you or anybody in your house getting headaches more than before? Do you have a carbon monoxide detector in the house?
    Definitely get the air quality in your home tested as the combustion gases that can leak from a cracked heat exchanger are dangerous.

    Sent from my SGH-I337M using Tapatalk

  4. #4
    Thanks for the reply, I will have that check out, I have my oil company scheduled in June for a full maintenance. Now that we are in the warmer months we won't be using the heating side of the furnace at all, is it still possibly harmful at this point, and if it's not using oil would we still get the affects of it?

    We haven't had any headaches really . We have a carbon monoxide detector hard lined in the basement about 10 feet from the furnace, one coming up the stairs of the basement, 2 on the main level, and 2 on the 2nd floor, so I think that should cover it

  5. #5
    Join Date
    May 2013
    No as long as you dont turn on the furnace there is no risk of carbon monoxide. But definitely wait until it is inspected by a professional before you turn it on again.

    Sent from my SGH-I337M using Tapatalk

  6. #6
    Join Date
    May 2014
    Bay Area California
    Quote Originally Posted by JRoz View Post
    Hi All,

    I bought my first home 7 months ago, and we've been having issues with strange odors in the house ever since. It's hard to describe , it's a musty type of dead smell, but I can't tell if it's sewer gas, or some type of odor from the furnace, either way we just can't seem to find the source. Jason
    In my experience, the vast majority of odors come from one of two places. The first place is the evaporator, or indoor coil for the A/C. Or the condensate pan that catches the condensate run off. Seeing as how you've been going through what you have, you may want to consider removing that coil and having it pressure cleaned. Dust and other filth can collect between the fins and it will not be noticable by just looking at it. Then moisture hangs on that filth; an excellent breading ground. Just be careful that the fins don't get all bent over with too high of pressure at the wrong angle.

    The second most common source (again, in my experience) is the fresh air make up. On small residential systems, there usually isn't one. But it sounds like your system is big enough that there may be one. If there is a fresh air make up, where is it located? Where is it located relative to the sewage vents for the indoor plumbing? Or any other source of smells, like a cat or dogs favorite pooping spot? Which direction is the prevailing winds? Keep in mind that as air flows over a building a vacuum can develop on the down wind side, sucking fumes from an exhaust vent and pushing them down to or near ground level.

    I once had a similar problem in a laboratory. They were complaining of sewer smells. I checked all the basic stuff, then had an idea. I went back to the shop and got the flammable gas detector. Went in the lab and immediately traced the odor to a floor drain that had been covered up by a floor mat. The trap in the drain had dried out. So we poured vegetable oil down the drain to keep the trap full (the oil wouldn't evaporate like the water did).

    That's just a though for you. In my case, the flammable gas detector did detect sewer gasses. If you try it, be sure to calibrate it outside in fresh air before going into the house.

    Here's another thought that won't cost you a dime. Go on the roof with a garden hose. Put water down every vent pipe. Just be safe about it, you know, don't forget about the dangers of heights and sloped roofs. Maybe there was a remodel at some point and there is an abandoned trap that dried out.

  7. #7
    Join Date
    Jun 2003
    Madison, WI/Cape Coral, FL
    This an experience from my uncles house. Hous stunk, uncle died. In the following remodel, they found a rotted sewer vent in a wall. Fixed and the end of the problem.
    Fresh air ventilation is also suggested.
    Maintain <50%RH throughout. Keep us posted.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  8. #8
    Join Date
    Aug 2009
    Prattville, Alabama
    We had a problem with the clothes washer drain overflowing. It turned out to be a blocked plumbing vent. I thought of this when the OP mentioned one of the bathtubs was slow to drain.

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