AirAdvice explains some of the more interesting sources of that mystery smell when it comes to indoor air quality.

The support team at AirAdvice fields calls from HVAC contractors across North America on topics ranging from basic indoor air quality to advanced home comfort. The more difficult questions usually go something like this, “My customer has a funny smell in their home and they want us to figure out where it’s coming from.  Where do I start?”  They decided to pool their collective expertise and talk about a few of the more interesting sources of that mystery smell.

Musty or Dank – Excess moisture in the home can cause mold or mildew to form everywhere from your air conditioner to your clothes hamper and creates a stale, musty odor. Keeping humidity levels below 55% can help with this. Also, exposed earth in a crawlspace or basement can also take on a musty odor.  Sealing the crawlspace with plastic and sealing or finishing the basement can get rid of the funk.

…Dead – We’ve heard about everything from birds decomposing in dryer vents to mice caught in the wall cavities of brand new homes. However they get in, decomposing animals smell terrible. Unfortunately, short of ripping out the wall, the only remedy is time.

Sewer – Sewer gas lives in your plumbing. Fortunately, we don’t have to smell it thanks to the “P Trap” on every drain in the house. That’s the U-shaped bend in the pipe leading away from the sink. This pipe normally has a little water in it all the time to prevent the sewer gas from drifting up into the home. But, if you never use the sink in the downstairs powder room, the water in the P-trap can evaporate, and the sewer gas is released. To prevent that foul sewer odor, run water in all sinks and pour a small amount of water into any floor drains once a month or so to keep the water in the trap from completely evaporating. Also check wax seals around any toilets. If the seal is damaged, the same sewer odor can occur.

Fishy – This is the one that seems to baffle homeowners most often. Where on Earth could that fishy smell be coming from?? Interestingly, it is usually coming from burnt wiring or something plastic touching a light bulb. Older wiring in particular has a fish odor associated with it when it melts or burns.  If you smell something fishy, check your outlets, light fixtures and other sources of wiring for overheating or damage.

Rotten Eggs – That sulfurous odor in your home could be coming from a couple of difference sources.  Sulfur is added to natural gas, which is naturally odorless, to alert people to a potential gas leak. If you smell rotten eggs in your home, the very first step is to call your gas company and have them confirm or rule out the presence of a gas leak. Breathing natural gas can be fatal. Once you’ve ruled that out, see if you can get closer to determining the location of the odor.  If it is coming from a faucet, then it is likely coming from something called an anode in your hot water heater or well. Check with your plumber for details, but it may be necessary to chlorinate the water in the tank or well.

Of course, this isn’t an exhaustive list.  But over time we have found that these are the most common culprits to the “What is that funny smell?” question. 

source: Air Advice Inc.