April 21st, 2021

Cosmo here! As you may have heard, we dogs have an incredibly sensitive sense of smell. That’s a good thing when we smell a tasty treat being cooked up, but not so great when we smell something bad – like strange, foul odors from a furnace, heat pump, or water heater! Here are some unusual, bad smells you might notice coming from your home’s HVAC system and what might be causing them.

Electrical Odors from HVAC System

An overheating HVAC unit will produce an odor reminiscent of chlorine, if you can imagine burnt chlorine. But what causes overheating in the first place? One possibility is air restriction caused by dirty air filters.  If this is not the case, it’s could be a motor or wiring issue, something you should call a professional technician to address. 

Dirty Sock Syndrome

Despite the name, this is not a foot condition. In fact, it doesn’t actually have anything to do with dirty socks. It refers to a moldy or mildew smell coming from your HVAC system, an issue that commonly happens to air conditioners in the spring and to heat pumps in the fall, when these systems kick on and turn off most often. The smell comes from the accumulation of dirt, dust, and moisture, as well as mold and mildew, on the system’s evaporator coil while the system is not in use. When the system turns on, these substances and organic materials blow into the home and create the odor. 

Furnaces and heat pumps can both experience Dirty Sock Syndrome, but for different reasons. Heat pumps are more susceptible to the presence of mold and mildew because the devices don’t reach temperatures high enough to kill these organisms. Furnaces, on the other hand, can reach temperatures that are high enough to kill most mold and mildew, but also burn off dust accumulation in the process. This can produce a weird gassy smell when the furnace first turns on. If the smell occurs right at the start of heating season the first time the heater kicks on, there is no immediate cause for alarm; the strange smell should go away within a half-hour or so. However, if the smell persists after that, there is a problem, and the solution is to have a professional technician check and clean or service your furnace or heat pump. This will identify the source of the foul smell, and improve your home’s indoor air quality of your Princeton, NJ home to boot.   

HVAC System or Water Heater Smells of Rotten Eggs

If your boiler or water heater smells like rotten eggs, this unusual odor may be an indication of the presence of anaerobic bacteria. These organisms grow on metals like magnesium and aluminum, which are contained in some boiler components and thrive in dark, moist environments. If anaerobic bacteria is the cause, it’s time to clean or replace the parts where the bacteria has grown.

If you don’t have any actual rotten eggs in your home, and bacteria isn’t the issue, another possible source of a rotten egg smell is a natural gas leak. A common culprit, hydrogen sulfide, is the same gas given off by rotten eggs. A gas leak can be serious, even deadly, so get out of the house and call 9-1-1 or your gas company immediately.

For more information, watch this video from our friends at Northeast Gas Association:


Smells are subjective, but that doesn’t mean you can’t trust your nose. If your nose is telling you something is wrong, don’t ignore it. It could be a sign that your furnace needs repair. In the Mercer County, NJ area, the company to call for quality HVAC repairs is SG Heating & Air Conditioning LLC. Our number is 609-448-1273, and we’re looking forward to making your house smell like home again!

Now I know a lot more about the strange smells we should all be wary of. I guess sometimes being “Nosey” is a good thing! Woof!

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