HVAC units are odor neutral. This means they supply cool air or provide warmth minus any type of odor. Smelling something emanating from the HVAC unit can definitely signify something about its operations.
The San Diego HVAC Contractors’ Association (SDHCA) says odors emitted by a home’s HVAC unit clue in owners about a possible concern in their air conditioning and heating system. The SDHCA says anything that smells like gas, or burning should warrant an automatic shut off, and an urgent call to the homeowner’s trusted HVAC technician.
Homeguides SF Gate has published an article decoding what foul odors coming from the HVAC may mean. One of the type of smell that they discussed is the dirty socks type of odor.
“The odor comes from the mold that has made a home on your unit’s evaporator coils, on the surface of the liner, in the drip pans and on drain lines, according to the Florida Department of Health. The odor is one indicator of the mold; it’s an earthy, stale, musty smell that actually does resemble a dirty sock odor. You can smell it coming from the ventilation system, but the culprit is a slimy, dark sludge that feeds on the moisture in the high efficiency unit.”
Read more here.
Sewer-like Smell
A sewer like smell can also emanate from the HVAC unit, and experts explained that it may not necessarily come from the system itself.
“Air conditioning equipment itself would not produce a septic odor but the system might pick up and redistribute an odor or gas from somewhere else, or in certain conditions negative air pressure in a room might cause sewer gas to backdraft out of a drain system. Air conditioning refrigerants are odorless. Air Ducts Draw In Gases: We have found instances of drain pipe leaks or plumbing vent leaks that happened to be near an air intake return register at central heating or central air conditioning systems.”
The rest of the explanation can be found here.
Burning Odor
Third-Party Service Ratings Website Angie’s List shared as well a similar article decoding possible meanings of HVAC odors. In their write up they mentioned that burning smells warrant the immediate attention of an HVAC Technician.
“If you notice an odd burn smell when the heat turns on, it may be a sign that your furnace needs maintenance. It could be something as minor as a dirty filter, but it could also be a serious problem like a broken electrical component in the furnace. Don’t ignore it. Try to find the source of the odor to avoid costly repairs in the future. You should not ignore a foul burn smell. Try to find the source of the odor to avoid costly repairs in the future.”
The original web post can be found here.
The SDHCA Advises homeowners to never ignore smells coming from the HVAC unit. According to the contractors’ group, HVAC should never emit any type of detectable odor, and its emanating of such can mean issues within the system.
Reliable Standard Heating and Air Conditioning Service
AC Repair Contractors Association San Diego 