Common HVAC Smells and Their Causes

Smell is one of the key clues that something is wrong with your HVAC system. One small problem can cause unpleasant odors to be circulated through the vents and into your home. It’s important to know what these smells mean so you can have the problem repaired as soon as possible. Here are some of the most common HVAC smells you might encounter and what they mean.

Mildew or Mold

Moldy or mildew smells are probably the most common with HVAC systems. Condensation usually forms on some parts of your HVAC system, and it needs to be properly drained. If there’s an issue with drainage, the condensation can build up and cause mold or mildew to form. This may not be as serious as other HVAC problems, but mold and mildew buildup can cause or worsen respiratory issues for anyone in the home. An HVAC technician can easily find the source and fix the problem before it gets worse.


It’s common to smell burning gas when you first turn your heater on. Dust settles on the heat exchanger when it isn’t used during the summer, and turning the heater on causes it to be burned off. If the smell isn’t coming from the vents, it could be a more serious problem like a leaking pipe. Be sure to call an HVAC technician right away and don’t attempt to fix the issue on your own. 

Rotten Egg Smell

Utility providers usually add a sulfur or rotten egg smell to natural gas, which is usually odorless, to help residents identify leaks. If a harsh rotten egg smell is coming from your vents, it’s most likely a natural gas leak. You should immediately open the windows and get out of the house if this happens, and call your gas company right away.


If you smell oil, you should first look for a leak. The oil smell could be caused by a pipe or fitting that needs to be tightened by an HVAC technician. If it isn’t a leak, the problem is most likely the oil burner. Oil burner malfunctions can be caused by a range of issues, so watch out for smoke and unusual sounds. Call an HVAC technician to take care of the issue right away. 

Burning or Electrical Smell

It’s common for a burning or electrical smell to come from your vents when you turn the heater on for the first time. If the smell is too strong or lasts longer than a day, it could mean your unit is overheating. Turn it off and call an HVAC professional, but don’t try to find or solve the problem yourself.

Quality HVAC Repairs with Ellis AC

Regular HVAC maintenance is the key to avoiding serious damage and expensive repairs. Ellis AC offers inspections, maintenance, and repairs to keep your HVAC in great condition for as long as possible. We work fast to identify and treat the problem, and our team is always willing to answer any questions you may have. Call or visit our website for a free quote!

Scroll to Top