Keeping Your AC System Cleaner

3 Reasons Why The Cool Air From Your HVAC Smells Bad

by Yolanda White

If you smell a bad odor in your home that seems to get worse when your air conditioner kicks on, there could be a problem with your HVAC system. Depending on the cause of the odor, a service call for cleaning and repairs might be what's needed to solve the problem. Here are some things that can cause a bad odor to waft out of your air conditioner and how to fix them.


Mildew is common on HVAC systems. If you notice a musty, mildew odor it could be coming from the evaporator coils or a clogged condensation drain. Condensation naturally builds up on the parts of your air conditioner, but it normally drains away without causing any problems.

If something blocks the water so it accumulates or overflows, then mildew will grow inside the HVAC and give your home a musty odor. In addition, stagnant water has a foul smell of its own that contributes to the bad odor in your home. Another place mildew strikes is in the ducts. Mold can grow in your ducts also if it spreads in there from a wet attic.


If your ducts have rodents in them, the air blowing through the ducts can spread rodent odor throughout your house. The odor could be from urine, droppings, or the musky body oil they produce. You might even have a dead rodent in the ducts that gives off a horrible stench of decay when the AC kicks on. Your HVAC contractor can send a camera into your ducts for a visual inspection to look for rodents, mold, mildew, and other problems that cause your home to smell bad.

Stale Smoke

If your home was filled with smoke from a small kitchen fire, the odor may accumulate in your HVAC and ducts. Smoke damage can happen even when there is no fire damage. Also, if someone smokes in your home, the odor of stale cigarette smoke may cling to the internal parts of the AC so the air coming out smells like old smoke too. The solution is to have an AC repair contractor clean the HVAC. The only problem with this is that the odor will return if someone continues to smoke in your house.

Some odors are a nuisance and some could be a sign of impending problems. If your AC emits a burning plastic odor that you associate with an electrical fire, you should turn off the unit and call for repairs. Fortunately, many odors can be eliminated through cleaning and minor repairs. Still, it's best to have your HVAC inspected so the source of the odor can be identified to ensure there is nothing dangerous going on inside the air conditioner that could lead to the need for expensive repairs later.

Contact a service like GNL Heating and Cooling for more information.