Covering up an odor with an air freshener.

The smell of freshly cut grass, apple pie baking in the oven, a pot of freshly-brewed coffee…these are just some of what many consider to be pleasing scents. Then there are those smells that assault your nose and make your eyes water, like spoiled milk and last week’s leftovers. If you’re lucky, you can find the cause and banish the stench, quickly. No harm done.

But what about those mystery odors that you can’t quite pinpoint? They could be a sign that trouble is brewing with your HVAC system. Read on to learn which odors you should never ignore.

Rotten Eggs or Sulfur

Because natural gas is odorless, a chemical is added to it to make it detectable in the event of a leak. If you notice a rotten egg or sulfur smell in your home, do not use any appliances or electronics and evacuate the house immediately. Call your gas company from a safe location and do not re-enter your home unless you are told it is safe to do so.

Stinky Feet

Do you smell stinky feet whenever you turn your HVAC system on? You may have undrained water sitting stagnant somewhere in your HVAC unit. Stagnant water can attract fungi and mold, which can be dangerous to your health, particularly if you have allergies, asthma, or other respiratory issues.


It’s hard to ignore the smell of sewage. Coming from your plumbing, it can mean there is a crack or leak in the sewer line. But what if you notice it whenever you turn the HVAC system on? If a sewer line is located near your ductwork, it may have ruptured and leaked, sending methane gas into the HVAC system. This is a plumbing and HVAC emergency as methane gas can be harmful if inhaled in large quantities.

Burnt Smell

As you fire up your furnace for the first time of the heating season, you may notice a burning smell. This is quite common and not a cause for concern. As your heating system sat dormant all summer, it collected layers of dust on the heat exchanger and in the vents and registers. When the heating system is first turned on, the dust gets burnt off. The smell should go away in a day or two.

If, however, you smell a burnt smell coming from the AC unit and not from the vents, there’s a good chance that you either have a leak at a pipe fitting somewhere or a leak within the equipment. Contact an HVAC professional right away.

Musty or Moldy Smells

It’s not unusual to smell mold or something musty whenever you turn on the HVAC system. HVAC systems can collect a lot of condensation within the units and if not drained properly, this condensation escapes into the ducts and creates the perfect environment for bacteria and mold to grow. However, if ignored it will negatively impact your home’s air quality and exacerbate respiratory issues.

Pinpoint the Problem

If you notice any offending odors coming from the HVAC system, contact Zach Heating & Cooling right away. After providing us with some details as to what you smell, when and where you smell it, and whether it’s accompanied by any sounds, we can tell you whether it signifies an emergency or simply a problem that should be dealt with sooner rather than later.