Unusual HVAC Smells and What They Mean

It’s that time you turn on the heat or air-conditioning on again after a period of nonuse. But do you smell that? It smells like…dirty socks or rotten eggs. When you first turn your HVAC on in the spring, there’s always a unique smell. Knowing what the HVAC smells mean and getting them fixed can help you prevent more serious issues later down the line.

Rotten Eggs

A rotten egg smell coming from the HVAC system could be a natural gas leak. Natural gas is odorless but often mixed with other chemicals that give off an odor. If you smell rotten eggs, call your gas company immediately and report the smell.
Also, if you smell this odor, don’t assume it’s safe to turn on the lights or use electrical appliances. Natural gas can cause fires and explosions. Leave your home immediately until a technician locates and fixes the leak. Booking regular HVAC maintenance will help prevent any gas leaks from your HVAC system.


The main cause of sewer gas in a house is a clog in the sewage line, but you could also have a problem with the sewer venting system or drainpipe. When you notice a sewer gas smell, it’s important to find out what’s causing it so you can repair and eliminate the odor.
Here are some common causes of sewer gas smells inside your home:
  • Clogged pipes – Your pipes may be clogged, leading to a build-up of sewer gasses that enter your home through drains or vents. This can happen over time if you don’t have regular plumbing maintenance done on your system. You should check all drains and toilets regularly for signs of clogs and use drain-clearing products as needed to clear out debris.
  • Fractured sewer line – if your HVAC system is close to a sewer line, any leaking sewerage will seep near your system. The smells will then filter through your vents.
  • Dirty filters – air filters collect pollutants from the air. If they become clogged, they can start to emit nasty odors.
Always contact a professional plumber and HVAC technician to deal with sewer smells. Methane can be dangerous to your health.

Dirty Socks

If you’ve ever opened the door to your home to find that it reeks of dirty socks and stale air, you’ll want to get rid of it quickly. Dirty sock smells are often caused by mold and mildew on the evaporator coil — the part of your HVAC unit that cools the air before it’s circulated throughout your home.
If you see mold growth on a coil or evaporator, get an HVAC technician to come out. Mold can be hazardous and potentially cause serious health problems such as asthma attacks and allergic reactions if inhaled.
Booking regular HVAC tune-ups throughout the year helps prevent smells and keep your HVAC system clean and in good working order.


If the air from your HVAC system smells musty, you will likely have a problem with mold in your ductwork. This can be a serious problem for your health and the life expectancy of your system.
Mold is typically found in moist environments and thrives on cellulose materials like wood, paper, or dust. If this happens inside an HVAC system, the air will start smelling musty and eventually become unhealthy to breathe.
The best way to prevent this from happening is by preventing mold from growing in the first place. To do so, you need to make sure that your system and ductwork are adequately cleaned. The easiest way to banish unpleasant HVAC smells is by booking regular HVAC tune-ups with a professional HVAC technician.

Electrical Odors

Electrical odors can be caused by the HVAC system itself, but they can also be caused by something else. If you notice an electrical odor coming from your HVAC system, it’s important to find the source. An electrical smell could lead to a fire or other safety hazard.
If you smell burning rubber or plastic while operating your air conditioner, this may indicate that the motor has overheated. Overheating motors can cause damage to other parts of your unit and cause carbon monoxide to leak into your home.
Check the capacitor on top of your blower motor for signs of corrosion or cracks that might require replacement. A bad capacitor can cause short circuits inside your unit, leading to overheating.


The most common reason for the oil smell in your HVAC system is an issue with the compressor. When compressors run, they produce oil that is used to lubricate and protect the internal parts of the compressor. If there is a compressor leak, you will notice an odor coming from your air ducts.
Struggling to find the source of your HVAC smells? Contact the HVAC experts at Moore Home Services and eliminate those odors.