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How to Diagnose Burning Smells Coming from HVAC Vents

by vscontent on September 29, 2017

Why is there a burning smell coming from my air conditioner/furnace (HVAC) vents?
Smell something burning? If it’s not your oven, stove, hair straightener, or iron, it may be coming from your HVAC vents.

There is a big difference, however, if the smell comes from your heating or cooling system.

Cooling System Burning Smell

If the burning smell is coming from your air conditioner:

A burning smell coming from the air conditioner is never a good sign. The cause is probably an overheating A/C fan or compressor. It may also be a circuit board or fan motor that has short circuited. If the burning smell gets stronger as you get closer to the air conditioner, turn it off immediately and call a professional HVAC professional right away!

WARNING: If, on the other hand, you smell a sulfuric, rotten egg-like smell, it could be a gas leak or burning electrical components. Since natural gas is naturally odorless, gas companies are required to add a chemical called mercaptan to the gas in order to alert people to its presence. The odor is often compared to garlic, skunk, rotten egg, or sulfur. This odor can also come from burning electrical components inside of outlets, switches, and other devices. Turn off power from the electrical panel and call an electrician ASAP. If you smell gas, immediately evacuate the household and call your gas company first, then your HVAC contractor.

Heating System Burning Smell

If the burning smell is coming from your furnace:

When you turn your heating system on for the first time, it is common to smell some burning. This is typically just the furnace burning off some dirt and dust accumulation.

If this is the case, don’t panic. It’s normal and the smell should dissipate after a few days. Still, this is one of the reasons why we highly recommend scheduling annual furnace maintenance in the fall before you first turn on the furnace or heating system.

When you schedule a heating tune-up, a qualified HVAC technician will inspect the entire system, including cleaning the area, inside and out. If you schedule professional annual maintenance before winter starts, you shouldn’t have any problems with burning smells coming from the furnace when you first turn it on.

If the smell does not go away or it’s not the first time you are using your heating system, there may be something else at play.

Similar to a burning smell coming from your cooling system, the cause can be an overheating fan or motor. If this is the case, turn the system off and wait until a professional HVAC technician has deemed it safe to turn back on. If you continue to use your heating system when there is a burning smell, the overheating components will likely cause permanent damage that can lead to much more expensive repairs down the road.

Smoke coming from the vents?

If you notice smoke coming from your supply vents, that is a sign that something larger and more significant than dust and dirt are burning within your heating system.

WARNING: Sometimes something like paper will find itself into your heat exchanger, burner, or coils. This can cause damage and a fire if you are not careful. If there is any smoke, turn your system off immediately and call a professional. They will be able to inspect your heating system and clean everything out if necessary.

Don’t forget to test your smoke alarms and carbon monoxide detectors every 30 days. Make sure there is at least one on each level of the home and outside of every sleeping area.

Common Causes of HVAC Burning Smells

Air Filter

Burning smells are another reminder to change or clean your HVAC air filters. If you have a dirty and clogged air filter, airflow is severely restricted, which puts a lot of extra strain on your motors and fans. One way to prevent burning smells coming from your HVAC system is by remembering the important home maintenance task of replacing or cleaning your air filters every 30-60 days.

Belt-Drive Fan Motor

If you have a belt-drive blower versus a direct-drive blower, the burning smell might be coming from an overstressed or aging rubber belt.

Eventually those rubber belts need to be readjusted or replaced. If you have an overheating belt-drive motor, it can create a rubbery, burning smell. If this is the case, turn your system off and contact a professional HVAC technician as soon as you can.

Overheating Motor

The motor that powers your blower/fan may need to work overtime if the system is old or hasn’t been properly maintained. As a result of an overworked motor, there may be a burning smell. The fix may involve replacing the capacitor (the “battery” that is attached to the side of the motor) or the motor itself.

Burning Electrical Components

A common cause of rotten-egg, sulfuric, or fish-like smells is a dangerous electrical failure somewhere within your electrical system. This may or may not be connected with your HVAC system.

When the plastic components surrounding your wiring start to burn, it can produce a burning smell. This can happen as a result of short circuits, loose screw terminals, defective breakers, or loose/worn electrical connections. Regardless of the cause, turn off power to the circuit and call an HVAC professional or electrician ASAP.

What’s the Best Solution?

If there is a burning smell coming from your HVAC or electrical system, we’re here to help. Contact Pacific Heating & Cooling at (253) 292-3995 (available 24/7) and we’ll send you a qualified professional right away.

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