Why Is There a Burning Smell Coming From My Home’s AC Vents? A PHX Tech Explains.

Every year around this time, we get calls from homeowners who are worried about a burnt smell coming from their vents. They want to know if it’s normal or if it’s a sign of a larger problem.

Well, if there’s a burning smell coming from your vents, the problem really depends on whether you’re using heat or air conditioning:

Let’s take a look at both situations to determine whether you need a professional to inspect your system.

Just like anything else, your heating system collects dust over the summer when it’s not in use. So, when your burners come on for the first time, it naturally burns through that layer of dirt and dust.

For the most part, you have nothing to worry about. That dust burns quickly so the smell should disappear after the first few times your heat comes on.

But it’s not normal if:

• This is not the first time you’ve used the heat and the burning smell won’t go away. That means there’s probably something in your furnace or heat pump that’s overheating. Our suggestion? Turn off the heat and call a professional. If something is overheating, it can lead to more expensive damage.
• You see smoke coming from your vents. This could mean that something larger than dust fell onto your heat exchanger/coils. That can damage the furnace if it’s not removed and/or it could cause a fire. Again, turn off the heat and call a professional. They can inspect the system and clean the heat exchanger/coils if needed.

Not using heat and still smell that burning smell? Unfortunately, that’s a bad sign. That most likely means that something inside your AC system is overheating.

If this is the case for you, turn off the AC and have a professional inspect your unit.

Let’s take a quick look at some of the reasons you’d get a burning smell from your AC vents:

One thing you can do before calling a professional is to check your air filter. Change it if it looks like the dirty air filter on the right, in the picture below.

What does a dirty air filter have to do with that burning smell? Well, a clogged air filter blocks the amount of air your system breathes in. And that puts a lot of strain on the system, particularly on the motors. And a motor that has to work harder to get the job done will eventually overheat and produce a burning smell.

If you have a belt-driven blower fan, your fan belt may need to be replaced. The fan belt is made of rubber and helps spin the fan blades that push air through the AC system. If that belt is overworked or working improperly, it can get overheated and create a rubber, burning smell.

Fan motors don’t last forever. Eventually, they get weak and have to work extra hard to do their job. And that leads to them overheating. In some instances, the fix is to replace the capacitor (the cylindrical-shaped “battery” attached to the side of the motor) and in others, you will need to have the motor replaced.

That burning smell could also mean there’s a dangerous electrical failure somewhere in the system. The wires in your AC system are covered in plastic. And an electrical failure, like a motor drawing more current than it should, can quickly burn through that protective plastic covering.