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Here's Why Your Furnace Smells Like It’s Burning

by Ultimate Heating & Cooling / January 27, 2022

When it comes to home maintenance issues, burning smells are one of the most alarming things. Even worse is when your heater smells like burning rubber or plastic, or there’s a burning smell coming from vents indoors, and you aren’t sure what’s causing it.


Why Does My Heater Smell Like It's Burning?

Dust, debris, or damage are the usual causes of burning rubber or plastic smells in heating systems. Read below to learn more about why these problems occur and what to do to fix them.


1. Burning Dust When the Heater Is First Turned On

In most cases, dust build-up in the furnace is the most common cause of a burning smell. Dust accumulates throughout the year, and when the furnace is first turned on in winter, it burns the dust. The quantity of dust can vary from year to year too, as drier summers mean there’s less moisture to prevent dust particles from traveling through the air. When furnace dust ignites, it usually smells like burnt plastic or toast and goes away in a few minutes.


Fortunately, furnace dust is rarely a cause for concern as long as the smell dissipates after it burns off. If your furnace hasn’t been used in a while, look for dust before turning it on. Run your furnace for 10 to 15 minutes and wait for the smell to subside. If it persists, switch the furnace off and check if your air filters are clogged or if something else is burning. Have an HVAC professional check it out if you have any concerns. Minimizing dust in your home reduces it in your furnace.

Consider these dust reducing tips:


2. Overheating HVAC System

If something restricts airflow in your HVAC system, this causes internal parts to work harder than normal and eventually overheat. Dirty air filters are usually to blame, so any dust or dirt trapped in them is liable to incinerate when the system overheats. Clogged filters also trap moisture and heat in the ductwork, leading to mold growth, which later burns. This means the smell caused by dirty filters and overheating is often more pungent than burning dust. 


Clean your air filter regularly and replace it every season. It not only prevents overheating but also reduces harmful debris and dust indoors. Failing to change it can also cause your HVAC system to ‘short cycle’, when it runs in a continuous loop of overheating, switching off to cool down, and then automatically restarting. This loop can lead to furnace components wearing out, expensive breakdowns, and burnt smells lingering.

Changing filters is easy, but make sure its MERV rating is compatible with your furnace. Most residential HVAC systems use filters with a 1 to 8 MERV rating. You can learn more about routine maintenance tasks via our guide on how to clean and prepare your furnace for winter.


3. Burning Components

There are several causes of burning parts in a furnace:

  • Foreign objects, such as small plastic caps, food, or toys, can fall in the vents and burn.
  • Worn-out furnace components, such as capacitors or fan belts. The blower motor won’t work properly if either of these fails, causing other internal parts to overheat.
  • Electrical wiring. Of all the problems you can have with your furnace, this one is the most serious as it can lead to a fire. If the wiring fault isn’t caused by general wear and tear, it could be due to incorrect installation. Aside from fire risk, damaged wiring can overheat the blower motor, melt casings, or crack the heat exchanger.


Turn off the furnace. If the smell is largely in one room or vent, remove the duct cover, look for any foreign objects and remove them if you can. If it looks like a furnace component needs replacing or there’s broken wiring, do not repair it yourself, as it can lead to more damage. Get it checked by a qualified HVAC specialist.


In Summary

If you have questions about unusual or worrying burning smells in your HVAC system or want one of our expert technicians to have a look, call us at (720)647-5099 or send us a message

We also offer annual HVAC maintenance plans that give you peace of mind that your HVAC system is getting the care it needs year-round.

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