Why Does My Furnace Smell When I Turn it On?

By October 25, 2018 April 2nd, 2024 Heating

The cold weather has set in, and you’re ready to finally turn on the heat to keep your home at a comfortable level. However, you might notice an unusual smell coming from your furnace that wasn’t present before you turned it on.

Having a strange smell come from your furnace is common, especially if you haven’t used it in a long time, but it is important to know the difference between a little dust and debris or a serious problem.

If you are ever concerned, you can always depend on us! Design Aire has been offering heating repair, heating maintenance, and furnace replacement/installation services for over 100 years. We know what to look for when a furnace is giving off a weird smell or if you have questions about other common heater problems.

Causes of a Bad Smelling Furnace

In general, a bad smell coming from your furnace is not usually something to stress about if it has been sitting idle for some time. The most common reasons for a bad smelling furnace include:

  • Dirty furnace – Dust and debris burn off when a furnace is first turned on if it has not been cleaned out beforehand, so if the smell is a slightly dusty, burning smell, you can expect that it is coming from that dust burning off.
  • Mold – If the smell coming from your heater is not only dusty, but also musty like an old wet towel, then there could be mold trapped in the furnace in addition to dust. Mold in a furnace can settle in the furnace filter, A/C coil, or on the humidifier panel if one is present in your unit.
  • Trapped toys or overlooked spill – If the burning smell is one you might expect if plastic was burned or if you experienced an electrical short, the cause could be from a toy that got stuck in your vent or some kind of food or drink that spilled near a vent. If you’ve inspected your vents but do not see any foreign objects, call an HVAC technician immediately for help, as the electrical smell coming from your furnace could be more serious!
  • Clogged furnace filter – Sometimes, the an oily smell might come from your furnace and signal a problem like a dirty filter needing replacing. If the odor persists after the filter is replaced, however, it’s important to have an experienced professional come take a look at your HVAC system to make sure the issue is not serious.

How to Fix a Furnace with a Bad Smell

Some general maintenance you can follow to fix a bad smell coming from your furnace might involve:

  1. Clearing dust/debris collected on coils, heater exchange, or interior of the heating unit before it is turned on
  2. Change furnace filter
  3. Check ducts for debris and dust. You can even take a vacuum to them to clear them out.

Of course, not everyone wants to spend the time maintaining their furnace in this way and might prefer to have a tune-up on a periodic basis from a certified technician. Check out our heating maintenance plans to find one that works on your time and your schedule!

Smells That Signal a Serious Furnace Problem

Although most smells from a furnace do not signal a problem is at hand, you should still watch out for a few that might give insight into a larger issue that needs your immediate attention. A few smells to be cautious about and take action on right away include:

  • Electrical burning smell or metallic smell – Heat buildup in your furnace might result in an electrical burning smell or give off a metallic smell. Internal components of your furnace such as electrical wires or damaged rubber pieces may be damaged, and the heat applied to the system is exacerbating the smell. Shut the unit off immediately to prevent further damage or a fire, then contact a technician without delay.
  • Smoke coming from furnace – If your chimney or vents are blocked, it is likely you will experience smoke or notice a smoke detector go off as a reaction to smoke coming out of a heater. As with an electrical smell, shutting off your furnace and then calling a qualified HVAC company to provide a diagnosis is the best course of action.
  • Rotten egg smell – You may have a gas leak if you smell rotten eggs after your furnace is turned on. This can be a faint smell or a very strong smell; however, if it does not go away, shut off your system and call the gas company. They may send someone to help if the problem persists.
  • Chemical smell coming from furnace – A chemical odor in your home after you turn your heater on should not be ignored. If the smell reminds you of formaldehyde, it’s possible the heat exchanger component is damaged. This requires your immediate attention to avoid risk of fire or exposure to carbon monoxide.

Contact St. Louis Heating Experts at Design Aire

If you notice strange smells when you first turn on your heater, then it’s time to check out what’s wrong and fix it right away. The experienced technicians at Design Aire can help! Contact us today to learn about our maintenance and repair services aiding homeowners in the St. Louis and St. Charles areas.