Why does my furnace smell when I turn it on?

December 10, 2014

Most homes have had their heat running for the last month or two with many homeowners now wondering if the smell emitted from their furnace is normal.  Furnaces emit several fumes and while most are normal (such as the smell when you turn it on for the first time in the season) it’s important to learn the signs of possibly dangerous exhausts or fumes.

Types of Fumes that come from the furnace and the causes:

  1. Burning Smell – This is typically a normal smell resulting from settled dust and debris on the furnace coils burning off as the system heats up.  New furnaces may come with a coating on the coils to prevent rust and corrosion that may also give off a burning smell as the system heats for the first time.  However, if an older furnace has this smell and it lasts for more than a few days after turning your furnace on, there may be a more serious problem that should be handled by a HVAC (Heating, Ventilating, and Air Conditioning) company.
  2. Metal Smell – This smell usually indicates that an electrical component is malfunctioning or has failed; this should be repaired quickly by a professional HVAC company to prevent further damage to the furnace.
  3. Musty Smell – If you smell a musty or mildew type odor coming from your furnace or air supply vents, the culprit may be these fungi growing in an area of moisture build up in the furnace or the ductwork that moves the warm air through your house (for forced air systems).  You should test for mold in this situation as soon as possible with a reliable home kit.  Once you have located the mold, you should take appropriate measures to remove it and preventative action to avoid further moisture build up.  If the musty smell seems to be coming from the ductwork, it may be necessary to bring a professional in to clean your ductwork.  Make sure to close off the vents to prevent any accumulated material in your ducts from getting into the rest of your home and let things settle a little before turning the furnace on when they are finished cleaning the ducts.  Ask about any chemicals that might be used in the duct cleaning to understand what might be going into your ducts as well as what’s coming out.
  4. Strong Rotten Egg Gas Smell – If you have natural gas, leave the house immediately and call your gas/utility company or fire department, as this may be a sign of a gas leak.  Natural gas providers add chemicals to the natural gas so that it can be easily recognized in case of a leak.  The rotten egg smell can also indicate sewer gas from a dry drain trap or a pipe break; you may need to contact a plumber if your gas or utilities company doesn’t find a natural gas leak.

It is important to pay attention to the fumes coming from your furnace and to properly tend to it while it is in use.  Perform a seasonal cleaning to remove some of the accumulated dust and debris before you turn your furnace on and have the furnace checked in the fall to make sure it is operating correctly.  Change the filter before you turn your furnace on and replace it every 4-6 weeks during the winter months or when additional smells or physical symptoms become noticeable.  Don’t forget that when it gets cold outside and your home is closed up to preserve the heat, VOCs can also build up and may cause an air quality problem that wasn’t apparent in warmer weather.  Check your air with a Home Air Check test to make sure your family is safe this winter!