What's That Smell? 7 Causes Of Odd Odors From Heating Vents

Is there an odd odor coming from your heating vent? There are many causes of heating vent odors, from burning dust to dead animal carcasses stuck in the air ducts. Energy Star recommends having a contractor perform an annual pre-season check-up to ensure that your heating system is running at peak performance. However, many homeowners fail to undergo these annual inspections which can lead to a buildup of dust and debris in the heating system. Here are the most common causes of odd odors in your heating vents.

1. Settled Dust

Loose dust is a common cause of burning smells from the air vent. This most often occurs at the start of the heating season the first time you turn on the furnace. During the summer, dust settles in the furnace heat exchanger. When the furnace is turned on, it gets extremely hot and "burns" any dust that has accumulated. Once the dust has burned off, the smell will usually subside.

2. Fallen Debris

If you have a burning smell that does not subside after one or two uses of the furnace, the odor may be coming from elsewhere. Check the top of the heat exchanger for debris that may have fallen into the duct work. It's possible that this fallen debris is smoldering inside the furnace and putting off a burning smell.

3. Electrical Shorts

If your heating system is old or has not been well-maintained, you may experience problems with electrical shorts. If you have a heat pump or furnace, check the electrical heat kits for wiring shorts. Wiring shorts found in these heating units can cause the wires or insulators to melt, which can emit a smoky smell.

4. Deceased Animals

It's possible that a mouse, rat, bird, or other small critter has died in your air ducts, causing a rancid smell each time your furnace pops on. Dead animals and sometimes even insects can build nests inside air vents and duct work. These animals can make their way into the duct system and often cannot find a way out.

5. Mold or Mildew

Heating vents offer mold and mildew a moist, warm environment in which they can thrive. Mold or mildew can buildup in your heating system due to dampness and cause a musty or moldy smell. When warm air travels through the air ducts, mold spores and bacteria are also pushed through the vents and can cover all surfaces in your home.

6. Air Duct Leak

Air duct leaks can cause a sewer smell to come through your heating ducts and disperse throughout your house. The ductwork for your heating system is likely installed beneath the floors near the plumbing pipes. If there is a small rupture or leak in the septic line or main sewer, the odor can penetrate the air under the house. This odor can get into the ducts and circulate into the home.

7. Paint or Chemicals

Paint or chemical-like odors that come from your heating vent may be present when paint or chemical products are used on or near the air ducts. Even when low-VOC paints are used, painted ducts can become warm and give off an odor. This same odor can be present when a return air register is located near a paint source.

Odd smells in heating systems are common, especially at the start of the heating system when the unit has not been in use for several months. To help prevent unwanted vent smells, it's important to hire a professional to inspect and clean your heating system annually and make any repairs if necessary. For more information about heating vent odors, go to sites and contact your local HVAC professional.