Many homes today are heated by a furnace. They’re more energy efficient than ever, they make your home comfortable and they are widely available. However, they can sometimes develop a problem. If your furnace has started to make a whistling sound, what is causing that?

Dirty Air Filter

A dirty air filter can produce a whistling sound. As it gradually gets clogged with dirt and debris, it has less space for air to pass through. Additionally, a clogged filter makes your furnace work much harder than it should, which leads to breakdowns. Check the air filter monthly and replace it as needed.

Leaking Air Ducts

The problem may not be your furnace. Most air ducts in homes are leaky. Holes and gaps in your ductwork cause unnecessarily high energy bills and can let in rodents. Air can whistle when it leaves these holes and ducts.

Too Small Ductwork

If you hear a whistling sound when your furnace is on, it could be a sign your ductwork was improperly installed. The ductwork may be too small for your furnace and blower. When ductwork is too small, it constricts the airflow through your ducts. This can produce a whistling sound. The only solution to this is to have your ductwork replaced.

Malfunctioning Gas Supply Valve

The gas supply valve controls the quantity of natural gas sent to your furnace. If it’s malfunctioning, the gas can come out under higher pressure, producing a whistling sound.


Natural gas has ethyl mercaptan added to it as otherwise it is odorless and tasteless. Ethyl mercaptan smells like rotten eggs. If you smell this near your furnace, turn off your furnace, leave your home and call an HVAC company for heating repairs.

Mighty Pine Heating & Air in Arvada, CO, can help you when your furnace is whistling. We repair, replace, and tune up heaters and air conditioners. Our company also installs water heaters.

Contact us today to find out more or to schedule an appointment!

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