What is That Strange Smell When the Heat Turns on & What Does it Mean?

Strange smells coming from the furnace or heater are not something that should be ignored. If you turn the heat on and things smell a bit off, it’s wise to investigate the cause of the odor.

Prompt attention can help prevent both fire and the inhalation of toxic fumes from a malfunctioning furnace. It is important to remember not all strange smells are dangerous, and many have completely innocuous causes.


Arizona is a dry and dusty climate. Dust and mold can accumulate within the system as it sits idle. When you turn the furnace on, it circulates that dust and mold throughout the system, creating a musty, dirty smell.

In most cases, this dust or mold will burn off and the odor will go away. However, if it persists, it is a good idea to have the vents vacuumed to remove any stubborn deposits.


The area around a furnace should be clean and clear of any combustible debris. Wood, paper, cardboard and plastic should be kept well away from the furnace at all times.

If you notice any burning smells, you should turn the heat off and locate the source of the burning material before turning the furnace back on again.

Clogged Air Filters

One of the most common reasons for funny smells when you turn on the heat is the filter is clogged. When filters are clogged, they don’t function efficiently. Changing the filter will resolve the problem.

Faulty Unit Components

Faulty components often generate an electrical smell that is sharp and easily identifiable. This can be caused by loose wires, overheating motors, cracks in the heat exchanger or foreign objects that have damaged the furnace’s internal components.

You Can Visibly See Smoke

If you have an oil furnace, the smell of smoke is something that can occur if the puffback is damaged or if there are leaks in the system. If you notice smoke, the heat should be shut off immediately to prevent the risk of fire. It is not something you should attempt to repair yourself.

Need Help? Contact the Professionals at Day & Night Air Today!

Day & Night Air can help you resolve any smoky, musty or dusty odors that are coming from your furnace. We invite you to contact us at 602-497-4662 to learn more about our services and to schedule a service call that will help clear the air within your home.