If your heater has been dormant for many months and you turn it on, you're likely to notice a distinctive smell. While some smells are common, others indicate underlying problems with your furnace, heat pump, or electric heater. 

Here are some specific smells you may notice when you turn on the heat. 

Dust Smell

A strong dust smell is normal when you turn on your heating unit after a long time. Most homes in regions that experience changing seasons don't use their heating systems the entire year. As a result, dust and debris accumulate on the heating system's air ducts, heat exchangers, or burners.

So, when you switch on your furnace for the first time, the dust burns off and causes a strong dusty smell that dissipates quickly.

This dusty odor is a normal phenomenon that shouldn't always alarm you. However, if the smell fails to subside after a day or gets stronger as your unit runs, you should check the air filter. A clogged air filter may not filter off all the dust effectively. So, clean or change the air filter if necessary. If the burning smell persists, consider a professional inspection for your heater.

Mildew Smell

A mildew smell is not as annoying, but you shouldn't ignore it. This smell indicates an overly dirty air filter or organic growth in your unit's evaporator coil or ductwork. Sometimes, the mold can burn off with the dust, and the smell will likely disappear. 

However, if the musty odor continues, you should clean or change the air filters to see if it resolves the problem. Schedule professional inspection and cleaning if the smell remains even after you change the air filters.

An experienced repair professional can also clean the system's ductwork and evaporator coil to eliminate organic growth. In addition, they will repair any deteriorated parts that the mold might have ruined.

Electrical Smell

A burning electrical smell could indicate isolated electrical issues with your heater. Sometimes, the smell can emanate from a plastic item or another object trapped in your unit's ductwork. Such items could heat up and begin to smell. A technician can inspect and remove any foreign objects in the ductwork. 

A clogged air filter restricts airflow and causes your system to overheat. Excess heat can melt the wire insulation and lead to sparks that emit a burning odor. If left alone, the melting wires can cause a house fire. Also, an overheating blower motor or a broken heat exchanger can cause a burning smell.

Electrical problems require expert troubleshooting, so switch off your heating unit and call a heating system repair specialist. Don't forget to insist on any constant issues that seem to lower your unit's performance.