Common Heat Pump Smells: Causes and Fixes

While heat pumps are generally reliable, they may emit various odors that can cause concern to homeowners. Understanding common heat pump smells and how to address them is crucial for maintaining a comfortable and safe indoor environment while preventing more serious issues.

HVAC.com discusses the most common heat pump odors, provides insights into their causes, and offers helpful tips on what you can do to limit these odors.

Common Heat Pump Smells and What They Mean

Heat pumps can produce a range of odors, especially if they haven’t been maintained regularly. Each smell indicates different issues within the system. Some of the most common heat pump smells include:

Musty Odor

A musty or moldy odor indicates moisture buildup and potential mold growth in the system, often in the ductwork, on moist evaporator coils, or within the drip pan. Mold affects indoor air quality and poses health risks if left unaddressed, especially for those with allergies, asthma, and other respiratory illnesses. 

If your heat pump smells musty, identify and eliminate the source of moisture around the heat pump, and contact a professional for mold removal services. Regular heat pump maintenance can help prevent mold.

Burning Smell

A heat pump burning smell often indicates an excess accumulation of dust or debris on the heating elements, which should prompt a call to a qualified HVAC technician. A clogged and dirty air filter can also cause a burning odor. 

Replace the filter and see if the heat pump odor goes away. If it doesn’t, contact an HVAC contractor to inspect the system. Air filters should be replaced about every 2-3 months, or according to the manufacturer’s guidelines.

Electrical Odor

An electrical burning smell from your heat pump may be caused by overheating components, including the motor, damaged wiring, or malfunctioning electrical circuits. An HVAC professional should promptly identify and address the root cause, ensuring your heat pump is safe to operate. Continuing to run the heat pump with a burning smell can lead to a fire.

Chemical Odor

A heat pump refrigerant leak can cause a chemical odor, which may smell like formaldehyde or paint thinner. If you detect such a smell, turn off the heat pump and contact a professional. Based on factors such as the age of your heat pump system and the type of refrigerant it uses, your HVAC contractor can help you determine whether repair or replacement is necessary.

Rotten Egg Smell

A rotten egg smell is common for gas furnaces when they spring a leak. However, since heat pumps don’t rely on natural gas, the sulfur smell may indicate a small animal such as a mouse or chipmunk has gotten inside the system and died. You may be able to remove this yourself; if not, contact an HVAC professional to do so.

Fish Smell

Issues with the system’s wiring can cause overheating and the emission of a fish-like odor. Other potential causes of an unpleasant fish-like smell include an overheating motor or melting plastic components. It is crucial to turn off the heat pump immediately and seek professional assistance to diagnose and address the heat pump problem to maintain a safe and functional system.

Regular Maintenance Can Prevent Heat Pump Smells

The best way to prevent the aforementioned heat pump smells is with regular maintenance and timely repairs. If you operate your heat pump year-round, consider having professional heat pump maintenance performed twice a year, once before the cooling season and again before the heating season. During a heat pump maintenance visit, your technician will clean and calibrate the system and check and inspect the unit for any minor issues that require repair.