Heat Pump Odors & What They Mean

Jan 11, 2022 | HVAC

Homeowners should never ignore an unpleasant smell coming from their heat pump. This may be an indication that something is up with your heat pump and it’s time to call a technician. In addition to unusual noises and general loss of function, a strange odor is a telltale sign that your heat pump requires repairs. 

Heat Pump Odors

It’s important to recognize the signs before the issue has a chance to get worse. Here A/C and Refrigeration, a leading provider of quality heating and air conditioning services, discusses four common heat pump odors and what causes them.

Musty mildew

A musty smell typically means mold or mildew is growing on wet evaporator coils or in the ductwork. Keep in mind that heat pumps operate at temperatures that can facilitate mold growth. Mold or mildew can be very harmful to those with underlying medical conditions, so be sure not to ignore this issue. It’s best to contact an HVAC technician to prevent spreading bacteria all over your house. 


With traditional gas furnaces, a sulfur-like smell indicates a gas leak. However, your heat pump doesn’t run on natural gas. For this reason, if you think your heat pump smells like sulfur, this might mean a small animal has crawled inside it and died. The smell may be terrible, but it isn’t dangerous. In this case, you should call a technician to eliminate the smell and remove the source of the odor. 

Burning odor

If your heat pump is giving off a burning smell, you might be facing an electrical issue. Burning odors usually point to damaged wiring, failing motor, or melting plastic on electrical wires. These issues should be addressed immediately, or they may lead to expensive repairs. In worst-case scenarios, electrical issues are a serious fire hazard. If you notice this smell, turn off your heat pump at the breaker and call an HVAC technician for heating repair services.

Defrost cycle smell

You might also notice a strange smell coming from your heat pump when it goes into defrost mode. Your heat pump uses defrost mode during the winter. When the air is much cooler, frost can quickly form on the evaporator coils from condensation and disrupt heating. Thus, your heat pump briefly switches to cooling during defrost mode to get rid of the frost. If you want to eliminate the defrost cycle smell, your local technician can help by cleaning the coils.

Now that you know what these odors mean, be sure to contact an HVAC expert to inspect your heat pump as soon as possible. For further inquiries regarding your heating system, get in touch with A/C and Refrigeration. We also offer many services, including heating installation. Call us today at (602) 488-7161 or fill out our contact form to schedule an appointment.