Heat pumps are among the most efficient HVAC systems. However, they require adequate maintenance to operate at top performance, like any piece of equipment. According to the US Department of Energy, a heat pump with poor maintenance can consume between 10% and 25% more energy than a well-serviced unit.
Heat pumps are complex systems with many interacting components, and they must all operate correctly to deliver efficient heating and cooling. The following aspects are normally checked as a part of heat pump maintenance:
- Adequate airflow through the indoor unit.
- Having a clean drain pan and drain line.
- Adequate airflow through the outdoor unit.
- Adequate refrigerant charge and pressure.
- No refrigerant leaks or crushed ducts.
- Clean coils in outdoor and indoor units.
- Electrical connections in good condition, with no loose or damaged wires.
- Lubricated motors and bearings.
- Correct operation of heat pump controls, especially the thermostat and defrost cycle.
- When applicable, correct operation of the backup heating system.
1) Indoor Unit: Adequate Airflow and Clean Drain Pan
Dust accumulation is the main factor that limits airflow through the indoor unit of a heat pump. Since most dust accumulates on the filter, it should be cleaned at regular intervals and replaced when damaged. However, note that dust can also accumulate on other components, such as blowers and their motors.
Cleaning the drain pan and drain line is also important, since they handle condensate from the indoor unit. There are special cleaning solutions for this purpose, which remove any dirt or mold accumulation.
- Consider that mold thrives with moisture, and it produces unpleasant odors and allergic reactions.
- The drain pan can also get clogged or blocked, and condensate may start dripping.
2) Outdoor Unit: Adequate Airflow and Suitable Location
The outdoor condenser unit of a heat pump must also have adequate airflow. In addition to cleaning the unit at regular intervals, the surrounding area must be kept free of vegetation and other obstacles.
Due to their location, outdoor units are exposed to more factors that can affect airflow. For example, insects and fallen leaves can enter the condenser through air intakes, in addition to the normal accumulation of dust and dirt.
In general, outdoor units should be installed according to the manufacturer’s instructions, avoiding tight spaces where air cannot circulate properly. Reduced spaces also make maintenance tasks more difficult.
3) Handling Refrigerant: Adequate Charge and Leak Prevention
Refrigerant is fundamental for heat pump operation, since it is the heat transfer medium between indoor and outdoor air. Heat is removed from the building during summer, and supplied to indoor air during winter.
A heat pump must be charged with refrigerant according to the manufacturer’s instructions. Otherwise, negative consequences are likely:
- Refrigerant overcharge raises the system pressure and operating temperature, and this can potentially damage the compressor.
- On the other hand, insufficient refrigerant lowers the heat transfer capacity. As a result, the heat pump may be unable to reach a comfortable indoor temperature.
Refrigerant leaks cause a sudden drop in performance, and must be fixed as soon as possible to have reliable heating and cooling. During an inspection, heat pump technicians also check the condition of refrigerant ducts; a crushed or bent duct can hinder refrigerant flow, even if there are no leaks.
4) Indoor and Outdoor Coils: Having a Clean Heat Transfer Surface
The coils are where heat exchange occurs between the heat pump, the indoor air and the outdoor air. Dirt on their surface represents a barrier against heat transfer, and this is detrimental for performance. For this reason, keeping the coils clean is a fundamental maintenance task.
It is common knowledge that the air filters in HVAC units collect dust, and that they must be cleaned at regular intervals. However, the coils are often disregarded: when a thick layer of dirt has accumulated on their surface, there is a notable drop in heat pump performance.
5) Heat Pump Wiring: Keeping Electrical Connections Safe
The electrical circuits that power heat pumps must have wiring of enough ampacity, according to equipment specifications, and they must also have suitable protections. If any of the conductors or circuit breakers are not properly sized, they must be replaced immediately. However, this should not be an issue if you work with qualified HVAC engineers and contractors.
Even when a heat pump is properly wired, connections may be affected over time due to loosening, insulation damage or dust accumulation. Any damaged conductor should be replaced, and connections should be cleaned and tightened at regular intervals.
6) Lubrication: Bearings and Other Mechanical Components
Since heat pumps have moving components, adequate lubrication is important to ensure efficient operation. Poor lubrication increases friction, and this has two negative consequences: energy waste and accelerated wear. In the case of heat pumps, motors and their bearings require special attention – they are used by fans, compressors and refrigerant pumps.
Consider that bearings have a limited service life, and they must eventually be replaced even when lubrication has been adequate. Worn bearings can cause noise and vibration, while reducing efficiency.
7) Heat Pump Controls: Thermostat and Defrost Cycle Operation
Even if all mechanical components and electrical connections are in optimal conditions, a heat pump relies on control signals to operate correctly. For this reason, maintenance tasks should also cover control devices, particularly the thermostat and the defrost cycle control.
- The thermostat should start the correct operating mode, heating or cooling, as needed by the building.
- The defrost cycle should operate as required to remove frost from the outdoor unit. If the heat pump does not defrost when needed, or if the defrost cycle starts too frequently, there may be a control issue.
8) Backup Heating: Adequate Operation
Heat pumps suffer a performance loss when the weather is very cold. They must enter the defrost cycle regularly to remove ice and snow from the outdoor unit, and their energy efficiency also drops. For this reason, many heat pump models include a backup heating system, typically based on resistance heating or natural gas combustion.
If a backup heating system is present, it must also be serviced regularly. Consider that maintenance procedures change depending on the specific type of heating system:
- When combustion heating is involved, maintenance should also cover the gas connection and the exhaust system.
- A resistance heater draws more current than a heat pump of equivalent capacity. In this case, the electrical design must also consider the current drawn by the backup resistance heater.
A heat pump has many interacting parts, and they must all operate correctly to achieve comfort, indoor air quality, and energy efficiency. Heat pump installation and maintenance can be challenging when technicians lack experience with the HVAC technology, hence the importance of working with a qualified contractor.
The HVAC design process also influences maintenance requirements. An optimally sized installation tends to be less demanding in maintenance, and this applies for heat pumps. If you work with a qualified engineering firm, they will consider ease of maintenance when designing the heat pump system.
Michael Tobias PE is a visionary in the construction industry. His passion resonates as the
Founding Principal of New York Engineers, an Inc 5000 fastest growing company. New York
Engineers is the most innovative construction engineering firm focusing on Mechanical,
Electrical and Plumbing (MEP) engineering designs in Chicago and New York. Michael has overseen the design of over 1000 construction projects in all market sectors, including LEED certified and Passive House certified projects. He leads a global team of 50 top performers.