Heat pumps have annually outsold gas furnaces for several years now, and with the recent introduction of more high-efficiency, cold-climate, air-source heat pumps, that trend is likely to continue.
Increasing numbers of heat pump installations will almost certainly lead to increasing numbers of installation mistakes, especially when overworked technicians are pressed for time and HVAC contractors are struggling to find enough qualified workers. Installation mistakes can lead to poor comfort control, lost system efficiency, equipment failure, and more callbacks.
“The industry is going through massive changes, and integrators are being pressed to adapt faster than ever before,” said Victoria Garcia Massimo, North American operations manager at Airzone Control, which makes HVAC control products that integrate with heat pumps. “As the HVAC industry rapidly evolves with the adoption of inverter-driven heat pumps and integrated control systems, it’s critical that installers stay up to date.”
To that end, The ACHR NEWS contacted Massimo and experts from several other OEMs to ask about mistakes that are commonly made when air-source heat-pumps are installed in homes — and how to avoid those mistakes. Here’s what they had to say.
Manual J Is The Way
Failure to perform an ACCA Manual J, or a similar load calculation, is at the top of many experts’ lists of heat pump installation mistakes, whether the system is ducted or ductless.
“The most prevalent mistake is neglecting to perform a comprehensive load calculation before system selection and installation,” said Keanna MacDonald, a technical and product engineer in North America for heat pump manufacturer Viessmann. “Without accurate load assessments, systems may be improperly sized, leading to inefficiencies, increased wear, and compromised comfort levels.”
A Manual J determines the heating and cooling requirements of a detached, single-family home by estimating its summer heat gain and its winter heat loss, taking into account factors like the climate, occupancy, building construction, insulation, and windows and doors. There is also industry-approved software for performing load calculations.
AT HOME: The outdoor unit of a Viessmann heat pump attached to the side of a home. (Courtesy of Viessmann)
“Always conduct a Manual J load calculation or equivalent to determine the precise heating and cooling requirements of the space,” MacDonald said. “This ensures the selected heat pump system matches the specific needs of the residence, optimizing performance and energy efficiency.”
Mark Loewes, a district technical representative at Rheem Manufacturing Co., said it’s a mistake to assume that because a house has an existing 3-ton system, a 3-ton heat pump system should replace it. “This may not match the home’s load during mild and extreme weather conditions, increasing energy costs and shortening the life of the equipment,” Loewes said. A load calculation is called for.
Casey McConnaughy, a regional technical service manager for ducted systems at Johnson Controls, said oversizing a heat pump system is a common mistake that can lead to poor dehumidification and reduced comfort in cooling mode. A load calculation is the answer here, too.
“To avoid oversizing, it is important to size equipment for the cooling load rather than heating load — even in colder regions,” McConnaughy said.
In addition, McConnaughy said, backup heating elements, if used with a heat pump, also must not be oversized. Again, a load calculation is key.
“When oversized, the backup heat source may operate at a higher capacity than necessary, which can drastically increase utility costs. Do not ever engage more electric heat than necessary during a heat pump defrost cycle,” McConnaughy said.
COLD-CLIMATE TESTED: A Midea cold-climate heat pump in chilly conditions. (Courtesy of Midea)
“Sizing is the most common mistake, as bigger is not better and can lead to short cycling and unhealthy relative humidity levels in the home,” said David Rames, senior product manager at Midea. “On the other hand, undersizing a heat pump can lead to excessive electric auxiliary heat strip usage in colder climates, greatly reducing efficiency and raising homeowner utility bills.”
Get Ducts In A Row
It’s a mistake to take for granted that existing ductwork will be compatible with a new heat pump system, experts said.
“Many installers assume the legacy duct system is adequate for new inverter-driven equipment, which can lead to poor airflow, inefficiency, and premature equipment wear,” said Massimo. “The solution is proper planning: Always conduct a thorough review of the existing duct system and redesign it if necessary to match the manufacturer’s airflow specifications.”
“Not doing a thorough duct inspection or sizing inspection can result in the unit not operating at full efficiency or capacity,” said Loewes. “To avoid this, the best practice is to do a static pressure and airflow test to evaluate the current duct system and adjust as needed.”
Rames recommends that, in addition to a load calculation, heat pump installers conduct a Manual D to determine optimal duct sizing and design, along with a Manual S to determine proper equipment size.
Refrigerant System Do’s And Don’ts
Viessmann’s MacDonald said an incorrect refrigerant charge during the installation of a heat pump on a ducted system is another common mistake, and can compromise efficiency and system longevity.
“An overcharged or undercharged system may not provide the desired comfort levels and can strain the compressor,” she said.
“Use precise refrigerant charging techniques, such as the superheat or subcooling methods, as recommended by the manufacturer,” MacDonald added. “Always refer to the manufacturer’s specifications for the correct refrigerant type and charge amount.”
Rames and Steven Southers, a senior technical support and post-sales manager for ductless systems in North America for Johnson Controls–Hitachi Air Conditioning, said using improper refrigerant lines, and installing refrigerant lines incorrectly, are common mistakes made during the installation of ductless heat pump systems.
“Technicians should stay within the manufacturer’s recommended minimum and maximum lengths to ensure the ideal performance. Lines should be free of kinks or sharp bends which can restrict refrigerant flow, and both liquid and gas lines should be insulated to reduce condensation and energy loss,” Southers said. “Additionally, checking flare connections and proper torquing can help prevent refrigerant loss.”
“Excessive line length or sharp bends can lead to system inefficiencies and even compressor failure,” Rames said. “Following manufacturer guidelines on maximum line lengths, elevation differences, and appropriate flare techniques is key.”
Loewes, at Rheem, said improper brazing of refrigerant lines is another big mistake and can lead to leaks and debris in the refrigerant system and shorten compressor and component life.
FIELD TEST: This Rheem heat pump was tested in the field during the U.S. Department of Energy’s multi-year Cold Climate Heat Pump Technology Challenge. (Courtesy of Rheem Manufacturing Co.)
“Proper connection preparation, such as deburring and cleaning of the connection site, as well as using the right torch, proper brazing rods, and flowing nitrogen would avoid this problem,” Loewes said.
Attention To Indoor Units
Placing indoor units in direct sunlight, or where there are obstructions or other heat sources, is a mistake that can cause uneven temperatures and increase energy use.
“Install indoor units in central locations away from heat sources, direct sunlight, and obstructions,” MacDonald said. “Ensure that the airflow from the unit is not impeded and can circulate freely throughout the space.”
“If the wall-mounted unit is installed too high or too close to a ceiling or corner, airflow distribution suffers,” Rames said.
Oversizing indoor units is a “frequent and costly mistake in ductless installations,” Massimo said.
“Because the smallest ductless units typically start at 6,000 Btus, it’s easy to assign too much capacity to a small zone. This results in short-cycling, poor humidity control, and user discomfort,” she said. “The key to avoiding this mistake is strategic design: Plan carefully and consider how unit placement and airflow (e.g., through open doorways) can efficiently serve multiple rooms with fewer, right-sized indoor units.”
Inadequate electrical connection is another mistake that affects the performance of indoor units, Southers said. The heat pump manufacturer’s guidelines for electrical connections should be followed, he said.
“Each mini split system needs its own dedicated circuit and disconnect box with all components properly grounded,” Southers said.
System Commissioning
Even after a heat pump system is in place, improper setup and commissioning can affect its performance, Massimo said. Take the time to do it right.
“Inverter heat pumps often rely on proprietary communication protocols and are not universally compatible with all thermostats or control systems. If commissioning is rushed or performed without the proper tools, critical settings may be missed,” Massimo said. “These issues can be avoided by using manufacturer-approved setup tools, allocating sufficient time for commissioning, and documenting the process to ensure accountability and long-term performance.”