More Than Swapping Boxes
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Retrofitting a commercial or institutional building with a heat-pump system means more than load calculations and swapping boxes. The building envelope, electrical architecture, existing system, delivery method, and controls must first be examined and evaluated for heat-pump readiness.
An effective heat pump retrofit depends on careful and cooperative planning.
“Success in heat-pump retrofits starts with alignment around the desired outcome — whether the priority is lower emissions, lower energy use, improved comfort, or a broader modernization strategy,” said Stephen Scott, sustainable systems commercialization manager for Trane in Canada. “The strongest projects begin with collaboration across the owner, engineer, contractor, and technology partners, with a shared view of the building’s goals, constraints, and path forward.”
“It usually starts with doing the upfront work — understanding how the building actually performs today and where load can be reduced before introducing new equipment,” said Rob Landes, director of HVAC systems applications and energy modeling at Daikin Applied Americas.
First steps
The existing building envelope is typically the first thing system designers and technicians look at when planning a heat-pump retrofit.
“Buildings today waste roughly 30% of the energy supplied to them,” Scott said. “Any heat-pump retrofit should begin with the opportunity to improve efficiency and overall building performance — not simply replace equipment.”
Kim Bergeron, COO at K.E. Bergeron Mechanical Systems (ACCA bronze member) in Keene, New Hampshire, put it more bluntly: “We don’t want to install heat pumps in leaky buildings and create energy hogs.”
Likewise, the building’s electrical infrastructure also needs to be examined, and perhaps updated.
“The electrical load of the proposed system must be compared to the availability of power from the existing electrical distribution system,” said Ben Kromer, service manager at Rolls Mechanical in Fenton, Michigan.
At times, Kromer continued, past utility bills that document real-world usage can be used to determine whether the building has enough spare capacity for a heat pump system. At other times, an electrical engineer may be called upon to “analyze the existing system and required electrical load of the proposed equipment and then inform us and the client if the existing electrical system is sufficient or will require upgrades.”
Landes pointed out that a dual-fuel system, with a heat pump as the main heating source and a gas furnace for backup heat when the outdoor temperature is extremely low, will draw less electricity than a heat pump with backup electric resistance heating.
Digging into the building data, experts said, is important when examining the building envelope and electrical capacity. Calculating actual heating and cooling loads, looking at the building’s energy use intensity (EUI), and understanding how electricity is used in it are vital.
Many existing buildings, Scott said, don’t perform as they were originally designed to.
“That can lead to oversizing, unnecessary cost, or missed efficiency opportunities,” he said. “Using real building data helps right-size the heat-pump system and identify measures that improve both project economics and long-term performance.”
Existing systems
For Bergeron and Kromer, forced-air systems that include air conditioning are the easiest to replace with heat pumps.
“In general, the ductwork is properly designed for air-source heat pump use,” Bergeron said.
Oil-fired furnaces are more challenging to replace, he added.
“Even when these have originally been designed with central air-conditioning in mind, the ductwork systems usually just can’t support the airflow needed, resulting in hot/cold spots or costly ductwork alteration,” he said.
Kromer took a broader approach to the question of “most difficult,” responding that systems without existing ductwork are more of a challenge.
“They will require a new duct system, or they can use a heat pump with ductless split indoor units,” he said. “This will be more costly than a more centralized system, and these types of heat pumps (with mini splits) also cannot produce the fresh air that is required by most facilities.” Humidification needs will be more difficult to meet without ductwork — but not impossible — and will often require additional equipment, he added.
Landes said existing systems employing packaged rooftop units (RTUs) are the easiest to retrofit, as they’re easily accessible and similar in size to the heat pumps replacing them.
“In these cases, electrical capacity tends to be the primary constraint,” he said.
Certain hydronic systems that use lower supply water temperatures, 130°F or less, are also good candidates, Landes said.
“Those tend to align more naturally with how heat pumps operate, which simplifies integration,” he said.
Scott agreed with Landes about lower-temperature hydronic systems and added that all-electric heating systems and hybrid systems also offer a smoother path.
“In those environments, project teams can often use more of the existing infrastructure, which simplifies the retrofit and improves project economics,” Scott said.
For Landes, older buildings post the biggest challenges.
“Limited electrical infrastructure is a common constraint, but it’s often compounded by systems that rely on higher-temperature heating — like legacy boiler and radiator setups — or don’t have a centralized distribution system to work with,” he said.
Scott described the biggest challenges similarly and stressed the importance of building data in addressing those challenges.
“Building use, occupancy, and load profiles often change over time, and many legacy systems were originally oversized,” he said. “A more data-driven assessment can uncover opportunities to right-size the heat-pump system, reduce unnecessary cost, and improve the likelihood that the project moves forward.”
Kromer and Landes noted that changes in refrigerant policy will likely require components such as indoor coils to be replaced, during heat pump retrofits, with coils that are compatible with newer A2L refrigerants. The indoor coil and the compressor, Landes said, must be properly matched and listed for the refrigerant to be used.
How about controls
In general, said Bergeron, heat pump systems will work better when matched with controls from the same manufacturer.
“Using existing controls negates many of the energy-efficiency characteristics of heat pump systems,” he said.
But there are exceptions. Most ductless systems require proprietary controls, Kromer said. But some existing controls will fit the bill for some systems, he said.
“If a conventional thermostat is to be reused, then some configuration changes will be required for that control to be used with a heat pump,” he said. In a building with a BAS systems, Kromer added, a technician may have to evaluate the current control logic and reprogram it for heat pumps.
“Heat pumps introduce new requirements, like coordinating defrost cycles and responding to varying outdoor conditions, that older control strategies weren’t built around,” said Landes. “Sometimes that can be handled through updates to control logic and sensors; in other cases, upgrading the controls makes more sense to fully support system performance.”
“In retrofit projects, controls are often one of the most important performance enablers because they help manage demand, optimize operation, and ensure the equipment is working as an integrated system,” Scott said.
This article was originally featured in the Summer 2026 edition of ACCA Now Magazine. ACCA members can read the full magazine at https://hvac-blog.acca.org/magazine/.
- More Than Swapping Boxes - October 1, 2026
Posted In: ACCA Now
