A heat pump retrofit replaces or supplements existing heating and cooling equipment in an occupied building with heat pumps. Unlike new construction, the designer has to work around what is already there: the existing distribution system, structure, electrical service, roof space, ceiling heights and tenants who need heat and cooling throughout the work.
The broader case for electrification is covered in electrification of commercial heating. This guide focuses on the practical work of getting heat pumps into an existing building and making them perform.
Start with an assessment
Before choosing equipment, collect enough information to understand the building as it actually operates.
- Utility data: at least 12 months of gas and electricity bills, and interval electricity data if available, to establish heating energy and peak electrical demand.
- Existing equipment inventory: age, condition, capacity and remaining service life of boilers, RTUs, chillers, air handlers and terminal units.
- Distribution system: hot water supply temperatures, terminal unit types, ductwork condition and any known comfort problems.
- Heating load: a calculated heat loss using current envelope conditions, compared with installed capacity. Existing plants are often oversized by a wide margin.
- Electrical capacity: service size, actual peak demand and available space in switchgear.
- Physical constraints: roof structure, mechanical room space, outdoor locations for units, noise-sensitive neighbours and refrigerant piping routes.
Trend data from the building automation system, if it exists, is valuable. Hot water temperatures and valve positions during cold weather show how much margin the existing system has.
Matching the heat pump to the existing system
The existing distribution system usually determines the most practical heat pump type.
| Existing system | Likely retrofit option | Notes |
|---|---|---|
| Gas-fired rooftop units | Heat pump rooftop units | Check low-ambient capacity and backup heat; curb adapters often needed |
| Boiler with hot water radiation or coils | Air-to-water or water-to-water heat pumps | Supply temperature limits are the main issue |
| Boiler plus chiller with four-pipe distribution | Heat recovery chiller plus air-to-water heat pumps | Captures simultaneous heating and cooling |
| Electric baseboard and window AC | VRF or ductless split systems | Refrigerant charge limits under CSA B52 |
| Water-loop heat pumps with boiler and cooling tower | Replace boiler with air-to-water heat pump or ground loop | Loop temperatures are already low |
| Make-up air units (gas-fired) | Heat pump DOAS with energy recovery | Large outdoor air loads at cold temperatures |
Rooftop unit replacements
Swapping gas-fired RTUs for heat pump units is often the simplest retrofit, and it can be timed with normal end-of-life replacement. Points to check: the heat pump's capacity at local design temperature, defrost behaviour, the size of electric backup heat, unit weight compared with the existing roof structure, and whether the electrical feed can carry the added load. Our guide to replacing rooftop units covers curb, structural and electrical details.
Hydronic systems
Hydronic retrofits depend on whether the building can be heated at lower water temperatures. A practical test is to reset the boiler supply temperature downward in stages during cold weather and monitor comfort complaints and valve positions. Zones that call for full flow at moderate temperatures identify the terminal units that need upgrading. See air-to-water heat pumps for design approaches.
VRF retrofits
VRF suits buildings with many small zones and limited ceiling space, because refrigerant piping is much smaller than ductwork or water piping. The CSA B52 Mechanical Refrigeration Code limits how much refrigerant may leak into the smallest occupied space a system serves, which can force system subdivision or leak detection in small offices and hotel rooms.
Practical issues that derail retrofits
Structure and space
Heat pumps and their outdoor units are often heavier and larger than the gas equipment they replace. Roof framing may need review by a structural engineer. Ground-level units need clear space for airflow, snow clearance and defrost drainage, and should be raised above expected snow depth.
Noise
Outdoor fans and compressors run more hours in heating mode than cooling units did, including at night. Check sound power data against municipal noise bylaws and nearby windows, especially in mixed-use or residential settings.
Defrost and condensate
Air-source heat pumps periodically defrost their outdoor coils, releasing meltwater that can freeze into ice dams on roofs and walkways. Plan drainage paths, heat-traced drains where needed, and keep units away from building entrances.
Ventilation air
Outdoor air at minus 30°C (minus 22°F) is the largest single heating load in many buildings. Adding energy recovery ahead of the heat pump reduces the required capacity and often makes the difference between a workable and unworkable retrofit.
Controls integration
Heat pumps must be sequenced with any remaining boilers or backup heat. Poor sequences commonly run backup resistance or boilers when the heat pump could carry the load, or lock out the heat pump at unnecessarily warm temperatures. Define switchover points, staging and defrost behaviour in the sequence of operations and verify them during commissioning.
Phasing in an occupied building
Most retrofits happen while tenants remain. Common approaches:
- Install the new heat pump plant in parallel with the existing equipment, then switch over during shoulder season.
- Replace RTUs one at a time in spring or fall when heating and cooling loads are low.
- Keep existing boilers in place as backup for the first winter while performance is proven.
- Schedule electrical shutdowns for service upgrades outside business hours.
Commissioning and the first winter
Heat pump systems are sensitive to controls, refrigerant charge and airflow. Commissioning should verify capacity at low ambient temperatures, defrost cycles, backup heat lockouts, and the interaction between heat pumps and any remaining combustion equipment. Because winter performance cannot be fully tested in summer, plan seasonal testing during the first cold period and review trend data through the first heating season. Our building commissioning work typically includes this seasonal follow-up.
Frequently asked questions
Should I replace equipment before it fails?
Ideally the retrofit is planned ahead of failure. Emergency replacements leave no time for load studies, electrical upgrades or incentive applications, and usually default to like-for-like gas equipment.
Can heat pumps provide all the heat in Edmonton or Calgary?
Ground-source systems can. Air-source systems can carry most of the annual heating energy, but a backup source is normally provided for the coldest hours, either electric resistance or retained gas equipment.
Are incentives available?
Often, from utilities, provinces or federal programs, but they change frequently and usually require pre-approval before equipment is ordered.
Key takeaways
- Assess actual loads, equipment condition, electrical capacity and physical constraints before selecting equipment.
- The existing distribution system usually determines the practical heat pump type.
- Supply water temperature, roof structure, noise, defrost and refrigerant limits are the common obstacles.
- Energy recovery on ventilation air can shrink heat pump size substantially.
- Sequence heat pumps carefully with backup heat and verify performance through the first winter.
Talk to an engineer
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