Heat pump retrofits can make heating more efficient, but replacing a gas boiler also changes where a building gets its energy. The electrical system may need to carry a load it was never designed for.
Imagine an office building warming up on a cold morning. Lights come on, lifts start moving and staff plug in their equipment. Now add a heating system that draws its energy from electricity instead of gas.
That is why heat pump retrofits need more than a suitable place to install the equipment. Engineers also need to check whether the building can supply enough electricity when demand is highest.
Efficient Heating Still Needs Electricity
A heat pump moves heat from one place to another, much like a refrigerator working in reverse. Because it transfers heat rather than producing it entirely from electricity, it can deliver several units of heat for each unit of electricity consumed, as the International Energy Agency explains.
Engineers describe this relationship as the coefficient of performance, or COP. A COP of three means that one unit of electricity delivers three units of heat.
For example, a system supplying 120 kilowatts (kW) of heat at a COP of three needs approximately 40 kW of electrical input, before additional equipment such as circulation pumps is counted.
A gas boiler also uses electricity for controls and pumps, but gas supplies most of its heating energy. Replacing it therefore adds a substantial new electrical load. Replacing an electric resistance heater with a heat pump can have the opposite effect.
The Busiest Moment Matters
Two measurements help explain the challenge. Kilowatt-hours (kWh) describe energy used over time. Kilowatts describe the rate at which electricity is being used.
A building might use less total energy after a retrofit while needing more electrical power during its busiest period.
Consider a simplified example: existing equipment draws 80 kW during morning warm-up. A new heat pump adds 40 kW at the same time. The combined demand becomes 120 kW.
The practical question is whether the cables, switchboard and incoming supply can support that combined load. AIRAH identifies power supply constraints in existing buildings as a key challenge for electrification.
Cold Weather Can Increase the Load
An air-source heat pump takes heat from outdoor air. As outdoor temperatures fall, its efficiency can decline while the building needs more warmth.
Using the earlier example, supplying 120 kW of heat at a COP of two would require approximately 60 kW of electrical input, rather than 40 kW. These are illustrative calculations, and not necessarily predicted performance for a particular unit.
Some systems also use electric backup heaters or need cycles to remove frost from outdoor coils. Natural Resources Canada explains how these operating conditions affect performance. Where electric backup runs alongside the heat pump, designers must include that additional demand.
An Australian Study Shows the Difference
Research co-authored by EIT’s Darren Kelly, Professor Akhtar Kalam and Dr Shasha Wang examined an existing Australian office building.
Its baseline heating and cooling plant reached its governing electrical peak during cooling, at 399 kW. The assessed heat pump configuration produced a calculated winter plant demand of about 957 kW.
That result used an installed heating-capacity boundary of 1,900 kW and specific design assumptions. It was an upper-bound screening assessment, rather than measured demand after installation or a forecast for every building.
The example shows why engineers need to examine electrical capacity alongside heating efficiency.
Existing Heating Equipment Also Matters
The electrical challenge can start with equipment elsewhere in the building.
Some boiler systems circulate very hot water through heating coils, which transfer warmth to the air. A heat pump may operate more efficiently with cooler water, but existing coils may then struggle to deliver enough heat.
Increasing water flow can help in some cases, although it can also increase pumping demand. Other installations may need larger or modified coils.
The Australian Alliance for Energy Productivity’s retrofit guide recommends testing existing heating systems at lower water temperatures before finalizing the retrofit design. This helps establish what the building actually needs.
Plan the Building Around the Upgrade
Start by reducing the heating requirement. Better insulation, improved glazing and appropriate controls can reduce demand, as outlined in the Australian Government’s HVAC guidance.
Then assess when heating overlaps with other equipment. Earlier or staggered warm-up may ease the morning peak. Engineers can also consider thermal storage, such as an insulated hot-water tank, to produce heat earlier and use it later.
These measures may reduce the size of an electrical upgrade, but the design still needs checks against actual equipment ratings and site conditions.
For building owners, the useful question is: can this building deliver efficient heating on its coldest, busiest morning? Answering that before ordering equipment makes the retrofit easier to plan and budget.
References
International Energy Agency — How a Heat Pump Works
AIRAH — Electrification of the Built Environment
Natural Resources Canada — Heating and Cooling With a Heat Pump
Kelly, Kalam and Wang — Electrical Demand Uplift and Coil Performance Constraints in Air-Source Heat Pump Retrofits for Commercial Office Buildings
A2EP / RACE for 2030 — Retrofitting Commercial Buildings With Heat Pumps: A How-to Guide
Australian Government — HVAC Equipment Guide
US Department of Energy — Thermal Energy Storage
This article was published October 20th, 2026 and the content is current as at the date of publication.
