Answer first
Many domestic air-source heat pumps are designed for single-phase supplies. Larger models and unusually high site demand may need three-phase equipment or a supply upgrade, but the installer must assess the actual model and maximum demand rather than decide from floor area alone.
The network operator still needs the installation information. Your installer should check supply adequacy and use the national low-carbon-technology connection process, resolving any required work before the installation date.
ENA says GB network operators provide what a domestic home needs up to a 23kVA cable
View sourceSSEN asks for supply confirmation above this proposed residential maximum demand
View sourceSingle-phase equivalent stated by SSEN alongside that 60A threshold
View sourceAsk FLO to check the whole installation—including electrics
Share your property, current heating and priorities. FLO can arrange the checks needed to turn general heat-pump advice into a complete written proposal.
Single phase and three phase describe the electricity supply
Most UK homes have a single-phase supply. Three phase divides power across three live conductors and can support larger loads or equipment specifically designed for it. The heat pump’s data sheet states the required supply and current.
Do not confuse heat output with electrical input. A 12kW heating output does not automatically require 12kW of electricity because the system moves environmental heat as well as using electrical energy.
The whole property load matters
The installer considers the heat pump, immersion heater, electric shower, cooker, EV charger, battery, solar inverter and other large equipment. They also inspect the cut-out, main fuse, meter tails, consumer unit and earthing arrangements.
Load management may be relevant where two large devices do not need full power simultaneously. It must be engineered and accepted correctly; it is not a reason to hide demand from the network operator.
- Heat-pump running and starting current
- Immersion and backup-heater rating
- Main fuse or cut-out rating
- Existing and planned EV charging
- Electric shower, cooker and other high loads
- Consumer-unit capacity and earthing
What the network operator checks
Energy Networks Association guidance says installers use Connect Direct for domestic low-carbon-technology applications and that the network must be informed under all circumstances. The process assesses whether the local supply can support the installation and identifies remedial work if needed.
SSEN advises that supply capacity must be confirmed when proposed maximum demand is above the cut-out rating or above 60A, stated as 13.8kVA single phase, for residential properties. Network policies and the actual premises still need checking.
When a three-phase upgrade might be considered
A large home with a high-capacity three-phase heat pump, multiple EV chargers or other substantial loads may justify an upgrade. A new development may also choose three phase to plan future capacity.
The network route, cost and timescale are property-specific. Some domestic reinforcement may be provided within published limits, while customer-requested or exceptional work can be chargeable. Do not budget from a neighbour’s experience.
Put the electrical decision in the quote
The proposal should identify the selected model and phase, dedicated circuits, protective devices, isolators, consumer-unit work and who submits the network application. Any assumption about the main fuse or approval should be conditional until verified.
Resolving this before equipment is ordered protects the installation date and avoids paying for a model that cannot be connected as planned.
What to read next
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Questions people also ask
Can a single-phase heat pump heat a large house?+
Potentially. Heating capacity and electrical phase are related through the chosen equipment, not through a simple house-size rule. The design and supply assessment decide.
Who contacts the DNO?+
For a domestic heat-pump installation, the chosen installer normally handles the low-carbon-technology application or notification using the network process.
Is a three-phase upgrade free?+
Not always. The network operator assesses the existing supply and requested capacity. Ask for the site-specific scope and cost before committing.
Evidence used for this answer
Figures are explained in context and links go to the independent source. Prices, tariffs, scheme rules and standards can change, so check the source again before making a financial or technical decision.
- Energy Networks Association: connecting heat pumpsThe national low-carbon-technology notification and network assessment process for domestic installations.
- SSEN: heat-pump electricity connectionsScottish network guidance on supply adequacy, maximum demand and when the network operator needs more information.
- MCS heat-pump design standardTechnical requirements for heat loss, equipment selection, domestic hot water and system design.
- MCS domestic heat-pump guideConsumer guidance covering design, installation, controls, handover and maintenance.