Choosing between a single-phase and three-phase heat pump is not simply a question of buying the larger electrical option.
The correct choice depends on the heat-pump model, its maximum electrical input, the available building supply, other connected loads and the applicable electrical rules. The installer must also consider cable routing, circuit protection, isolation, earthing and any separate backup heater.
For an R290 air-to-water heat pump, the refrigerant does not determine whether the unit uses single-phase or three-phase power. That choice comes from the electrical and compressor design of the specific model.
This guide explains the difference and the checks required before equipment is ordered or installed.
What is a single-phase heat-pump supply?
A single-phase supply delivers alternating current through one live phase and neutral. It is common in homes and smaller buildings in many European markets.
A single-phase heat pump can be appropriate where:
- the selected model is designed for single-phase operation;
- the incoming supply has enough available capacity;
- the main protective device and distribution board are suitable;
- voltage drop can be controlled over the cable route;
- other large electrical loads have been considered.
Single-phase does not mean that electrical planning is unnecessary. A heat pump can be one of the larger continuous electrical loads in a home. The available capacity must therefore be checked rather than assumed.
What is a three-phase heat-pump supply?
A three-phase supply uses three alternating phases. Loads can be distributed across those phases, and larger equipment may be designed to operate directly from a three-phase connection.
A three-phase heat pump may be selected when:
- the model requires a three-phase supply;
- the building already has three-phase service;
- the required electrical load would be unsuitable for the available single-phase connection;
- the wider installation contains several significant electrical loads;
- the project design benefits from distributing loads across phases.
However, three-phase is not automatically more efficient. Heat-pump efficiency is determined by operating conditions and tested performance, not by the number of supply phases alone.
The supply must also be correctly designed. Phase balance, protective devices, conductor selection and the building’s other loads still require assessment.
Single-phase vs three-phase heat pump: the key differences
| Design question | Single-phase heat pump | Three-phase heat pump |
|---|---|---|
| Typical supply | One phase plus neutral | Three phases, normally with neutral where required |
| Common application | Homes and smaller units where adequate capacity is available | Larger models or buildings with an existing three-phase supply |
| Model interchangeability | A single-phase model cannot simply be wired as three-phase | A three-phase model requires the specified three-phase supply |
| Load planning | Available supply capacity and other large loads are critical | Total capacity and load distribution across phases must be checked |
| Cable and protection | Based on maximum current, cable route, installation method and local rules | Based on maximum current per phase, cable route and local rules |
| Efficiency | Not inherently higher or lower because it is single-phase | Not inherently higher or lower because it is three-phase |
| Final decision | Use exact model data and a site electrical assessment | Use exact model data and a site electrical assessment |
The table is a planning overview. It does not replace the product manual or an electrical design completed for the actual installation.
Do not select the electrical supply from thermal capacity alone
Heat pumps are normally described by thermal output: 7 kW, 10 kW, 12 kW or 20 kW, for example. That figure represents heat delivered under specified conditions. It is not the same as electrical input.
Two units with similar thermal capacity may have different:
- voltage and phase requirements;
- maximum electrical input;
- maximum input current;
- compressor and inverter designs;
- backup-heater configurations;
- protective-device requirements.
Therefore, rules such as “all heat pumps above a certain heating capacity need three-phase power” should not be treated as universal.
First determine the building’s heating requirement through a proper heat-loss calculation for heat-pump sizing. Then check the electrical data for the models capable of meeting that load.
Which electrical value should the installer use?
Heat-pump documents can contain several electrical figures. They do not all serve the same purpose.
Rated electrical input
Rated input is measured at a stated test condition. It helps describe performance at that point, but it may not represent the highest electrical demand.
Electrical input range
An inverter heat pump changes compressor speed, so its input varies. The range shows how input can change under the stated operating condition.
Maximum electrical input
Maximum input is a key planning figure. However, the electrical designer must still check whether separate pumps, heaters, controls or accessories have additional supplies.
Maximum input current
Maximum current is relevant to cable and protective-device assessment. It must be used together with the manufacturer’s instructions, starting characteristics, cable route and local wiring rules.
Protective-device data
The manual or nameplate may specify a breaker, fuse, RCD or RCBO requirement. These devices must not be selected solely by applying a generic multiplier to rated input.
The Energy Saving Trust guidance for electricians recommends checking the data badge for operating voltage, maximum current or power input and applicable circuit protection. It also highlights the need to include backup heaters and other electrical loads. Energy Saving Trust toolkits
Tongyi R290 model electrical supplies
The current Tongyi European technical specification dated 26 October 2026 lists the following electrical data:
| Tongyi R290 model | Electrical supply | Maximum electrical input | Maximum input current |
|---|---|---|---|
| TAHMV7 R | 220–240 V / 1 Ph / 50 Hz | 2.80 kW | 12.7 A |
| TAHMV10 R | 220–240 V / 1 Ph / 50 Hz | 4.30 kW | 19.1 A |
| TAHMV12S R | 380–415 V / 3 Ph / 50 Hz | 5.20 kW | 8.5 A |
| TAHMV20S R | 380–415 V / 3 Ph / 50 Hz | 7.60 kW | 13.4 A |
This means the TAHMV7 R and TAHMV10 R are single-phase models, while the TAHMV12S R and TAHMV20S R require three-phase power.
The figures above describe the heat-pump units in the cited specification. They are not complete installation instructions. Before installation, confirm the current model manual, nameplate, country-specific version and any separate electrical accessories.
The latest model documents can be checked through Tongyi’s heat-pump brochure and technical-datasheet downloads.
What should be checked before ordering the heat pump?
Electrical feasibility should be reviewed early. Waiting until the outdoor unit arrives can lead to redesign, supply-upgrade delays or selection of the wrong model variant.
1. Existing supply type
Confirm whether the building has single-phase or three-phase service. Do not rely only on the distribution-board appearance. An authorised electrician should verify the connection and protective arrangements.
2. Available connection capacity
The incoming supply must accommodate the heat pump together with the building’s other loads.
Relevant loads may include:
- electric vehicle charging;
- induction cooking;
- electric showers;
- immersion heaters;
- ventilation and cooling systems;
- battery-charging and energy-management equipment;
- workshop or commercial machinery.
The fact that these loads are not always active simultaneously does not remove the need for a documented maximum-demand assessment.
3. Distribution-board capacity
The board must have the physical and electrical capacity for the required protective devices. Existing earthing, bonding and fault-protection arrangements also need to be verified.
4. Cable route and length
Cable size cannot be selected from current alone. The electrician must consider:
- cable length;
- installation method;
- ambient temperature;
- grouping with other cables;
- conductor material;
- voltage drop;
- protective-device characteristics;
- local regulatory requirements.
For this reason, an article cannot provide a universally correct cable size for a 7 kW, 10 kW or 20 kW heat pump.
5. Network or utility requirements
Some installations require notification, approval or a supply-capacity upgrade from the electricity network operator. Requirements vary by country and connection size.
This should be checked before the equipment order is finalised, especially where a three-phase upgrade may be required.
Does a heat pump need a dedicated electrical circuit?
Heat pumps are normally supplied through a dedicated circuit designed for the appliance and its protective requirements. However, the exact arrangement must follow the manufacturer’s instructions and local electrical rules.
The circuit design may need to include:
- overcurrent protection;
- residual-current protection where required;
- a suitable local isolator;
- surge protection where applicable;
- correct earthing and bonding;
- separation or screening of power and communication cables;
- labelling and commissioning records.
The broader pre-installation steps are covered in Tongyi’s heat-pump installation checklist. This article goes further by focusing specifically on electrical supply and phase selection.
RCD selection must follow the actual heat pump
Modern inverter heat pumps contain power-electronic components. This makes residual-current-device selection more specific than simply installing whichever RCD type is already used elsewhere in the building.
The required device depends on factors including:
- the heat-pump manufacturer’s instructions;
- declared DC residual-current characteristics;
- local wiring regulations;
- the circuit arrangement;
- other protective devices already installed.
The HPA guidance on RCD selection for heat pumps, produced with NAPIT and NICEIC, sets out a structured selection process for domestic installations. It was published on 31 March 2025. HPA UK
It should be treated as UK guidance, not as a substitute for the rules in another country. The final choice must be made by a competent electrical professional using the current product documentation.
Do backup heaters change the calculation?
Yes. Any electric backup heater, immersion heater or tank booster must be included in the electrical-load assessment.
The installer should establish:
- whether a backup heater is built into the selected product;
- whether it is supplied separately;
- its electrical capacity and phase arrangement;
- whether it can operate at the same time as the compressor;
- how the controller stages or limits the load;
- whether it has its own circuit and protection.
Tongyi’s R290 units can support an additional heating system as part of the wider installation design. That does not mean every unit includes an internal electric backup heater. Confirm the actual project configuration before calculating the load.
Does R290 change the electrical requirement?
R290 describes the refrigerant in the sealed refrigeration circuit. It does not specify the building’s electrical phase.
An R290 heat pump may be single-phase or three-phase depending on the model. Likewise, heat pumps using other refrigerants can be offered in either electrical configuration.
The electrical installation must still consider the compressor inverter, fan, circulation pump, controls and any external heaters or accessories.
Tongyi’s R290 inverter air-to-water heat-pump range includes both single-phase and three-phase models. This allows model choice to be matched to the building load and site supply, subject to a complete technical assessment.
Can solar panels or a battery replace the supply check?
No. Photovoltaic panels and battery storage can contribute energy, but they do not remove the need for a compliant grid connection and correctly designed heat-pump circuit.
Solar production varies throughout the day and year. A heat pump must still be able to operate when PV output is low or absent.
Battery and energy-management systems may help coordinate loads. However, their control limits, inverter rating, backup capability and grid interaction must be verified as part of the complete electrical design.
Common electrical-planning mistakes
Choosing from nominal heating capacity alone
Thermal output is not the same as maximum electrical input. Use the electrical table for the exact model.
Assuming a single-phase building can accept any single-phase heat pump
The existing supply may already be heavily loaded. Available capacity and other major appliances must be assessed.
Treating three-phase as automatically more efficient
Phase configuration does not establish COP or SCOP. Use tested performance at the relevant operating conditions.
Ignoring separate heaters and accessories
An immersion heater, backup heater or secondary pump can materially change maximum demand and circuit requirements.
Guessing the cable size
Cable selection depends on more than amperage. Length, route, grouping, voltage drop and installation method all matter.
Selecting an RCD without manufacturer information
Inverter equipment may have specific residual-current characteristics. Use the documented selection process and applicable electrical rules.
Checking the supply after ordering
Electrical feasibility should be part of model selection. A late discovery that three-phase service is unavailable can delay or change the project.
Electrical planning checklist
Before the heat pump is ordered or connected, confirm:
- The exact heat-pump model and country version.
- Required voltage, phase and frequency.
- Maximum electrical input and maximum current.
- Whether backup or booster heaters are present.
- Existing incoming-supply type and capacity.
- Other significant building loads.
- Distribution-board and earthing arrangements.
- Cable route, installation method and voltage-drop assessment.
- Manufacturer requirements for overcurrent and residual-current protection.
- Local-isolation requirements.
- Communication-cable routing and separation.
- Any network-operator notification or upgrade requirement.
- Final test results and commissioning records.
The electrical design and connection should be completed by a competent professional in accordance with local law.
Frequently asked questions
Is a three-phase heat pump cheaper to run?
Not simply because it is three-phase. Running cost depends on heat demand, operating temperature, weather, electricity tariff, system design and heat-pump performance.
Can a three-phase heat pump be connected to a single-phase supply?
No. A model specified for three-phase operation requires the stated three-phase supply. Use an appropriate model or assess a supply upgrade with the relevant professionals.
Can a single-phase heat pump be installed in a three-phase building?
Potentially, if it is connected to the correct phase and neutral arrangement and the load is properly assessed and balanced. The electrical designer must consider the building’s loads across all phases.
What is the difference between rated input and maximum input?
Rated input applies at a stated test condition. Maximum input is a planning limit provided for the model, but separate heaters and accessories may have additional demand.
Does an inverter eliminate starting-current concerns?
An inverter can manage compressor operation differently from direct-on-line starting, but the circuit must still follow the manufacturer’s maximum-current, protection and installation requirements.
Does every inverter heat pump need a Type B RCD?
Do not apply one RCD type universally. Use the manufacturer’s declared residual-current information, the applicable wiring rules and guidance from the relevant electrical authority or certification body.
Who should check the electrical supply?
A competent electrician should assess the supply, circuit and protective arrangements. The heat-pump designer and installer should provide the exact equipment data and coordinate the complete system design.
Match the model to both the building and the supply
A heat pump must satisfy two different requirements.
First, its thermal output must match the building’s calculated heat demand. Second, its electrical requirements must be compatible with the site supply and circuit design.
Single-phase can be entirely appropriate for one project, while three-phase may be required for another. Neither option is automatically superior.
The correct process is to confirm the heat loss, shortlist suitable models, review each model’s maximum electrical data and complete the site electrical assessment before ordering.
For model-specific information, explore Tongyi’s R290 inverter air-to-water heat pumps and the latest technical downloads.
