Most homes do not. A 5–12 kW domestic heat pump draws only 7–21 A while running, so an existing 60–100 A single-phase supply normally copes. Upgrades are needed when the property's total maximum demand exceeds the supply fuse, when a 3 kW immersion or resistance backup is added, or when the consumer unit has no spare way for a dedicated protected circuit.
How much electricity does a heat pump actually draw?
Far less than most people assume, because the heat output is three to four times the electrical input. A heat pump described as "8 kW" produces 8 kW of heat; at a seasonal COP of 3 it is consuming about 2.7 kW of electricity — roughly the same as a kettle, and less than an electric shower.
| Heat output at design | Electrical input at design | Running current at 230 V |
|---|---|---|
| 5 kW | 1.6 – 2.0 kW | 7 – 9 A |
| 8 kW | 2.6 – 3.2 kW | 11 – 14 A |
| 12 kW | 4.0 – 4.8 kW | 17 – 21 A |
| 16 kW | 5.3 – 6.4 kW | 23 – 28 A |
Two things change that picture. An inverter compressor starts softly, so there is no large inrush current of the kind an old direct-on-line compressor produced — this is why heat pumps rarely trouble a supply that already runs an electric shower. But a backup immersion or in-line resistance heater does: a single 3 kW element adds 13 A whenever it runs, and that is the load that most often pushes a house over its supply limit.
Does the network operator have to be told?
In Great Britain, yes, and the process depends on the property's total maximum demand including the new heat pump. Under the Energy Networks Association process for connecting heat pumps and EV chargepoints:
- Maximum demand 60 A or less per phase — connect and notify. The installation goes ahead and the network operator is notified within 28 days.
- Maximum demand between 60 A and 100 A — apply first. The installer submits a connection application before installation and the operator confirms within about 10 working days whether the supply can take it.
Other European countries run equivalent schemes; the underlying question is always the same — does the incoming fuse, cable and transformer capacity cover the new peak. Note that this is a demand process, unrelated to the G98/G99 rules that apply to solar PV and batteries because those export power.
When do you genuinely need a supply upgrade?
- The supply fuse is 60 A and the house is already busy — electric shower, induction hob, EV charger. Adding a heat pump plus an immersion element can exceed it.
- The heat pump is 16 kW or larger, or the building has several units. Above roughly 30 A of continuous load, three-phase becomes the sensible answer where it is available.
- The head and meter tails are old or undersized, which the network operator will often insist on replacing at the same time.
- The consumer unit is full, unlabelled or of an obsolete type. This is by far the most common "electrical upgrade" on a heat pump quote, and it is a consumer unit change, not a supply change.
Where the supply is genuinely marginal, load management is usually cheaper than an upgrade: a current-sensing load limiter that sheds the immersion heater when the shower runs, an SG-Ready input that lets a tariff or controller curtail the heat pump at peak times, or simply deleting the resistance backup and sizing the heat pump to cover the full load.
What does the installation itself require?
A dedicated circuit from the consumer unit, sized and protected to the manufacturer's instructions and the national wiring rules, with a means of isolation adjacent to the outdoor unit and a rotary isolator that an engineer can lock off. Manufacturers commonly specify a particular residual current device type — often Type A, sometimes Type B — because an inverter drive can produce DC residual currents that a standard Type AC device will not detect — Type A covers pulsating DC, while smooth DC needs Type B or a dedicated DC detection device. Getting this wrong is a genuine safety issue, not a formality.
Also budget for the small extras that appear on the electrical line of a quote: bonding, a surge protection device, cable route and containment for a long run to a garden-mounted unit, a controller cable and often a heat meter for grant compliance. Together these are a common source of the difference between two quotes — see what actually drives the price of a heat pump installation?
How do I check before I commit?
Read the main fuse rating on the incoming service head (usually 60, 80 or 100 A), count the high-load appliances already in the house, and ask the installer for the heat pump's maximum electrical input, not the nominal figure — including any backup heater. If the arithmetic lands close to the fuse rating, ask for the network operator application to be submitted before the equipment is ordered. Sizing the heat pump correctly in the first place is the cheapest control of all — a Solimpeks heat pump matched to the real heat loss, with no resistance backup bolted on to cover a guess, rarely troubles a domestic supply; see what size heat pump do I need?
Frequently asked questions
Can a heat pump run on a normal 100 amp domestic supply?
Yes, in almost all cases. A 5–12 kW heat pump draws 7–21 A while running, which a 100 A single-phase supply absorbs comfortably alongside normal household loads. Problems arise mainly on 60 A supplies with an electric shower, EV charger and immersion backup all present.
Does a heat pump need three-phase power?
Not for domestic sizes. Single-phase is standard up to roughly 12–16 kW output. Three-phase is worth having for larger units, for commercial installations, or where the single-phase supply is already close to its limit.
Do I need to tell my electricity network operator about a heat pump?
In Great Britain yes. If total maximum demand stays at or below 60 A per phase, the installer connects and notifies within 28 days; between 60 A and 100 A an application must be approved before installation. Other countries operate similar demand-notification schemes.
Does a heat pump need its own circuit breaker?
Yes — a dedicated circuit from the consumer unit with an isolator at the outdoor unit. Manufacturers usually specify the RCD type, often Type A or Type B, because inverter drives can generate DC residual currents that standard devices cannot detect.