Can My Electrics Handle a Heat Pump?

Most York homes can host an air source heat pump on the existing supply without drama. A 100 A main fuse has the headroom for one even with an EV charger, an electric shower and normal household loads running at the same time. A 60 A supply with those same other loads is where the sums stop working, and that's the point at which either load management or a supply upgrade becomes part of the scope. This is about how to check which side of that line you're on, before the MCS firm arrives to size the heat pump itself.

What a heat pump draws

A modern air source heat pump sized for a 3 to 4 bedroom well-insulated home is typically a 6 to 8 kW thermal output unit. That translates to roughly 1.5 to 3 kW of electrical input when running in steady operation, with brief peaks at 5 to 7 kW during startup, defrost cycles, and the first hour after a set-back recovery on a cold morning. In current terms on a 230 V single-phase supply, that is 6 to 13 A in steady state and 22 to 30 A at peak.

The steady-state draw is comparable to an oven or a kettle. The peak draw is what the cable, the circuit protection, and the supply need to be specified for.

Before the installer arrives

Your main fuse rating

Near the meter, before the tails enter the consumer unit, there is a sealed fuse carrier owned by the Distribution Network Operator (Northern Powergrid in York). It is usually circular, black or brown, with the rating printed on the body.

• 100 A is the modern default. Plenty of headroom for a heat pump, an EV charger and other normal domestic loads running together.
• 80 A is common in homes from the 1990s to 2010s. Usually workable for a heat pump with modest other loads. Adding an EV charger as well is where load management starts to matter.
• 60 A is common in older properties, flats and some rural supplies, and is where the sums start to get tight. A heat pump alone is usually fine. Combining it with an EV charger and high-draw appliances means either load management or a supply upgrade.

If you cannot read the fuse rating from the carrier, Northern Powergrid will confirm it over the phone from your MPAN, usually within a few minutes.

Your consumer unit condition

The MCS installer will want to look at the consumer unit before they price the job. They'll be checking for:

• Spare ways, or room to add an extender module, to accept a new 32 A RCBO dedicated to the heat pump.
• A metal enclosure, required under BS 7671 for domestic boards since January 2016. Plastic boards installed before that date are not unsafe, but a significant alteration may trigger a recommendation to upgrade.
• Tails and earthing sized for the new combined load. A 25 mm² tail and a 16 mm² main earth is the modern default; older 16 mm² tails may need upsizing depending on the supply and total load.

If any of those are not in place, a consumer unit upgrade becomes part of the job rather than a separate consideration. My consumer unit upgrade pricing is by circuit count, so it scales predictably, and a Hager board with RCBO-per-circuit and integrated surge protection is the default spec.

What else is on the supply

A rough inventory of the high-draw items that might run at the same time as the heat pump:

• Electric shower (typically 8.5 to 10.5 kW, so 37 to 46 A during use)
• EV charger (usually 7 kW / 32 A when charging)
• Oven and hob (combined 7 to 10 kW on a cooker circuit)
• Immersion heater (3 kW / 13 A if active)
• Tumble dryer, kettle, and general power (peaky, rarely all at once)

A well-designed modern heat pump install uses load management to avoid the heat pump running at peak demand at the same time as the EV charger, for example. On a 100 A supply with sensible load management, there is usually no issue. On a 60 A supply with a 10 kW electric shower and a 7 kW EV charger, the maths stops working without a supply upgrade.

Where the electrical work begins

The MCS installer handles the heat pump itself, the refrigerant circuit, the hydraulic commissioning, and the BUS grant claim. The dedicated electrical circuit from the consumer unit to the heat pump position is either done by the MCS firm (if they hold the electrical competence) or by a separate NICEIC electrician working alongside them.

For most air source heat pumps in a standard domestic install, the electrical scope is:

• A new 32 A RCBO in the consumer unit, or a 40 A for larger units or those with electric backup
• 6 mm² twin-and-earth cable from the board to the heat pump outdoor unit, routed to avoid thermal derating and correctly glanded at both ends
• A local fused spur or isolator at the heat pump position, rated for the unit's maximum draw
• Bonding to the gas and water services confirmed and tested if they have not been checked recently
• Full testing and certification, with an Electrical Installation Certificate (EIC) issued at completion
• Northern Powergrid G98 or G99 notification submitted, depending on the unit size and any solar PV or battery storage on the same installation

DNO notification

Under the UK's Engineering Recommendation framework, G98 is the connect-and-notify route and G99 is apply-and-connect. G98 covers single-phase devices up to 16 A per phase, which catches most small air source heat pumps without an electric backup element; the installer submits the notification after the install, confirming the load. G99 covers larger devices, or combinations where the totals across heat pump, EV charger, solar PV and battery exceed the G98 threshold, and the DNO has to approve the connection before it can be energised.

Northern Powergrid has 11 working days to respond to a G98 notification. For G99 applications the window is longer and usually involves a load flow assessment to confirm the local network can accept the additional demand. I've submitted plenty of G99s for York properties with combined heat pump, EV and battery storage on the same installation. Northern Powergrid are pragmatic about it; the DNO timeline just needs to be in the project plan from day one.

A worked example from a recent York install

A 3-bed 1930s semi in Acomb. Existing 80 A supply, plastic consumer unit from 2008 with a single split-load RCD, no spare ways, 16 mm² tails. The homeowner wanted an 8 kW air source heat pump, a 7 kW EV charger, and to keep the existing 9 kW electric shower.

The electrical scope came out as:

• Consumer unit upgrade to a 12-way Hager metal enclosure with RCBO per circuit and integrated Type 2 SPD, upsized tails and earthing
• Dedicated 32 A RCBO for the heat pump circuit, 6 mm² cable to the outdoor unit position
• Dedicated 32 A RCBO for the EV charger, 6 mm² cable to the front elevation
• G99 application to Northern Powergrid, given the combined loads
• Load management between the heat pump and the EV charger, configured by the charger firmware to pause charging when the heat pump exceeds a set threshold

No supply upgrade needed in the end. Total project ran over 3 days: Day 1 consumer unit upgrade and testing, Day 2 heat pump and EV circuits, Day 3 MCS commissioning of the heat pump with me on site for the final connection and certification.

What to do before you ring the heat pump firm

1. Confirm your main fuse ratingLook at the meter position, or call Northern Powergrid with your MPAN number.
2. Photograph your consumer unitOpen the front flap (without removing the cover) and take a clear photo of the labels and breakers. The MCS firm and the electrician can assess from the picture.
3. List other high-draw loadsElectric shower, EV charger, electric oven, immersion heater. The MCS designer will size the heat pump and any load management against the full picture, not the heat pump alone.
4. Ask the MCS firm who will do the electrical workEither the firm in-house (ask for the certification details) or a separate NICEIC electrician working alongside them. Get clarity before the order is placed.
5. Factor in the DNO timelineG98 is a formality after the install. G99 can add 4 to 8 weeks. Build it into the project plan, not as an afterthought.

Before booking the heat pump survey

Most York homes can host a heat pump on the existing supply. On the ones that can't, a consumer unit upgrade or a supply upgrade usually gets you there. A 20-minute look at the board, the tails and the main fuse before the MCS firm arrives is the cheapest version of this conversation. If an upgrade is needed, better to know it before the estimate lands.