Heat pump electrical supply and DNO upgrades for business sites

Why a heat pump adds load

A gas or oil boiler burns fuel and needs very little electricity. A heat pump delivers the same heat using electricity, drawing a fraction of the heat output as electrical input. The ratio is its efficiency, but even at a good seasonal figure the compressors, fans and pumps draw real power, and they do so at the same moment the building asks for the most heat: cold mornings. For a medium or large commercial building that can be a meaningful share of, or an addition to, your existing peak demand.

The extra load matters most when it coincides with the rest of the building’s electricity use, such as lighting, kitchens, IT and any electric vehicle charging. The supply upgrade question is therefore about the combined peak, not the heat pump alone. This is also why the design heat load and the electrical input at the design temperature are worth asking every installer to state.

How to check your site’s supply capacity

Gather three pieces of information before you ask for quotes. Your facilities team, electrician or energy supplier can usually help.

• Incoming supply capacity. The size of the cut-out and incoming cable, usually expressed as amps per phase or kVA. Your DNO can confirm what the connection is designed to carry.
• Maximum import capacity. This is the contractual figure on your electricity connection agreement, in kVA, and may be lower than what the equipment could physically carry. Exceeding it can bring charges or trip protection, and increasing it is a request to your network operator.
• Main switchgear and distribution rating. The main incomer, busbars and the spare ways in your distribution board. A heat pump needs its own correctly rated protective device and cable, and the existing board may have no capacity.

Add your measured maximum demand, from half-hourly meter data if you have it. The headroom between that figure and the capacity of the supply is the first indication of whether an upgrade is likely. A qualified electrician or the installer’s designer should do the calculation, because starting current, power factor and diversity all affect the answer. This site does not carry out surveys.

Single phase versus three phase

A single-phase supply is common on small premises. Larger heat pumps are normally three-phase machines, which spread the load across three conductors and keep the current per phase lower. If your building has a single-phase supply and the proposed heat pump is three-phase, or the total load is high, the connection may need to be upgraded to three-phase. That is a job for the network operator or an independent connection provider, not something the heating installer can do on their own. Electricity North West, for example, lists three-phase upgrades as a separate connection type on its website and says its online quote tool may cover single-phase connections only, directing more complex work to its connections team.

If the site is already three-phase, the question becomes whether the existing capacity per phase and the balance between phases can take the new load. Ask the designer to state the heat pump’s running current and starting current per phase.

Starting current, soft-start and load management

A compressor motor can draw a large surge when it starts. On a weak supply this can cause voltage dips, flicker or nuisance tripping, and it influences how the DNO assesses the connection. Two common measures reduce it:

• Inverter drives and soft-starters. Most modern commercial heat pumps use variable-speed compressors or soft-start arrangements that ramp up smoothly. Ask for the manufacturer’s starting current figure with the drive, not just the running current.
• Load management. Staggered start-up of units in a cascade, limits on electric immersion or backup heaters, and sequencing with other large loads can hold the combined peak below your capacity. A hybrid system that keeps a boiler for the coldest hours also lowers the electrical peak; see the hybrid retrofit guide.

If the heat pump supports a hot water load, remember the recovery period adds to demand, as covered in the hot water heat pump guide.

Asking your DNO or an ICP

Your distribution network operator (DNO) owns and runs the local network up to your meter. Which one serves you depends on where the premises are:

• UK Power Networks: London, the South East and the East of England.
• Electricity North West: the North West.
• Northern Powergrid: Yorkshire and the North East.
• National Grid Electricity Distribution: much of the Midlands, the South West and South Wales. SSEN Distribution: the north of Scotland and central southern England (check yours, the boundaries do not follow postcodes).
• SP Energy Networks: central and southern Scotland. SP Manweb, part of SP Energy Networks, covers Merseyside, Cheshire and North Wales.

The postcode-based boundaries are not always intuitive, so confirm your operator from your meter number or the energy networks look-up before you apply. You can apply to your DNO directly, or use an independent connection provider (ICP), a company accredited to carry out some connection work in competition with the DNO. Either route should explain what a demand connection involves for your site.

Northern Powergrid’s home page points to new and existing connections and to support for customers adding heat pumps, and Electricity North West lists heat pump connections as a connection type. Neither page, as fetched for this guide, gives timescales or costs for your site, and none are given here; this guide has not verified any non-domestic threshold, such as an amperage trigger for a separate application route, so ask your operator which process applies to your load. G99 is the process for connecting generation; a heat pump is demand, so G99 is not the route for the heat pump itself.

What the quote should say about supply

Do not accept a quote that says only “electrical works by others”. Ask each installer to state in writing:

• The heat pump’s rated electrical input, running current per phase and starting current with the drive.
• Whether they have checked the site’s maximum demand and import capacity, and from which data.
• Whether a supply upgrade, new or larger incomer, or three-phase connection is needed, and who applies and pays.
• Who owns the risk if the network operator’s response changes the project, and whether the price is conditional on it.
• The switchgear, cable and protection included in the price, and anything excluded.
• Any load-management or sequencing assumptions the design depends on.

If the installation is within the Boiler Upgrade Scheme (single unit up to 45 kWth or multi-unit system up to 70 kWth, see the GOV.UK scheme page), the installer applies on your behalf, but the supply question remains yours to settle. Allow for this in your project plan rather than treating it as a late surprise, and check installers’ credentials on public registers before you sign.