Heat Pump Electrical Supply Upgrade UK 2026

UK Distribution Network Operators (DNOs) require notification or consent before any significant load is connected to the grid, under Energy Networks Association Engineering Recommendation G99 (and its smaller-load sibling G98):

• G98 notification - covers heat pumps drawing under 16A per phase (most UK 5-8 kW domestic units). The installer files the notification with your DNO after install; processing is typically 2-5 business days. No pre-install consent required.
• G99 application - covers heat pumps over 16A per phase OR any 3-phase install. The installer submits the application pre-install; DNO assessment + approval typically 2-4 weeks. Larger heat pumps (10kW+), ground-source installs, and properties needing supply upgrade all fall here.

For typical UK 3-bed semi installs (5-8 kW air-source heat pump on single-phase 100A supply), G98 notification applies + the timeline is post-install paperwork only - no delay to install scheduling.

Your installer assesses three things during the MCS heat loss survey:

• Main service fuse rating. Typically printed on the cut-out (the sealed unit where the service cable enters the property). Common UK ratings: 60A, 80A, 100A. Heat pumps need at least 60A + comfortable headroom; 80A or 100A is the safe baseline.
• Existing electrical load. EV charger (7-22A continuous), electric shower (35A peak), induction hob (32A peak), heat pump (16-32A continuous). The DNO calculates 'maximum demand' based on the household's load profile.
• Service cable size + condition. Older properties may have small or aged service cables (typically 25mm² or smaller) that can't carry the full fuse rating. Visible from the cut-out + the meter cabinet.

Most properties built post-1990 have 100A single-phase + adequate cable. Pre-1990 urban properties + rural properties with long supply cables may need investigation.

Scenario 1: No upgrade needed (most common).

• Existing 80A or 100A fuse, modern service cable, room for additional load.
• G98 notification only.
• Total cost: GBP 0 beyond the heat pump install itself.

Scenario 2: Fuse upgrade only (common for pre-1990 properties).

• Service cable rated for 80A+ but main fuse is 60A.
• DNO replaces the cut-out fuse with an 80A or 100A version.
• Typical cost: GBP 200-400, processed via G99 with 2-4 week consent.

Scenario 3: Service cable upgrade (older terraced properties).

• Existing service cable too small for 80A+ load (25mm² or smaller).
• DNO replaces cable from cut-out to street feed (often requires road excavation).
• Typical cost: GBP 800-1,500, 3-6 week timeline including street work.

Scenario 4: 3-phase conversion (large properties + heavy load).

• Property has high combined load (heat pump + EV + induction cooking + electric shower + workshop).
• DNO converts single-phase to 3-phase supply.
• Typical cost: GBP 2,500-8,000, 6-12 week timeline. Sometimes more if street excavation is extensive.

For typical UK 3-bed semi installs in scenarios 1 + 2, electrical upgrade is either zero cost or a manageable fraction of the heat pump install. Scenario 3 cases need budgeting for; scenario 4 cases need pre-install consultation with the DNO to confirm timeline + cost.

Standard practice across UK heat pump installers:

• BOXT, Octopus Energy, Aira, British Gas, Vaillant Advance partners, Mitsubishi MELCloud installers - all handle G98 notification + G99 application as part of the install package. Quote should include this.
• Smaller independents - typically handle it but check explicitly in the quote. Some pass DNO fees through (~GBP 150-300 for G99 application processing).
• DIY-route or substandard installers - leave the DNO consent to the customer. Avoid this - DNO paperwork errors can void the heat pump warranty + cause grid-side issues.

What you need to provide: existing fuse rating (visible on the cut-out), current household electrical load profile (existing high-load appliances), and the planned heat pump model + kW rating.

For most installs (Scenario 1 + 2), DNO consent runs parallel to install scheduling - no impact on the timeline. For Scenarios 3 + 4:

• Service cable upgrade (Scenario 3): 3-6 weeks added to install timeline. The DNO schedules the cable upgrade independently of the heat pump install date.
• 3-phase conversion (Scenario 4): 6-12 weeks added. Often requires street excavation + can include road-closure permits + reinstatement work.

Plan around this if your install date is time-critical (e.g. before next winter). The good news: most UK installs land in Scenarios 1 + 2 + don't see delays from electrical work.