Heat Pump Retrofit Timeline UK 2026: 6 Stages

Every UK heat pump install starts with an MCS heat loss survey. The MCS-certified installer visits, measures the property, and produces a detailed heat loss calculation per room. This determines:

• Heat pump capacity (5kW for a 1-bed flat, 7-10kW for a typical 3-bed semi, 12-16kW for a 5-bed detached).
• Radiator sizing per room - existing radiators may be undersized for heat pump flow temperatures.
• Hot water cylinder size based on household size + usage pattern.
• Heat pump location + outdoor unit pad requirements.

Realistic timeline: 1-2 weeks from initial enquiry to survey appointment, plus 3-7 days for the installer to produce the detailed survey report.

What can delay it: peak-season backlog (October-December), rural properties where engineers need to travel further, or properties requiring multiple site visits (e.g. listed buildings).

Once the heat loss survey is complete, the installer designs the specific install:

• Heat pump model selection (Vaillant aroTHERM, Octopus Cosy 6, Mitsubishi Ecodan, etc.).
• Radiator upgrade list per room (if needed for lower flow temperatures).
• Pipework routing from outdoor unit to indoor unit + hot water cylinder.
• Electrical supply assessment (whether DNO consent is needed).

The installer issues a detailed itemised quote. After acceptance:

• BUS grant application submitted by the installer on your behalf. Approval typically 2-7 business days.
• Finance application if using 0% installer finance or green loan.
• Install scheduling - typically 4-12 weeks from quote acceptance to install date depending on installer backlog.

Realistic timeline: 1-3 weeks from survey complete to all paperwork in place + install date booked.

Most UK heat pumps need formal consent from the Distribution Network Operator (DNO) before connection, under the G98 (for smaller units up to 16A) or G99 (larger units or 3-phase supply) regulations. The installer typically handles this:

• G98 notification (smaller heat pumps + standard single-phase supply): notification only, typically processed in 2-5 business days.
• G99 application (larger heat pumps or 3-phase supply): formal application + DNO assessment, typically 2-4 weeks.

If your existing electrical supply is undersized for the heat pump, the DNO may require a supply upgrade (typically GBP 200-1500 for fuse upgrade or supply uprate). This adds 2-6 weeks to the timeline + additional cost.

Most retrofits in standard UK properties don't need supply upgrades. New-build or recent-renovation properties typically have adequate electrical supply already; older properties (pre-1990) may need assessment.

Typical on-site install timing for a UK 3-bed semi:

• Day 1: outdoor unit pad preparation + heat pump unit positioning + initial pipework routing.
• Day 2: indoor unit + hot water cylinder install + remaining pipework.
• Day 3: radiator upgrades (if needed) + electrical work + control system install.
• Day 4: system fill + pressure test + initial commissioning.
• Day 5 (if needed): handover + final commissioning + customer training.

Smaller installs (1-2 bed properties) typically complete in 2-3 days. Larger properties (4-5 bed) + properties requiring extensive radiator upgrades can stretch to 5-7 days.

What you need to prepare: clear access to the install area (no furniture/storage in the way), agreed location for the outdoor unit, decision on whether the old gas boiler stays pluggable as backup for the first winter.

Commissioning is the formal handover from installer to customer:

• Heat pump start-up - first operational use under engineer supervision.
• Flow temperature optimisation - tuning the system for your specific property's heat loss profile.
• Hot water reheat verification - cylinder reaches target temp within manufacturer-spec time.
• Manufacturer registration - heat pump warranty activated against the manufacturer.
• BUS grant final paperwork - installer submits commissioning evidence to Ofgem for grant payment.
• Customer training - how to operate the controls, when to expect higher/lower run-time, how to schedule annual service.

You receive: commissioning certificate, MCS install certificate, manufacturer warranty paperwork, BUS grant confirmation. Keep all documents safe - they're needed for future warranty claims + house sales.

Once commissioned, the heat pump is operational - but the first winter is the most-watched period:

• Run-time pattern - heat pump runs much longer than a gas boiler (continuous low-output rather than burst high-output). This is normal + by design.
• Cost predictability - first electricity bills give real data on actual COP + monthly running cost.
• Comfort observations - any rooms running cooler than expected indicate radiator/UFH sizing issues that need addressing.
• Defrost cycle frequency - cold-weather operation reveals how well the unit handles your local climate.

Most reputable installers leave the existing gas boiler pluggable as backup for the first winter. After one season of stable heat pump operation, the gas boiler can be formally decommissioned + the gas supply contract cancelled.

1. Peak-season installer backlog (October-December). Demand spikes ahead of winter; install dates routinely slip 4-6 weeks vs the off-season. Book in April-July for the fastest install dates.
2. DNO consent for supply upgrade. If your existing electrical supply needs upgrading, expect 2-6 weeks added timeline + GBP 200-1500 cost.
3. Radiator upgrade requirements. Existing radiators often need upgrading for lower flow temperatures. Sourcing + scheduling this adds 1-2 weeks.
4. Planning permission (specific cases). Listed buildings, conservation areas, properties with outdoor unit visibility concerns may need formal planning application (8-12 weeks for decision).