Heat pump installation day: what happens and how long it takes

What to know first

This summary covers the likely timetable, household disruption and checks before handover.

“Installation day” often means a sequence over several days. This article covers a typical whole-home air-to-water air source heat pump, which heats water for radiators and a cylinder. It replaces a wet central-heating system, where water circulates through radiators or underfloor heating. Air-to-air, hybrid systems that retain another heat source, and ground source projects differ.

The timetable depends mainly on old-system removal, cylinder space, radiator and pipework changes, outdoor-unit siting, electrical work and access. The order can vary, but the agreed design, safety checks, commissioning and handover should still be completed.

How long does a heat pump installation take?

Energy Saving Trust says a standard air-to-water installation typically takes around three days. Extensive radiator or pipework replacement, underfloor heating or a complex building can extend it, and the heating is normally off for most of the fitting period.

The UK government’s installer page says:

These are planning ranges, not promises. The contract should state the expected duration and likely heating and hot-water outage.

What should be settled before the installers arrive?

The technical design should already be complete. The Microgeneration Certification Scheme (MCS) requires a competent building assessment, an on-site risk assessment and the correct Building Regulations and electricity-network process.

Check that the contract identifies removals, radiator and pipe changes, cylinder and outdoor-unit locations, making good, waste removal and any temporary heating. Clear access to radiators, the cylinder position, the fuse box — also called the consumer unit — and the outdoor route. Tell the installer about pets, children or reasonable special requirements.

MCS expects certified installers to explain the timetable, access and delays, protect the property and clean up.

Good to know

changes should be written down — Changes to the design, equipment, cost, performance estimate or timescale should appear in a written contract variation. Significant changes may give the customer a choice to continue or cancel, subject to the contract terms.

What happens during the installation?

This is a common sequence, but trades may complete several stages in parallel.

1. The team confirms the plan

The lead installer checks the agreed equipment locations and pipe routes, protects work areas and isolates services where needed. Raise any mismatch now. Moving a cylinder or outdoor unit can affect pipework, drainage, noise and the final design.

2. The old system is drained and disconnected

For a full replacement, the heating circuit is drained before the old boiler or cylinder is removed. A hybrid or staged system may retain equipment, so follow the quotation.

Disconnecting or removing a gas appliance counts as gas work and needs a suitably qualified Gas Safe registered engineer.

3. The cylinder and indoor equipment are fitted

Most whole-home air-to-water systems use a compatible hot-water cylinder rather than producing hot water instantly like a combi boiler. The installer fits the cylinder and the pumps, valves and controls specified in the design.

4. Radiators and pipework are altered

Heat pumps often use a lower flow temperature than fossil-fuel boilers. Flow temperature means the temperature of water travelling to the radiators.

The design may therefore specify larger radiators or different pipes, although suitable existing parts can remain. The work may require drilling or limited floor access.

5. The outdoor unit is mounted

The team fits the unit on a suitable plinth or manufacturer-approved bracket, maintains the required clearances and connects insulated pipes and cables. It also provides a safe route for condensate, the water produced during normal operation and defrosting.

MCS requires attention to airflow recirculation, vibration and possible nuisance to neighbours.

6. The electrical connection is completed

An electrician connects and tests the heat pump and controls. The installer should already have assessed the electricity supply.

The Distribution Network Operator, or DNO, runs the local electricity network. Some installations can be connected and notified within 28 days; others need approval first. The installer must follow the applicable process.

7. The wet system is flushed and balanced

The installer flushes the heating circuit to remove sediment or debris, refills it and removes trapped air. Radiators are then balanced so water circulates as intended.

8. The complete system is commissioned

Commissioning checks that the system is safe, correctly installed and operating against its design. The installer tests operation, checks for leaks and faults, and records settings and results.

Expert insight

“Trades may overlap and the order may change. The important tests are whether the agreed design is followed, changes are documented and the complete system is commissioned before handover.”

Giles Crosse

Energy Editor

Experienced editor, journalist and communications consultant specialising in consumer energy and low carbon technologies.

• Editor and campaign author for Shell, EDF Energy and Good Energy.
• Consultant to the United Nations and contributor to the World Economic Forum.
• Journalist for Reuters, the BBC, The Economist and The Guardian.

More about Giles Crosse

How much disruption should you expect?

It is usually possible to remain at home, but Energy Saving Trust says heating is generally off during installation, typically for a couple of days. Cylinder, radiator, pipework or floor work can add disruption.

Tell the installer before the start date if an outage creates a particular risk. Agree safe areas for children and pets. MCS expects installers to consider reasonable requirements and put right damage caused by their work within a reasonable time.

Why commissioning matters

A heat pump that starts is not necessarily ready for handover. Commissioning checks the whole system against the design.

Practical checks include operation, leaks, trapped air, radiator balance and controls. Where weather compensation is used, it automatically adjusts heating-water temperature as outdoor conditions change.

What should happen at handover?

The installer should demonstrate the system, explain the main controls and agree any return visit for unfinished work. The handover pack should include safety information, servicing guidance, manuals, guarantees and warranties.

Ask to see normal heating and hot-water settings, the schedule, any boost function and how to recognise a fault. Heat pumps commonly run for longer at lower water temperatures than boilers. The installer should explain the heating curve where one is used.

MCS’s handover template records the equipment, test date, rated capacity, estimated heat demand, design flow temperature and seasonal performance estimate.

Good to know

certificate timings are not aligned — The January 2025 MCS Customer Commitment says the MCS certificate and any relevant Building Regulations and DNO documents should arrive within 30 calendar days. The MCS Installer Agreement dated 1 September 2025 also requires the certificate to be raised within 30 days. A GOV.UK page still said 10 days when checked on 19 August 2026. Ask the installer to confirm its timetable in writing.

What if the work changes, runs late or has defects?

Ask for changes in equipment, design, price or timing to be recorded before extra work proceeds. MCS requires unforeseen work and its effect on cost and timing to be explained through a contract variation.

For a defect, take photographs, keep dated notes and write to the business that contracted with you. Section 49 of the Consumer Rights Act 2015 requires a trader to perform a service with reasonable care and skill.

Citizens Advice’s England guidance says to approach the trader who arranged the work even if subcontractors attended. Use the relevant national consumer service elsewhere in the UK.

An MCS-certified installer should provide a complaints route and signpost the MCS process if necessary.

When might you need other professional input?

Use the contracting installer for design and commissioning questions. Gas work needs a qualified Gas Safe engineer; electrical and network matters need competent electrical professionals and the DNO.

Contact the relevant planning or building-control body, freeholder or landlord where consent remains uncertain. Use the applicable consumer-advice or MCS protection route for an unresolved dispute.

Key takeaways

• A whole-home installation normally takes several days.

• The agreed cylinder, radiator, pipe, outdoor and electrical work determines disruption.

• Agree heating and hot-water outages before work starts.

• Record day-of-installation changes and their cost and timing effects.

• Flushing, balancing, commissioning and training are essential.

• Keep contracts, manuals, warranties, test records and certificates.

Frequently asked questions