Installation
Heat pump installation: what to expect step by step
Last updated 2026-08-18
Upgrading your home heating system from an old gas, oil, or LPG boiler to an air source heat pump is one of the single best investments you can make to lower energy bills and carbon emissions. However, if you have never experienced a heat pump installation before, you might naturally wonder: How long does it take? How much disruption is involved? Will my water be turned off?
Unlike swapping a gas combi boiler for another combi boiler — which is usually a straight 1-day swap — replacing a boiler with an air source heat pump involves installing an outdoor fan unit, fitting a modern high-flow hot water cylinder, checking radiator sizes, and making electrical connections.
In this comprehensive guide, we walk you through the entire step-by-step heat pump installation journey in the UK for 2026 — covering initial heat loss surveys, grant paperwork, a day-by-day installation breakdown, commissioning, and handover.
Overview: The 4 Phases of Installation
- Phase 1: Survey & System Design (Weeks 1–3): Room-by-room heat loss calculations, electrical DNO check, radiator sizing, quote, and £7,500 BUS grant application.
- Phase 2: On-Site Installation (Days 1–3): Decommissioning old boiler, placing outdoor unit, installing hot water cylinder, plumbing pipework, and electrical wiring.
- Phase 3: Commissioning & Certification (Day 3): Power flushing, filling with glycol antifreeze, balancing flow rates, and issuing MCS certificate.
- Phase 4: Handover & Aftercare: Learning controller settings, setting up smart heating tariffs, and registering manufacturer warranties.
Phase 1: Pre-Installation & System Design
1. The MCS Room-by-Room Heat Loss Survey
Before any physical work begins, an MCS-certified surveyor visits your property. Unlike traditional boiler installers who often estimate sizing based on house type, a heat pump surveyor calculates exact thermal losses for every room in your home based on:
- Room dimensions, wall construction (cavity wall, solid brick, timber frame) and insulation thickness.
- Window types (single, double, or triple glazing) and floor construction.
- Existing radiator dimensions and surface areas.
This survey ensures your new heat pump is sized perfectly (typically 5kW, 7kW, 9kW, or 12kW) to heat your property efficiently on freezing winter days without consuming unnecessary electricity.
2. Electrical Supply & DNO Approval
Because heat pumps operate on electricity, your installer will inspect your consumer unit (fuse box) and incoming main electricity supply.
In the UK, installers must notify your local District Network Operator (DNO) — the company responsible for regional power lines (such as UK Power Networks, National Grid Electricity Distribution, or SP Energy Networks). Most domestic installations fall under "Connect and Notify" rules. If your main fuse is 60A, your energy supplier will upgrade it to an 80A or 100A fuse free of charge prior to installation day.
3. Boiler Upgrade Scheme (£7,500 Grant) Application
Once you accept your installer's proposal, your MCS installer submits a grant reservation request to Ofgem under the Boiler Upgrade Scheme (BUS). Ofgem issues a voucher worth £7,500, which is deducted directly from your final contract price.
Phase 2: Step-by-Step On-Site Installation Timeline
For a typical 3-bedroom semi-detached or detached UK property, physical on-site installation work usually takes 2 to 4 working days with a two-person installation team.
| Day / Time | Installation Stage | What Happens On Site | Homeowner Impact |
|---|---|---|---|
| Day 1 (Morning) | Decommissioning & Site Prep | Old gas/oil boiler drained and removed. Concrete base pad cast or ground mounting feet positioned outside for heat pump. | Old heating isolated. Cold mains tap water remains available. |
| Day 1 (Afternoon) | Outdoor Unit & Wall Core | Heat pump mounted onto outdoor pad. Core drill hole made through external wall for insulated flow/return pipework and power cable. | Brief noise during core drilling (10–15 mins). Site kept clean. |
| Day 2 (All Day) | Indoor Cylinder & Radiators | High-efficiency unvented hot water cylinder fitted in cupboard. Select radiators or TRV valves replaced where specified in design. | Water off intermittently for cylinder connections. Temporary electric heaters provided if cold. |
| Day 3 (Morning) | Electrical Wiring & Controls | Electrician installs outdoor rotary isolator switch, connects consumer unit, fits weather compensation sensor and room thermostatic controls. | Brief power isolation (15–30 mins) while connecting main circuit breaker. |
| Day 3 (Afternoon) | Flushing, Commissioning & Handover | System power flushed, filled with glycol (antifreeze) & scale inhibitor, pressure tested, air bled, and commissioned. Full handover demo. | Heating and hot water fully operational! Walkthrough on controls. |
Phase 3: Commissioning & Certification
Commissioning is the critical phase where raw equipment is transformed into an optimized heating system. Your installer will:
- System Pressure & Leak Testing: The hydraulic circuit is pressurized to 3 bar and monitored to ensure 100% watertight integrity.
- Glycol Antifreeze Addition: Propylene glycol is added to the heating water circuit to protect outdoor pipework from freezing during power outages.
- Flow Rate Balancing: Installers adjust lockshield valves across all radiators to ensure equal heat distribution to every room.
- Setting the Weather Compensation Curve: The heat pump controller is programmed to automatically raise water flow temperatures when outside temperatures drop, optimizing seasonal COP efficiency.
- MCS Certificate Generation: The installer registers the completed installation on the MCS database, generating your official MCS Certificate. This certificate is required for Ofgem grant redemption and guarantees building regulations compliance.
Phase 4: Handover & Aftercare
Before the installation team leaves your property, they will guide you through a complete handover demonstration:
- Operating the Thermostat / App: Showing you how to adjust room temperature setpoints and schedule domestic hot water reheating cycles.
- Understanding "Set & Forget": Explaining why leaving the system running continuously at a steady temperature is far cheaper than turning it on and off.
- Filter Maintenance: Showing you where the magnetic inline filter is located and how your annual service engineer cleans it.
- Smart Tariffs: Recommending dedicated heat pump electricity tariffs (such as Octopus Cosy or OVO Heat Pump Tariff) that offer cheap off-peak rates, cutting running costs by up to 30%.
Frequently Asked Questions
How long does it take to install an air source heat pump in a UK home?
A standard air source heat pump installation in a typical 3-bedroom UK home takes between 2 and 4 working days to complete, depending on whether radiators or internal pipework need upgrading.
Will my heating and hot water be turned off during installation?
Your water will typically be turned off for short periods on Day 1 and Day 2 while the old boiler is removed and the new hot water cylinder and heat pump pipework are connected. Professional installers ensure hot water disruption is kept to an absolute minimum.
Do I need planning permission to install a heat pump?
In England and Wales, most air source heat pump installations fall under Permitted Development Rights provided the installation complies with MCS 020 sound standards and is located more than 1 metre from your property boundary. Planning permission is usually only required for listed buildings or conservation areas.
What electrical work is needed for a heat pump installation?
Your installer will check your main electrical fuse rating (typically requiring an 80A or 100A main fuse) and submit a District Network Operator (DNO) notification before installation. A dedicated electrical circuit and rotary isolator switch are fitted near the outdoor unit.
Ready to take the first step toward your heat pump installation? Check your £7,500 Boiler Upgrade Scheme eligibility and get up to 3 free, no-obligation quotes from local MCS-certified installers — takes under 2 minutes.
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