Air Source Heat Pump Installation Explained

Installing an air source heat pump (ASHP) is one of the most effective ways to decarbonise your home's heating while potentially reducing energy costs. But the process involves more than simply swapping out your boiler. This guide walks you through every step of ASHP installation, from initial assessment to final commissioning, helping you understand what to expect and how to ensure a successful outcome.

What is an Air Source Heat Pump?

Air source heat pumps extract heat from outdoor air and use it to warm your home and provide hot water. Unlike gas boilers that burn fuel to create heat, ASHPs work like refrigerators in reverse, using electricity to move heat from outside to inside.

The key advantage: the Energy Saving Trust says that for every unit of electricity it uses, a heat pump produces three units of heat. Which? puts the typical UK Seasonal Coefficient of Performance (SCOP) at around 3.0, or 300% efficient. That makes heat pumps far more efficient than a gas boiler, which burns fuel, or direct electric heating, which turns each unit of electricity into one unit of heat.

Key Components of an ASHP System

• Outdoor unit: Contains evaporator, compressor, and fan. Mounted on an external wall or on the ground
• Hot water cylinder: Stores hot water, sized to your household's needs
• Distribution system: Radiators or underfloor heating to deliver warmth throughout your home
• Controls: Thermostats, weather compensation, and scheduling systems
• Pipework: Connecting outdoor and indoor units, plus distribution to heating emitters

Pre-Installation: Is Your Home Suitable?

Before proceeding with installation, assess whether your property is ready for an ASHP. Many UK homes can accommodate heat pumps with appropriate preparation.

Insulation Requirements

Heat pumps work best in well-insulated homes. While they can heat any property, efficiency and running costs improve with good insulation:

• Start with the basics: Loft insulation topped up to around 270mm, and cavity wall insulation where suitable
• Then consider: Solid wall or floor insulation and draught-proofing
• Heat loss calculation: The heat pump is sized for your home as it is, so insulate before the survey if you can (see why loft and cavity insulation come first)
• Grant rules: The Boiler Upgrade Scheme grant no longer needs a valid Energy Performance Certificate (since 28 April 2026)

If your insulation is inadequate, check whether you qualify for help through ECO4 or Warm Homes: Local Grant before installing your heat pump. ECO4 runs until 31 December 2026 and work may be fully or partly funded; the Great British Insulation Scheme closed on 31 March 2026.

Space Requirements

ASHPs need physical space for both outdoor and indoor components:

• Outdoor unit: Needs a solid wall or base, with clear space around it for airflow and servicing as the manufacturer specifies. Can be wall-mounted or ground-standing
• Hot water cylinder: Needs a tall cupboard or similar space, such as an airing cupboard, utility room or garage
• Neighbours and access: Think about noise, where the fan will face, air circulation and service access

Planning Permission (England)

Many air source heat pumps on houses in England can be installed under permitted development, without a planning application, if the conditions are met. The rules were relaxed on 29 May 2025:

• The old rule that the unit had to be at least 1 metre from the property boundary was removed
• The size limit for the outdoor unit on a house rose from 0.6 m³ to 1.5 m³
• Detached houses can have up to two air source heat pumps
• The installation must still meet the MCS 020(a) noise standard
• A heat pump used solely for cooling is not covered, and listed buildings and other conditions still apply

Scotland, Wales and Northern Ireland have separate rules, so check with your council. Source: The Town and Country Planning (General Permitted Development) (England) (Amendment) Order 2025.

Electrical Supply

Heat pumps require dedicated electrical circuits:

• Most domestic ASHPs run on a standard single-phase supply
• A dedicated circuit is required
• May require consumer unit upgrade if current setup is older
• Your installer may need to notify or get approval from your electricity network operator

Heating Distribution System

Heat pumps run at lower flow temperatures than gas boilers, which affects radiator sizing:

• Ideal scenario: Underfloor heating (designed for low temperatures)
• Common scenario: Radiators, possibly requiring upsizing in some rooms
• Assessment needed: Heat loss calculations determine if current radiators are adequate
• Possible outcome: Some radiators may need replacing with larger models

The Heat Pump Installation Process

Professional ASHP installation usually takes a few days on site, after a survey and design stage. Understanding each stage helps you prepare and know what to expect.

Stage 1: Initial Survey and Heat Loss Calculation

The installer, who must be MCS certified for the grant, visits your home to conduct detailed assessments:

• Room-by-room heat loss calculation: Measures each space to determine heat requirements using factors like wall construction, glazing, and insulation
• System sizing: Calculates total heat demand to specify the right capacity (the median heat pump installed under the Boiler Upgrade Scheme in April–June 2026 was 8 kW)
• Radiator assessment: Evaluates existing radiators against heat pump temperatures
• Outdoor unit placement: Identifies optimal location considering noise, appearance, and efficiency
• Hot water cylinder location: Determines best position for new cylinder
• Electrical supply review: Checks if upgrades are needed

A competent installer will use recognised heat loss calculation methods and give you the results in writing.

Stage 2: System Design and Quote

Based on survey findings, the installer creates a design:

• Specified heat pump model and capacity
• Hot water cylinder size and specification
• Radiator upgrade requirements
• Control system recommendations
• Electrical work needed
• Detailed quotation with the BUS grant taken off the price (if applicable)

Expect plans showing component locations, pipework routes, and electrical connections. Review this carefully and ask questions about any aspect you don't understand.

Stage 3: Grant Application (If Applicable)

If claiming the Boiler Upgrade Scheme grant (£7,500 in England and Wales, or £9,000 for eligible off-gas-grid homes heated by oil or LPG until 31 March 2027):

• Your MCS certified installer applies on your behalf through Ofgem
• You must own the property and be replacing fossil fuel heating such as oil, gas, electric or LPG
• You no longer need a valid EPC, and there is no income test
• The installer must install and commission the heat pump within 120 days of applying
• Hybrid heat pump systems are not eligible

Stage 4: Pre-Installation Preparation

Before the installation team arrives:

• Order equipment: Heat pump, cylinder, radiators, controls (ask your installer about lead times)
• Plan access: Ensure installers can access loft, outdoor unit location, cylinder position
• Clear spaces: Remove items from areas where work will occur
• Notify neighbours: Courtesy heads-up about temporary noise and activity

Stage 5: Preparation and Removals

Installation begins with preparatory work:

• Old boiler removal: Decommission and remove existing heating system
• Hot water cylinder removal: If you have an old cylinder, it's removed
• Electrical preparation: Install dedicated circuit and isolator
• Radiator removal: Take out radiators being replaced

During this phase, you'll typically have no heating or hot water. Plan accordingly, especially in winter.

Stage 6: Heat Pump Installation

The core installation work:

• Outdoor unit positioning: Mount on wall brackets or ground frame, ensuring secure, level installation
• Indoor cylinder installation: Position and secure hot water cylinder, connect to heating system
• Pipework connection: Run pipes between outdoor and indoor units through an external wall (core drill required)
• New radiators: Install upgraded radiators where needed
• Heating system connection: Connect heat pump to distribution pipework
• Electrical connection: Wire heat pump to dedicated circuit, install controls

Stage 7: System Configuration and Testing

Critical commissioning phase:

• System flushing: Clean heating system to remove debris
• Pressure testing: Check all connections for leaks
• Refrigerant work: Commission the refrigerant circuit where needed (requires an F-Gas qualified engineer)
• First operation: Start system and monitor initial performance
• Weather compensation setup: Configure controls to adjust output based on outdoor temperature
• Hot water programming: Set cylinder heating schedules
• System balancing: Adjust flow rates to each radiator for even heating

Stage 8: Handover and Training

The installer should explain:

• How to use controls and set schedules
• Understanding heat pump operation (why it runs longer than a boiler)
• Adjusting temperatures and settings
• Basic troubleshooting
• Maintenance requirements
• Warranty information and support contacts

You should receive all documentation: MCS certificate (essential for BUS grant), warranty certificates, user manuals, and commissioning reports.

Installation Costs

Knowing typical prices helps you evaluate quotes and spot anything unusual.

Typical Installed Costs (Before the Grant)

Factors Affecting Installation Cost

• Property size: Larger homes with more heat loss need bigger systems
• Radiator upgrades: Number of radiators needing replacement
• Pipework complexity: Distance between outdoor unit and cylinder
• Electrical upgrades: Consumer unit replacement if needed
• Cylinder location: Complex positioning increases labour
• Heat pump model: The make and model you choose

Choosing the Right Installer

Installer quality is critical for heat pump success. Poor installation compromises efficiency, comfort, and longevity.

Essential Credentials

• MCS certification: Required for the BUS grant. Check the installer on the MCS register
• Gas Safe registration: Required for anyone disconnecting a gas boiler. Check the Gas Safe Register
• F-Gas certification: Needed for work on refrigerant circuits
• Building Regulations compliance: Competent person scheme membership, or the work notified to building control
• Public liability insurance: Ask for proof of cover

Questions to Ask Potential Installers

1. How many heat pumps have you installed? Ask for examples in homes like yours
2. Can you provide references from recent customers? Speak to previous clients if you can
3. How did you calculate heat loss and radiator sizes? Ask to see the calculation
4. What warranties do you offer? Ask how long equipment and workmanship are covered, and what the warranty requires
5. How do you handle after-sales support? Ongoing support is crucial
6. What's the installation timeline? Ask how long you'll be without heating or hot water

Red Flags to Avoid

• No heat loss calculation or cursory assessment
• Pressure to sign immediately
• Quotes far below other quotes for the same job (likely corner-cutting)
• Unable to give an MCS certification number you can check
• Vague about specific equipment models
• No written warranty terms

Living with Your Heat Pump: The First Month

Heat pumps operate differently from gas boilers. Understanding these differences helps you get the best from yours.

Key Operating Differences

• Longer run times: Heat pumps run for extended periods at steady output, unlike boilers' short bursts
• Lower radiator temperatures: Radiators feel warm rather than hot, but deliver the heat over a longer time
• Always-on heating: Best efficiency comes from maintaining steady temperature rather than heating on-demand
• Hot water scheduling: Cylinder typically heated at set times rather than on demand

Optimising Your Heat Pump Settings

Getting the best performance requires some fine-tuning:

• Weather compensation: Let the system automatically adjust based on outdoor temperature
• Steady setpoint: Avoid frequent temperature changes. Set one comfortable temperature
• Hot water schedule: Heat water during off-peak electricity hours if on time-of-use tariff
• Don't boost frequently: Boosting reduces efficiency. Size system correctly instead

Common First-Month Questions

"Why is my heat pump running all the time?"

This is normal and efficient. Heat pumps work best running continuously at low output rather than cycling on/off like boilers.

"My radiators feel cooler than before"

Heat pumps run radiators at lower temperatures than gas boilers. They feel warm rather than hot, but a correctly designed system still keeps your home at its target temperature.

"How much electricity should I expect to use?"

It depends on your home's heat loss, how warm you keep it and how much hot water you use. Ask your installer for their estimate of annual electricity use, then compare it with your first winter's meter readings.

Maintenance and Ongoing Costs

Heat pumps need relatively little maintenance, but regular servicing helps keep them running efficiently.

Annual Servicing

A professional service is usually recommended every year and may be a condition of your warranty. It typically covers:

• Check refrigerant circuit and pressures
• Inspect electrical connections
• Clean filters and check airflow
• Test safety controls
• Review performance data
• Check for unusual wear or damage

User Maintenance

Simple tasks you can do yourself:

• Keep outdoor unit clear: Remove leaves, debris, snow accumulation
• Monitor performance: Check app/display for unusual readings
• Listen for odd noises: Report unusual sounds to installer
• Check pressure gauge: Keep heating system pressure within the range your manual or installer gives

Lifespan and Warranties

• Lifespan: Ask your installer how long the heat pump and cylinder are expected to last
• Warranty length: Compare manufacturer and workmanship warranties between quotes
• Servicing: Check whether warranties require annual servicing, and what it costs
• Major repairs: Ask what is covered if a major component fails

Maximising Your Heat Pump Investment

To get the most from your ASHP installation:

1. Insulate first: Help may be available through ECO4 or Warm Homes: Local Grant
2. Claim BUS grant: £7,500 off the upfront price in England and Wales (£9,000 for eligible off-gas-grid homes heated by oil or LPG, until 31 March 2027)
3. Switch to heat pump tariff: With your gas account closed, the Energy Saving Trust estimates savings of around £204–£530 a year against a gas boiler (July 2026 prices)
4. Consider solar panels: Solar electricity can power your heat pump, reducing costs further
5. Use weather compensation: Let the system self-optimise
6. Maintain properly: Annual servicing preserves efficiency

Is ASHP Installation Right for You?

Air source heat pump installation is a significant undertaking but delivers long-term benefits: lower carbon emissions, reduced reliance on fossil fuels, and potentially lower energy costs in well-insulated homes.

Improving technology, the Boiler Upgrade Scheme grant and heat pump electricity tariffs mean heat pumps are now a practical alternative for many UK households. Success requires proper sizing, quality installation, and understanding how to operate the system effectively.

By checking your installer is MCS certified, ensuring adequate insulation first, and learning how heat pumps differ from boilers, you'll give yourself the best chance of an installation that serves your home well for many years.