Air Source Heat Pump Installation Guide: Complete Process, Costs & What to Expect

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 comprehensive 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: for every 1kW of electricity consumed, ASHPs deliver 3-4kW of heat (known as the Coefficient of Performance, or COP). This 300-400% efficiency makes them far more efficient than even the best gas boilers (90-92% efficient) or electric resistance heating (100% efficient).

Key Components of an ASHP System

• Outdoor unit: Contains evaporator, compressor, and fan. Typically 800mm-1200mm tall, mounted on external wall or ground
• Indoor unit/cylinder: Hot water storage tank (180-300 litres) with integrated heat exchanger
• Distribution system: Radiators or underfloor heating to deliver warmth throughout your home
• Controls: Smart 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. The good news: most 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 dramatically with good insulation:

• Minimum recommendation: EPC rating D or better
• Ideal scenario: EPC rating C or above
• Essential measures: Loft insulation (270mm), cavity or solid wall insulation, double glazing
• Benefit: For the £7,500 Boiler Upgrade Scheme grant, EPC must not recommend loft or cavity wall insulation

If your insulation is inadequate, consider applying for free insulation through ECO4 or GBIS before installing your heat pump.

Space Requirements

ASHPs need physical space for both outdoor and indoor components:

• Outdoor unit: Approximately 1m x 1m footprint, with 1m clearance on air intake side. Can be wall-mounted or ground-standing
• Hot water cylinder: Typically 1.8m tall x 0.6m diameter. Often placed in airing cupboards, utility rooms, or garages
• Clearance considerations: Distance from neighbours (noise), air circulation space, service access

Electrical Supply

Heat pumps require dedicated electrical circuits:

• Most domestic ASHPs run on single-phase 230V supply
• Dedicated circuit required (typically 16-32A)
• May require consumer unit upgrade if current setup is older
• Some older properties may need distribution network operator approval

Heating Distribution System

Heat pumps operate at lower temperatures than gas boilers (45-55°C vs 65-75°C), affecting 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
• Typical outcome: 30-50% of radiators may need replacing with larger models

The Heat Pump Installation Process

Professional ASHP installation typically takes 2-5 days and follows a structured process. Understanding each stage helps you prepare and know what to expect.

Stage 1: Initial Survey and Heat Loss Calculation (Week 1)

An MCS-certified surveyor 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 appropriate heat pump capacity (typically 5-16kW for domestic properties)
• 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

This survey typically takes 2-3 hours. A competent installer will use professional software (MCS calculators) and provide detailed documentation.

Stage 2: System Design and Quote (Week 2-3)

Based on survey findings, the installer creates a comprehensive design:

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

Expect detailed 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) (Week 3-5)

If claiming the £7,500 Boiler Upgrade Scheme grant:

• Installer applies on your behalf through Ofgem portal
• Requires your EPC and proof of replacement heating system
• Approval typically takes 1-2 weeks
• Installation cannot commence until grant is approved

Stage 4: Pre-Installation Preparation (Week 5-6)

Before the installation team arrives:

• Order equipment: Heat pump, cylinder, radiators, controls (2-4 week lead time)
• 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: Installation Day 1-2 - 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: Installation Day 2-3 - 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 refrigerant pipes between outdoor and indoor units through 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: Day 3-4 - System Configuration and Testing

Critical commissioning phase:

• System flushing: Clean heating system to remove debris
• Pressure testing: Check all connections for leaks
• Refrigerant charging: Commission refrigerant circuit (requires 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: Day 4-5 - Handover and Training

The installer provides comprehensive training:

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

Installation Costs Breakdown

Understanding cost components helps you evaluate quotes and identify what's included.

Typical Cost Components (Before BUS Grant)

Factors Affecting Installation Cost

• Property size: Larger homes need bigger systems (8-16kW vs 5-8kW)
• 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 brand: Premium brands (Vaillant, Daikin) vs budget options

Choosing the Right Installer

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

Essential Credentials

• MCS certification: Non-negotiable for BUS grant and quality assurance
• Gas Safe registration: Required if decommissioning gas boiler
• F-Gas certification: Legally required for refrigerant handling
• Building Regulations compliance: Competent person scheme membership
• Public liability insurance: Minimum £5 million cover

Questions to Ask Potential Installers

1. How many heat pumps have you installed? Look for 50+ installations minimum
2. Can you provide references from recent customers? Speak to 2-3 previous clients
3. What heat loss calculation software do you use? Should use MCS-approved tools
4. What warranties do you offer? Expect 5-7 years on equipment, 2 years on labour minimum
5. How do you handle after-sales support? Ongoing support is crucial
6. What's the installation timeline? 2-5 days typical, beware of overly short estimates

Red Flags to Avoid

• No heat loss calculation or cursory assessment
• Pressure to sign immediately
• Quotes significantly below market rate (likely corner-cutting)
• Unable to provide MCS certificate number
• 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 ensures optimal performance and satisfaction.

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 (45-55°C) not hot (65-75°C), but deliver same heat over longer time
• Always-on heating: Best efficiency comes from maintaining steady temperature rather than heating on-demand
• Hot water scheduling: Cylinder typically heated once or twice daily 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 45-55°C vs 65-75°C for gas boilers. They feel warm not hot, but deliver the same total heat over longer periods. Your home should maintain target temperature.

"How much electricity should I expect to use?"

A well-specified heat pump in an insulated home uses 3,000-5,000 kWh of electricity annually for a typical 3-bedroom house. Monitor first winter bills to establish baseline.

Maintenance and Ongoing Costs

Heat pumps require minimal maintenance but regular servicing ensures optimal performance and longevity.

Annual Servicing

Professional service recommended yearly (£100-£150):

• Check refrigerant levels and pressure
• 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: Heating system pressure should be 1-1.5 bar

Expected Lifespan and Costs

• Heat pump unit: 20-25 years
• Hot water cylinder: 15-20 years
• Annual servicing: £100-£150
• Major repairs (rare): £200-£800 if issues arise
• Total 20-year maintenance: £2,000-£3,000 (servicing only)

Maximising Your Heat Pump Investment

To get the most from your ASHP installation:

1. Insulate first: Free insulation via ECO4/GBIS maximises heat pump efficiency
2. Claim BUS grant: £7,500 makes installation affordable
3. Switch to heat pump tariff: Dedicated electricity tariffs save £200-£400 annually
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.

The combination of improving technology, £7,500 government grants, and specialist electricity tariffs means heat pumps are now practical alternatives for millions of UK households. Success requires proper sizing, quality installation, and understanding how to operate the system effectively.

By choosing MCS-certified installers, ensuring adequate insulation first, and learning how heat pumps differ from boilers, you'll position yourself for a successful, satisfying installation that serves your home for 20+ years.