Heat pumps explained — how they work and what they cost in the UK

What is a Heat Pump and How Does it Work?

A heat pump is a highly efficient heating system that works by extracting heat from the air, ground, or water outside your home and transferring it indoors. Rather than generating heat through combustion like a gas boiler, heat pumps move existing thermal energy from one place to another using a refrigeration cycle.

The basic principle involves four main components working together:

• Evaporator: Absorbs heat from the outside source (air, ground, or water)
• Compressor: Increases the pressure and temperature of the refrigerant
• Condenser: Releases the concentrated heat into your heating system
• Expansion valve: Reduces pressure to restart the cycle

This process works even when outdoor temperatures are below freezing, though efficiency decreases in very cold conditions. Modern heat pumps can extract useful heat from air temperatures as low as -15°C to -20°C.

Types of Heat Pumps Available in the UK

Air Source Heat Pumps (ASHP)

Air source heat pumps extract heat from outside air and are the most popular type in the UK. They consist of an outdoor unit containing the evaporator and compressor, connected to an indoor unit that distributes heat through your existing heating system.

ASHPs are suitable for most UK homes and can provide both heating and hot water. Popular brands available through UK installers include Vaillant, Daikin, Mitsubishi, and Worcester Bosch.

Ground Source Heat Pumps (GSHP)

Ground source heat pumps extract heat from the ground through buried pipes containing a water and antifreeze mixture. The ground temperature remains relatively constant year-round at around 8-12°C below 1.5 metres depth, making GSHPs more efficient than air source systems.

However, GSHPs require significant outdoor space for the ground loop installation, either through horizontal trenches (requiring a garden roughly twice the size of your home) or vertical boreholes (requiring specialist drilling equipment).

Hybrid Heat Pumps

Hybrid systems combine a heat pump with a conventional gas boiler. The heat pump handles most of the heating demand during milder weather, whilst the gas boiler provides backup during peak demand or very cold periods. This approach can reduce installation costs compared to a full heat pump system whilst still delivering significant carbon savings.

Understanding Coefficient of Performance (COP) and Seasonal COP (SCOP)

The efficiency of heat pumps is measured using the Coefficient of Performance (COP), which compares the heat output to electrical input. A COP of 3 means the heat pump produces three units of heat for every unit of electricity consumed.

COP is measured under specific test conditions, typically at 7°C outside temperature. Real-world performance varies with weather conditions, with COP decreasing as outdoor temperatures drop.

Seasonal COP (SCOP) provides a more realistic annual efficiency figure by averaging performance across typical UK seasonal conditions. SCOP values typically range from 2.5 to 4.5 for modern heat pumps, with ground source systems generally achieving higher values than air source.

For comparison, gas boilers achieve around 90-95% efficiency (0.9-0.95 COP equivalent), making heat pumps significantly more efficient when the electricity grid includes renewable sources.

Radiators vs Underfloor Heating — Which Works Best?

Heat pumps work most efficiently with heating systems that operate at lower temperatures, as this reduces the work required to heat the refrigerant.

Underfloor Heating

Underfloor heating is ideal for heat pumps because it operates at lower water temperatures (typically 35-45°C) and provides even heat distribution across large surface areas. This maximises heat pump efficiency and creates comfortable living spaces.

New-build homes increasingly specify underfloor heating throughout, particularly on ground floors. However, retrofit installation can be disruptive and expensive.

Radiators

Existing radiators can work with heat pumps but may require upgrading to larger sizes or additional units to compensate for lower water temperatures (typically 45-55°C compared to 70-80°C with gas boilers).

Modern low-temperature radiators designed specifically for heat pump systems offer improved performance whilst maintaining compact sizes. Fan-assisted radiators can also boost output when needed.

Which System to Choose?

The choice depends on your home's existing heating system, insulation levels, and renovation plans. Well-insulated homes with existing underfloor heating or large radiators typically achieve better heat pump performance. Homes requiring significant heating system upgrades may benefit from improved insulation first.

Typical Installation Costs by Type

Heat pump installation costs vary significantly based on system type, home size, and complexity. Prices vary by location and installer, but typical ranges include:

Air Source Heat Pumps

Installation costs vary depending on system size, existing heating infrastructure, and site conditions. Additional costs may include electrical upgrades, planning applications, and heating system modifications.

Ground Source Heat Pumps

Ground source installations typically cost more than air source systems due to groundwork requirements. Horizontal loop systems generally cost less than vertical borehole installations, but require more garden space.

Additional Costs to Consider

• Hot water cylinder replacement or upgrades
• Electrical supply upgrades (often requiring three-phase supply)
• Radiator upgrades or replacements
• Insulation improvements
• Planning permission fees where required
• Annual servicing and maintenance

Government grants may be available to reduce installation costs. Check current eligibility for schemes such as the Boiler Upgrade Scheme before proceeding.

Running Costs Compared to Gas Boilers

Heat pump running costs depend on electricity prices, gas prices, system efficiency, and home heat demand. With electricity typically costing 3-4 times more per unit than gas, heat pumps need to achieve high efficiency to deliver cost savings.

Based on typical UK energy prices, heat pumps with SCOP values above 3.5 can deliver similar or lower running costs compared to gas boilers. However, running costs vary significantly based on:

• Your home's insulation and heat demand
• Local electricity and gas tariffs
• Heat pump system efficiency and sizing
• Usage patterns and temperature settings

Many heat pump users benefit from time-of-use electricity tariffs that offer cheaper overnight rates, allowing systems to pre-heat thermal stores when electricity is less expensive.

The MCS Certification Requirement

The Microgeneration Certification Scheme (MCS) is essential for heat pump installations in the UK. MCS certification is required to:

• Access government grants and incentives
• Ensure installation meets quality standards
• Provide consumer protection and warranties
• Comply with building regulations requirements

Only MCS-certified installers can install systems eligible for government support schemes. Our directory includes 137 MCS-certified installers across the UK, ensuring you can find qualified professionals in your area.

MCS standards cover system design, installation quality, commissioning procedures, and customer handover requirements. This includes heat loss calculations, system sizing, and performance predictions based on your home's specific requirements.

Planning Permission Considerations

Most heat pump installations fall under Permitted Development Rights in England and Wales, meaning no planning permission is required if certain conditions are met:

Air Source Heat Pumps

• Units must be at least one metre from property boundaries
• Ground floor installations only (not on roofs or upper floors)
• Maximum one unit per property
• Unit volume must not exceed 0.6 cubic metres
• No installation on listed buildings without consent

Ground Source Heat Pumps

Ground source installations typically have fewer planning restrictions but may require permission if:

• Installing in conservation areas
• Property is listed or in a World Heritage Site
• Significant groundwork affects protected trees or archaeology

When Planning Permission is Required

Always check with your local planning authority if your installation doesn't meet Permitted Development criteria. Some areas have additional restrictions, particularly conservation areas and Areas of Outstanding Natural Beauty.