Types of Air Source Heat Pumps

Air source heat pumps (ASHPs) come in several forms, and choosing the right one is essential for achieving efficient, reliable heating in the UK. Factors such as property size, insulation levels, available outdoor space, local climate and your existing heating system all play a major role in determining the best option.

Below is a clear, expanded breakdown of the main types of ASHPs used across the UK, with practical explanations and guidance for homeowners.

Related Reading - What is an Air Source Heat Pump

1. Monobloc Air Source Heat Pumps

A monobloc system contains the entire refrigeration circuit within a single outdoor unit. Only insulated water pipes run into the property, making the setup straightforward and well suited to most UK homes.

How It Works

• The full heat pump assembly, including the compressor, heat exchanger and refrigerant system is housed outside.

• The outdoor unit heats water directly and pumps it through the home’s radiators or underfloor heating.

• An indoor hot water cylinder stores domestic hot water for taps and showers.

• Because only water travels indoors, there are no refrigerant lines entering the home.

Advantages

• Simple installation: No indoor refrigerant work means fewer specialist requirements and shorter installation time.

• Lower upfront cost: Generally cheaper than split systems both in equipment and labour.

• Versatile application: Works well for the majority of UK housing stock, from older terraces to modern builds.

• Great for UK climate: Performs efficiently in mild, damp conditions typical of the UK.

Considerations

• The outdoor unit should be placed close to the property to minimise heat loss through water pipes.

• In extremely cold climates, monobloc units may not match the peak efficiency of higher-end split systems.

• Space for a hot water cylinder is still required indoors.

Best For

Most UK homes, including semis, terraced houses, bungalows, new builds and retrofits seeking a simple, cost-effective solution.

2. Split-System Air Source Heat Pumps

A split system separates the heat pump components between an outdoor unit and an indoor hydrobox. Refrigerant pipes connect the two, similar to an air-conditioning system.

How It Works

• The outdoor unit captures heat from the air.

• Refrigerant carries this heat indoors to the hydrobox.

• The hydrobox generates warm water for heating and domestic hot water.

• Because crucial heat-transfer components are inside, efficiency remains high even in colder temperatures.

Advantages

• Higher efficiency in colder weather: Better suited for regions where winter temperatures drop significantly.

• Quiet operation indoors: The loudest components remain outside.

• Flexible indoor placement: Hydrobox can be installed in a loft, utility room or plant area, freeing up living space.

• More precise system control: Useful for larger or more complex heating layouts.

Considerations

• Installation requires an F-Gas certified engineer to work safely with refrigerant lines.

• Slightly higher installation cost due to additional components and set-up complexity.

• More parts mean a slightly longer installation timeframe.

Best For

• Homes in colder areas such as Scotland or Northern England.

• Properties prioritising maximum efficiency and performance.

• New build homes, extensions or major renovations where system design can be planned from scratch.

3. Air-to-Water vs Air-to-Air Heat Pumps

Air-to-Water Heat Pumps (Most Common in the UK)

These systems heat water for radiators, underfloor heating and hot water cylinders. They are considered the standard choice for UK homes.

Why They Are Popular in the UK

• Compatible with wet heating systems: Works with existing radiators (although some may require upsizing).

• Provide heating and hot water: A whole-home replacement for gas or oil boilers.

• Eligible for grants: Such as the Boiler Upgrade Scheme (BUS).

• Efficient at low water temperatures: Ideal for UK energy-saving standards.

Air-to-Air Heat Pumps

Instead of heating water, these units heat and circulate warm air throughout the home using internal fan units.

Advantages

• Lower installation costs: No need for radiators, pipework alterations or a hot water cylinder.

• Built-in cooling: Works like air conditioning in the summer.

• Highly efficient for space heating: Rapid warm-up times.

Limitations

• No domestic hot water: Cannot replace a boiler entirely.

• May require multiple indoor units: One per room or zone for full coverage.

• Not eligible for most UK heat pump grants.

Best For

• Flats or compact homes with limited space for cylinders or pipework.

• Households wanting both heating and cooling functionality.

• Properties where hot water is supplied by a separate system.

4. High-Temperature vs Low-Temperature Heat Pumps

Low-Temperature Heat Pumps

These systems run at 35–55°C and offer the highest efficiency levels.

Suitable For

• Homes with underfloor heating, which operates best at low flow temperatures.

• Properties that have good insulation or have been recently refurbished.

• Households willing to upgrade to larger radiators for optimum performance.

High-Temperature Heat Pumps

These units can deliver 60–80°C, similar to traditional boilers.

Advantages

• Work with existing smaller radiators, reducing refurbishment costs.

• Suitable for older homes with thicker walls or limited insulation upgrades.

• Provide a comfortable heating experience without major system changes.

Considerations

• Higher running costs due to increased energy consumption at high flow temperatures.

• Efficiency drops compared with low-temperature systems.

5. Which Type Is Best for UK Homes?

For most UK households:

Monobloc air-to-water heat pumps strike the best balance between cost, simplicity and performance.

For colder regions or homes seeking premium efficiency:

Split-system air-to-water heat pumps offer improved winter performance.

For homes wanting cooling or with no space for a hot water cylinder:

Air-to-air heat pumps provide versatile heating and cooling (but not hot water).

For older Victorian, stone-built or poorly insulated properties:

High-temperature heat pumps allow compatibility with existing radiators and less disruption.

The vast majority of UK installations use air-to-water heat pumps, with monobloc systems being the most widespread due to their simplicity and cost-effectiveness. However, the “right” heat pump depends on your property layout, insulation levels, heating needs and available space.

A professional heat loss calculation is essential to determine the correct type and size, ensuring your system performs efficiently and reliably throughout the year. Contact Newpower today to enquire about air source heat pump Installation.