Air to Air Heat Pumps UK: How They Differ

Published: March 2026 | Reading time: 9 minutes

When most people in the UK talk about heat pumps, they mean air-to-water systems — the kind that connects to your radiators and hot water cylinder. But there's another type that's worth knowing about: the air-to-air heat pump.

Air-to-air heat pumps are essentially reversible air conditioning systems. They're cheaper to buy, simpler to install, and can both heat and cool your home. But they can't provide hot water, and they don't qualify for the Boiler Upgrade Scheme grant. So when does an air-to-air system make sense?

This guide explains how air-to-air heat pumps work, how they compare to the more common air-to-water systems, and when you might want to choose one.

How Air-to-Air Heat Pumps Work

An air-to-air heat pump works on the same fundamental principle as an air-to-water system: it uses a refrigerant cycle to extract heat from outdoor air and move it indoors. The difference is in how that heat is delivered to your rooms.

• Air-to-water: Transfers heat to water, which is then circulated through radiators or underfloor heating. Can also heat a hot water cylinder.
• Air-to-air: Transfers heat directly to the air inside your rooms via wall-mounted, ceiling-mounted, or ducted indoor units. Think of a modern air conditioning system that can also heat.

Each room (or zone) that you want to heat needs its own indoor unit, connected by refrigerant pipes to the outdoor unit. A single outdoor unit can typically serve 2-5 indoor units (this is called a "multi-split" system).

Heating and Cooling

One significant advantage of air-to-air systems is that they can reverse direction — heating in winter and cooling in summer. With UK summers getting warmer and heatwaves becoming more frequent, this dual capability is increasingly attractive.

Air-to-water heat pumps can technically provide cooling too, but it requires specific setup (fan coil units or cooling-capable underfloor heating) and is much less common in the UK.

Air-to-Air vs Air-to-Water: Key Differences

Costs: Air-to-Air Heat Pumps

Air-to-air systems are considerably cheaper to buy and install than air-to-water systems:

Purchase and Installation Costs

• Single room (one indoor unit): £1,200 – £2,500 installed
• 2-3 rooms (multi-split): £3,000 – £5,500 installed
• Whole house (4-5 rooms): £5,000 – £8,000 installed

These figures include the outdoor unit, indoor units, refrigerant pipework, electrical connections, and labour.

Running Costs

Air-to-air systems are typically more efficient than air-to-water for space heating alone, with SCOP ratings of 3.5-5.0. This means lower electricity consumption per unit of heat delivered. However, you'll still need a separate system for hot water (immersion heater, electric boiler, or gas system), which adds to the overall energy cost.

The Grant Issue

The biggest financial drawback: air-to-air heat pumps do not qualify for the Boiler Upgrade Scheme (BUS) grant of £7,500. This is because they don't provide hot water and are classified as air conditioning rather than heating systems under current UK regulations.

When you factor in the grant, the cost comparison changes significantly:

• Air-to-air (whole house): £5,000 – £8,000 (no grant available)
• Air-to-water (whole house): £8,000 – £15,000 minus £7,500 grant = £500 – £7,500

After the grant, an air-to-water system can actually be cheaper than air-to-air for many homes.

Pros of Air-to-Air Heat Pumps

1. Lower Upfront Cost (Before Grants)

If you can't access the BUS grant (perhaps because you don't have a fossil fuel boiler to replace, or you've already claimed it), air-to-air is significantly cheaper to install.

2. Cooling in Summer

This is the standout advantage. With UK heatwaves becoming more frequent and intense, built-in cooling is a genuine benefit. An air-to-air system can cool your home to a comfortable temperature when outdoor temperatures hit 30°C+.

3. Quick Response Time

Air-to-air systems heat a room much faster than radiators or underfloor heating. If you need warmth quickly in a specific room, an air-to-air unit delivers almost immediately.

4. Easy Room-by-Room Control

Each indoor unit operates independently with its own thermostat and timer. You can heat only the rooms you're using, which can be very efficient in larger homes where not all rooms are occupied.

5. Minimal Disruption to Install

Installation involves mounting indoor units on walls, running refrigerant pipes (usually through small holes in external walls), and connecting the outdoor unit. There's no need to modify your existing plumbing, change radiators, or install a hot water cylinder.

6. Higher Efficiency for Space Heating

Because air-to-air systems deliver heat at lower temperatures (warm air at 25-35°C rather than hot water at 40-55°C), they typically achieve higher COP/SCOP ratings for space heating alone.

Cons of Air-to-Air Heat Pumps

1. No Hot Water

This is the biggest limitation. Air-to-air systems cannot heat your domestic hot water. You'll need a separate solution — typically an immersion heater in an existing cylinder, an electric point-of-use heater, or a retained gas boiler for hot water only. This adds complexity and potentially reduces overall energy savings.

2. No BUS Grant

Missing out on £7,500 is significant. For many homeowners, the grant makes air-to-water systems the more affordable option overall.

3. Indoor Units in Every Room

Each heated room needs a wall-mounted or ceiling-mounted unit. Some people find these visually intrusive — they look like air conditioning units (because that's essentially what they are). This is a matter of personal taste, but it's quite different from the invisible heating provided by radiators or underfloor heating.

4. Fan Noise Indoors

The indoor units have fans that produce a gentle but audible whooshing sound. On the lowest settings, this is typically 20-25 dB (barely noticeable), but on higher settings it can reach 35-45 dB. Some people find this intrusive, particularly in bedrooms at night.

5. Moving Air Can Feel Draughty

Warm air blowing across a room feels different from the radiant heat of radiators or underfloor heating. Some people love the quick warmth; others find the air movement uncomfortable or drying. Modern units have wide-angle louvres and "comfort" modes that minimise this, but it's a different heating experience.

6. Less Even Heat Distribution

Warm air tends to rise and can create temperature stratification — warmer near the ceiling, cooler at floor level. Radiators and particularly underfloor heating provide more even warmth throughout a room.

When Does Air-to-Air Make Sense?

Air-to-air heat pumps are the right choice in specific situations:

Best Suited For:

• Properties without wet heating systems: If your home uses electric panel heaters, storage heaters, or electric underfloor heating, an air-to-air system can replace these without needing to install an entire wet heating system (radiators, pipes, cylinder).
• Supplementary heating: Adding warmth to specific rooms — a home office, a conservatory, an extension — where running radiator pipework would be impractical or expensive.
• Properties where cooling is a priority: South-facing flats, top-floor apartments, or homes that overheat in summer. The dual heating/cooling capability is a strong advantage.
• Rental properties and landlords: Quick, low-disruption installation makes air-to-air practical for rented properties where extensive plumbing work isn't feasible.
• Budget-conscious homeowners: If the BUS grant isn't available to you and upfront cost is the primary concern.
• Holiday homes and second properties: Where quick heat-up time is more important than constant background warmth.

Less Suited For:

• Replacing a gas boiler: You'd be better with an air-to-water system that handles both heating and hot water, especially with the £7,500 grant available.
• Homes with existing radiators in good condition: An air-to-water system connects to your existing wet heating system with minimal changes.
• Households prioritising aesthetics: If you don't want visible indoor units in every room.

For a comprehensive look at the more common alternative, see our air-to-water heat pump guide.

Installation: What to Expect

Air-to-air installation is simpler and quicker than air-to-water:

• Timeline: 1-2 days for a typical 3-room installation, compared to 2-5 days for air-to-water.
• Outdoor unit: Mounted on a wall bracket or ground stand, similar to an air-to-water system but typically smaller.
• Indoor units: Wall-mounted high on the wall in each room (usually near the ceiling). Ceiling cassette and ducted options are also available but cost more.
• Pipework: Copper refrigerant pipes run between the outdoor and indoor units, usually through small (65-70mm) holes in external walls. These can be concealed in trunking or channelled into walls.
• Electrical: The system needs a dedicated electrical circuit from your consumer unit.
• Planning permission: Not usually required under permitted development, but check local rules and conservation area restrictions.

Brands Available in the UK

Major air-to-air heat pump brands available in the UK include:

• Daikin: Wide range of split and multi-split systems, excellent efficiency ratings
• Mitsubishi Electric: Popular for both residential and commercial, very reliable
• Samsung: Competitive pricing, good smart features and app control
• LG: Strong range with stylish indoor units and good energy ratings
• Panasonic: Well-regarded for quality and quiet operation
• Fujitsu: Reliable with good cold-climate performance

Ensure your installer is F-Gas registered and experienced with heat pump installations, not just standard air conditioning work.

Frequently Asked Questions

Can an air-to-air heat pump heat my whole house?

Yes, if you install indoor units in each room that needs heating. A multi-split system with one outdoor unit can serve 4-5 rooms. For larger homes, you may need two outdoor units. However, hallways, landings, and rooms without units won't receive direct heat — they'll rely on indirect warmth from adjacent heated rooms.

Are air-to-air heat pumps eligible for the BUS grant?

No. The Boiler Upgrade Scheme grant (currently £7,500) is only available for air-to-water and ground source heat pumps that provide space heating and hot water. Air-to-air systems are excluded.

Can I use an air-to-air heat pump alongside my existing boiler?

Yes. Some homeowners use air-to-air heat pumps as the primary heating system while retaining a gas boiler solely for hot water. Others use air-to-air units to supplement existing heating in specific rooms. Both approaches work.

How much does it cost to run an air-to-air heat pump?

For a typical 3-bed house, annual heating costs with an air-to-air system are around £400-700 for space heating. You'll need to add the cost of hot water heating separately (typically £200-400/year with an immersion heater). Total energy costs are usually lower than gas heating but the margin is tighter than with an air-to-water system because of the separate hot water requirement.

Are air-to-air heat pumps noisy indoors?

Modern indoor units operate at 19-25 dB on the lowest fan speed — barely audible in most situations. On higher speeds, noise can reach 35-45 dB. Night modes reduce fan speed and noise for sleeping. Most people adapt quickly and stop noticing the sound.

Do air-to-air heat pumps need planning permission?

Usually not, as they typically fall under permitted development rights. However, there are conditions around noise levels and, in conservation areas or listed buildings, you may need to apply. Check with your local planning authority if in doubt.

The Bottom Line

Air-to-air heat pumps are a viable heating option for UK homes, particularly where cooling is also valued, where there's no existing wet heating system, or where budget (without grant access) is the primary concern. They're cheaper, simpler, and more efficient for space heating alone.

However, for most UK homeowners replacing a gas boiler, an air-to-water heat pump remains the better all-round choice — especially with the £7,500 BUS grant. It handles both heating and hot water, works with your existing radiators, and integrates seamlessly as a complete replacement for your boiler.

Not sure which type suits your property? Use our heat pump suitability checker to get a recommendation, or request free quotes from MCS-certified installers who can advise on the best system for your home.