Types of Heat Pumps

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Heat pumps are changing the way we keep our homes warm and heat water. They are a great alternative to fossil fuel heating and can help lower energy bills by hundreds of pounds a year, while also helping combat climate change. Plus grants are widely available that help significantly cut installation costs, making them a much more affordable option for many households.

Heat pumps harness ambient heat from natural sources – the air, ground, or water. Each system works differently and has its advantages and disadvantages. This post explains how the different types of heat pumps work and explores the pros and cons, savings, and costs.

How Do Heat Pumps Work?

Heat pumps heat homes in cold weather by extracting heat from the air, ground, or water around a property and transferring it inside. In summer, they can help keep homes cooler by moving hot air inside your home to the outside.

A heat pump effectively uses the same refrigeration technology as an air conditioner. But it has a valve that can reverse the cooling process, enabling it to heat your home as well.

Heat Pump Components

Heat pumps consist of an outdoor unit, installed on an external wall, on the ground, or on a roof, and an indoor unit with a control system.

A thermostat placed in a central location in the house measures the temperature and controls the heating or cooling process. This maintains a comfortable temperature in your home all year round.

Most types of heat pumps also require a hot water cylinder, so you’ll need to install one if you don’t have one already. 

Air Source Heat Pumps

Air source heat pumps are the most common type of heat pump found in the UK, with tens of thousands of installations already, and the rate of adoption steadily growing.

ASHP’s take heat from the air outside the home and transfer it inside. The process can be reversed to keep homes cooler in hot weather. 

Air source heat pumps come in the form of air-to-water or air-to-air systems.

  • Air-to-water heat pumps are the most commonly installed type of ASHP. They feed heat into the water in central heating and hot-water supply systems. A large surface area is needed to release the heat, such as large radiators or an underfloor heating system.
  • Air-to-air heat pumps work in a similar way to air-to-water heat pumps but don’t provide hot water. Instead, they blow heat into homes through fans and a warm-air circulation system. They can also provide cold air in summer.

The Air-to-Water Heat Pump Heating Process

  • Air-to-water heat pumps extract heat from the air surrounding your house and pass it through an external heat exchange system.
  • The thermal energy evaporates refrigerant liquid in the heat pump, converting it into gas.
  • The gas is compressed to increase its temperature and then passed over an internal heat exchange surface.
  • Heat from the gas transfers to surrounding water and air. 
  • The heated air and water circulate around the home, feeding into a central heating system to provide heat and hot water.
  • As heat is transferred into the home, the gas in the heat pump cools, reverting to its original liquid state.
  • The cycle of reverse refrigeration is then repeated.

The Air Source Heat Pump Cooling Process

Air source heat pumps that incorporate a home cooling capability reverse the heating process. Chilled water is pumped through a convector fan coil unit that draws warm air from inside the home. 

The cold water cools the air, which is then directed back out into the home, reducing its temperature. The heat pump still provides hot water because the cooling process works independently from the heating and hot water circuit.

If your heat pump is being used for underfloor heating, it can also pump cold water through the system. This cools rooms by absorbing heat from sunlight that warms the floor.

Pros and Cons of Air Source Heat Pumps

Air source heat pumps are highly efficient but heat output decreases when external temperatures are low, especially below zero.

They require little maintenance apart from annual servicing by a heating engineer, and can last 20 years.

The installation process is simpler than that for ground source heat pumps, so air source heat pumps are suitable for home heating upgrades as well as new-builds.

On the downside, air source heat pumps produce less heat than boilers. This means you need larger radiators and your home must be well insulated.

Some people assume that air source heat pumps are noisy but they’re no louder than a gas boiler or fridge freezer.

Air Source Heat Pump Savings

Switching to an air source heat pump can lower fuel bills by 10 to 40%, saving up to £340 a year compared with an old G-rated gas boiler.

Air source heat pumps also result in carbon savings. They use only one unit of electricity to generate three to four units of heat.

Air Source Heat Pump Costs

Air source heat pumps generally cost half as much as ground source heat pumps. 

Air-to-water heat pumps cost around £8,750 to £14,000, typically paying for themselves in five to 10 years. Air-to-air heat pumps cost £2,400 to £8,800, with potential payback in six to 12 years.

Ground Source Heat Pumps

Ground source heat pumps take heat from under the ground around a property and transfer it into the home. The system works because the ground absorbs energy from the sun, with the ground temperature remaining relatively stable throughout the year. In the UK, the temperature a few metres below ground is consistently around 8°C to 11°C. 

A network of pipe loops connects an underground heat exchanger to the heat pump. Diluted antifreeze pumped into the pipes is warmed by the temperature of the ground. 

The liquid is then turned into a gas that boils at a low temperature. The temperature of the gas increases as it’s fed into a compressor. A condenser then distributes the heat to radiators or underfloor heating and to the hot water supply.

Ground source heat pumps are on average 300 to 400% energy efficient. This means they generate three to four kilowatts (kWs) of heat for every kilowatt of electricity they use.

Pros and Cons of Ground Source Heat Pumps

Ground source heat pumps are expensive to install but can be highly efficient, providing consistent heat throughout the year. But the level of efficiency depends on the type of soil or bedrock where the system is installed, and the complex installation makes them more suitable for new-builds.

Ground source heat pumps are quieter than air source heat pumps, and running costs are low. Maintenance is minimal – the underground pipes should last 70 years. However, horizontal installations require a large area of land – around 400 square metres to heat a three-bedroom house.

Ground Source Heat Pump Savings

Switching from an old, non-condensing gas boiler to a ground source heat pump typically cuts fuel bills by £630 a year, releasing 4,500kg less carbon dioxide into the atmosphere.

Making the switch if you have a newer, condensing boiler can lower energy costs by £105 a year, with 3,000kg in CO2 savings.

Replacing electric storage heaters with a ground source heat pump can cut annual energy bills by £1,500 to £2,300, with 4,500kg to 5,000kg less carbon emissions.

Ground Source Heat Pump Costs

Ground source heat pump systems can be installed horizontally or vertically.

A horizontal installation, with piping laid one to two metres underground, typically costs £16,200 to £31,000.

A vertical installation entails drilling boreholes to a depth of 80 to 160 metres. This makes it more expensive – up to £50,000.

Water Source Heat Pumps

Water source heat pumps have been around since the 1940s. Instead of extracting heat from the air or ground, they draw heat from a nearby body of water. This could be a stream or river, pond or lake, sea water, or water under the ground in aquifers.

They work in one of two ways, pumping water from the source directly through the heat pump, or pumping refrigerant fluid through pipes laid in the body of water. 

Like other types of heat pumps, water source heat pumps can cool homes as well as heat them.

Pros and Cons of Water Source Heat Pumps

Water source heat pumps are more efficient than air source heat pumps and ground source heat pumps. Because heat flows better through water, they can achieve up to 600% energy efficiency.

Water source heat pumps are also consistent. In the UK, water temperatures are stable all year round, averaging 7°C to 12°C.

The obvious drawback of a water source heat pump is that you need to live near a sustainable source of water.

Installation can be fairly difficult but water source heat pump systems tend to be easier to install than ground source heat pumps.

However, specific environmental regulations apply to water source heat pump installation and a licence may be required.

Water Source Heat Pump Savings

Water source heat pumps generate fewer carbon emissions than more traditional heating systems. 

They also reduce energy bills by an average of 15%. This typically saves households up to £1,100 a year, with payback typically in five years.

However, according to the Energy Saving Trust a water source heat pump can save up to £2,000 a year.

Water Source Heat Pump Costs

Water source heat pumps typically cost less than air source heat pumps – around £6,000 to £11,000, with average payback in five years.

Those using refrigerant fluid need less maintenance and are at the lower end of the price scale.

Water source heat pumps last at least 15 years and upwards of 50 years with good maintenance.

Hybrid Heat Pump Types

Hybrid heat pumps provide a solution when a standard heat pump isn’t a practical option. A hybrid heat pump is a dual energy system that integrates a heat pump with a traditional gas boiler or furnace.

The system monitors external temperatures and automatically chooses the most energy-efficient option to keep your home warm and heat the water.

Hybrid heat pumps work well in homes with high heating demands and can ensure a comfortable indoor temperature even in very cold weather.

Heat Pump Grants

Various grants are available towards the cost of installing most types of heat pumps. These initiatives include:

  • The Boiler Upgrade Scheme. Under the government’s £450 million Boiler Upgrade Scheme (BUS), grants up to £7,500 are available in England and Wales towards installing an air source heat pump, ground source heat pump, or water source heat pump. Funding is confirmed until the end of March 2028.
  • Energy Company Obligation Scheme. The Energy Company Obligation Scheme (ECO4) offers financial aid to low-income households in England, Scotland, and Wales who install a green heating system such as an air source heat pump.

Other heat pump grants for households on low incomes include:

  • The Home Upgrade Grant (HUG) in England.
  • Warmer Homes Scotland.
  • The Nest scheme in Wales.

Zero VAT

In addition to grants, VAT on installing heat pumps will be zero rated until March 31, 2027, when it will revert to the reduced rate of five per cent.

Heat Pumps Vs Boilers

Home heating accounts for around 14%of UK carbon emissions, according to the Department for Energy Security and Net Zero (DESNZ). Gas boilers are the main culprit. 

Heat pumps do the same as boilers – provide hot water and heating – but the technology is very different. 

A heat pump runs on a small amount of electricity and is a contemporary, eco-friendly alternative to the traditional gas boiler. Instead of generating heat by burning fuel, it transfers thermal energy from one place to another.

While a new standard gas boiler is around 95% energy efficient, heat pumps are 300% to 500% efficient because most of the energy comes from a natural, renewable source.

Three-quarters of the energy heat pumps use is generated entirely by the surrounding environment, with the remaining 25% by the household electricity supply.

Heating Considerations

Boilers can quickly heat radiators to a high temperature. A heat pump produces heat more slowly and with a lower temperature. This means the radiators it feeds work more like a convector, so they need to be larger to heat the same space. 

But heat pumps are ideal to power underfloor heating, which runs at a lower temperature than standard radiators. So you may want to update your radiators and pipework or switch to underfloor heating when you install a heat pump, especially if you live in an older property. 

Bear in mind too that the gradual heat build-up that heat pumps produce works best in well-insulated homes.

Heat Pumps and Net Zero

Burning fossil fuels – coal, oil, and natural gas – releases carbon dioxide and other greenhouse gases that trap heat in our atmosphere. This drives climate change and global warming. 

A further problem is that energy generated from fossil fuels is likely to become increasingly expensive as reserves become even scarcer. Heat pumps on the other hand are a sustainable, low-carbon heating solution that not only cuts energy bills but also takes us a step nearer the UK 2050 net zero target.

A high percentage of energy used by heat pumps is renewable, so they play a crucial role in decarbonising heating systems.

Gas Boiler Ban

As well as supporting installation of heat pumps, the government’s push towards net zero includes phasing out gas boilers. After 2035, gas boilers will no longer be installed in new-build homes, which will have to incorporate a greener, alternative heating system such as a heat pump.

Is a Heat Pump Right for Your Home?

Hundreds of thousands of heat pumps have already been installed across the UK. According to a government-backed research initiative, heat pumps are suitable for homes of all types and sizes. This was the verdict of an Electrification of Heat project commissioned by the Department for Business, Energy and Industrial Strategy (BEIS).

The initiative successfully installed air source heat pumps, ground source heat pumps, or hybrid heat pumps in a range of properties. These included flats and terrace homes as well as detached and semi-detached houses.

Heat pumps work best in homes that are well insulated and have large radiators or underfloor heating. In most cases, you don’t need planning permission to install a heat pump.

Heat Pump Cost Reductions

If you’re concerned about the cost of installing a heat pump, keep in mind that grants are available that cut prices considerably for many of the heat pump types.With a heat pump grant, you can install an air source heat pump system in a small home from £3,500 (similar to the price of a new boiler). In a medium-sized house, the cost would be from £5,500, and in a large property from £6,900.

And it’s easy to check your eligibility for a heat pump grant.

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Ollie Creevy
Ollie has been writing content online about home improvements for over 3 years. With a real interest and in-depth knowledge of heat pumps and ECO home improvement measures you can use to save on your energy bills. Ollie also keeps up to date with all the Government grants available for you to take advantage of like ECO4 and the Boiler Upgrade Scheme.