Pump up the jam

Heat pumps are playing an increasingly important role in both new build and retrofit sectors – Charlotte Lee, Chief Executive of the Heat Pump Association (HPA), demystifies a few things.

The basic technology involves a refrigerant compression cycle. A heat pump uses a refrigerant gas to gather low-grade heat from either the air, ground or water, and runs that through a compression cycle to increase the temperature in a way that can then be utilised within a building. By using the low-grade heat to start and then a refrigerant compression cycle, heat pumps are extremely efficient – it is common to hear of efficiencies above 300%.

How can anything be 300% efficient?

For every unit of electricity the heat pump uses to generate heat, it can turn that unit of electricity into three or four units of heat. A recent Electrification of Heat Demonstration Project by the UK government saw air-to-water heat pumps with an average efficiency of 290%, although some work at more than 500% efficiency.

The efficiency of the heat pump will depend on a number of factors, including system design, installation and customer behaviour. Heat pumps are typically less tolerant to heating systems designed to operate at high temperatures than a fossil fuel boiler would be, because they often are not designed to reach those high temperatures. That is why it is really important to get the design and the installation of the system right – alongside the correct customer handover.

Heat pump myths debunked

Myth 1: Heat pumps only work in highly insulated properties

A heat pump could heat a barn with the doors open – it just would not do it very efficiently (no heating system would). It is always optimal to ensure that the building has cost-effective energy efficiency measures in place, such as draft-proofing, loft insulation and cavity wall insulation if suitable. But the heat pump will be sized according to the property’s need and will still heat the property regardless of the heat loss.

Myth 2: Heat pumps do not work in the cold

Our friends over in Norway and northern Europe, where there is a proliferation of heat pumps installed, would laugh at this idea. Heat pumps work in cold climates – the refrigerant gases that are often used in the UK can extract heat from air down to -20°C. They will run defrost cycles and they will be slightly less efficient at very cold temperatures, but they will still work and can extract low-grade heat from minus temperatures.

Myth 3: Heat pumps are noisy

With ground-source heat pumps, there is no noise. With outdoor air-to-water and air-to-air units, any limited noise comes from the compression system and the fan speed from the outdoor unit. New heat pumps on the market are extremely quiet because of enhanced design. In order to meet permitted development rights, they need to comply with the MCS 020 Planning Standard, which means they must meet strict noise criteria.

Myth 4: You need lots of space

This is really a mixed answer. Indoors, if you already have a hot water cylinder, the additional space needed should not be prohibitive. However, if you are installing a heat pump to replace a combi boiler, you will need to find some extra space for the hot water solution – perhaps an expansion tank or a buffer vessel and an indoor unit. Outdoors, the air-to-water units are usually smaller than 0.6m3 because that is what is required to have permitted development rights.

How easy is it to find competent design and installation providers?

The key is to use an organisation certified to the Microgeneration Certification Scheme (MCS), which UK governments require for access to grant schemes. MCS sets the design and installation standards for heat pumps.

There is a split within MCS that allows organisations to be certified just for design and/or installation. So, a certified design business could undertake the indemnified design for the property, and then a separate business would do the installation however, businesses are mainly certified to do both.

How many installers are there in the UK?

There is no shortage in people successfully completing heat pump training: 2024 figures showed that more than 9,000 people successfully completed a recognised heat pump training course. That is a 15% increase on 2023 figures, and between 2022 to 2023 the HPA saw an 133% increase. There is also a new low-carbon heating technician apprenticeship that has been launched this year that is being run by a number of colleges.

In addition, the government in Westminster has committed to introducing mandatory low-temperature heating system training for all fossil fuel boiler engineers. This is to ensure that they are familiar with the importance of low-temperature heating design, which will support the roll-out of heat pumps.

What is the sequence of measures involved in the installation?

In order to access government grants, such as the Boiler Upgrade Scheme and Energy Company Obligation, a householder would need to have a valid (less than ten years old) EPC.

A heat loss calculation would then be carried out at the property, which would analyse if any emitter upgrades were needed to optimise the efficiency of the heat pump. Heat pumps, in most cases, operate at lower than 55°C flow temperature, which is why you might need some emitters with a larger surface area (such as larger radiators) in the property.

If you were accessing a grant in England and Wales, the installer would then apply to the Boiler Upgrade Scheme on your behalf to get the £7,500 towards your heat pump installation. In Scotland, the homeowner would apply for the Home Energy Scotland scheme and receive £7,500-£9,000. The installer would also need to complete a ‘connect and notify application’, or a request to connect application to the local distribution network operator for a grid connection – that can be done via an online app called Connect Direct, which will advise if the installation can go ahead or if upgrade works are needed. An assessment on whether planning permission would be required needs to be undertaken too.

Finally, energy efficiency upgrades may be needed, such as new radiators or underfloor heating pipe upgrades and possibly cost-effective insulation measures. Then the heat pump and typically a new hot water cylinder would be installed.

Are there any legislative changes in the offing?

Permitted development rights for air-to-water heat pumps do exist but the HPA has had an announcement that they are changing. The HPA does not know exactly when those changes will occur, but has been told it will be in the spring.

After that, it will be much easier to install air-to-water heat pumps under permitted development rights because the changes will remove the 1m boundary rule; the size limit of the heat pump unit will be increased from 0.6m3 to 1.5m3; and it will become possible to use two heat pumps for large, detached dwellings without requiring planning.

There will also be changes to support the installation of air-to-air heat pumps – currently you require planning permission to install air-to-air units, but you won’t need that when these changes come in.

Heat pump types explained

Air-to-water heat pumps

Air-to-water heat pumps are either split systems or monobloc units and different qualification and training requirements apply to both.

Air-to-water monobloc units are currently the most common heat pumps in the UK, with 78,000 monobloc air-to-water heat pumps sold in 2024.

Air-to-water heat pumps extract energy from the air and use the refrigerant compression cycle to increase the temperature of this low-grade heat to a level that can be used to heat the heating system and the domestic hot water of a property.

Ground- or water-source heat pumps

Ground- or water-source heat pumps extract energy from the ground, either via a bore hole up to 200m deep, or via a horizontal array around 1.5m below the ground. The bore holes are used where space is restricted but they are more expensive; the horizontal arrays are cheaper but require a much bigger area.

The benefit of the heat from the ground is that it stays at a much more consistent temperature than air temperature. These heat pumps also often operate at higher efficiency, but the initial cost for the groundwork is higher.

Air-to-air heat pumps

Air-to-air heat pumps are effectively air conditioning units that offer both heating and cooling; there are not any currently on the UK market that only offer heating. Whereas air-to-water and ground-to-water heat pumps use a typical water-based central heating system of pipes and radiators or underfloor heating, air-to-air extract heat from outside and blow hot air into the building.

Air-to-air heat pumps are more suited to smaller properties and properties that do not have a wet central heating system installed. They offer much higher efficiencies compared to direct electric heating systems – although they are not quite as efficient as water-based systems. That means they currently do not benefit from support under the Boiler Upgrade Scheme or government grants, but work is being done to update the relevant certifications for installers and product standards to enable them to access some of the government-funded schemes.

Because they are most suited to flats and smaller dwellings, there are challenges associated with the visual impact of having multiple outdoor units on a block of flats. They also do not offer a solution for domestic hot water provision.

Domestic hot water heat pumps

Domestic hot water heat pumps extract heat via a ducted system from the air outside. However, they do not require a big outdoor unit, just a vent in the side of the house. The heat extracted from the air outside is taken back to a mini heat pump that sits within the hot water cylinder and heats the water within the cylinder. It does this much more efficiently than an immersion heater or a direct electric solution.

Because only a vent is required, these systems do not require planning permission.

Hybrid heat pumps/hybrid heating systems

There are different options when it comes to hybrid heat pump systems, although the key component is there must be a single master controller. One option is a single unit that contains both a fossil fuel boiler plus a heat pump; another option is a packaged hybrid – a separate boiler and heat pump but sold together with a single master controller; and the third option is an existing boiler in a property with a heat pump added to it.

Currently, while there is 0.5 of a credit under the Clean Heat Market Mechanism if you install a heat pump as part of a hybrid heating system, you do not get government funding for it under the Boiler Upgrade Scheme – although you can in some instances via the Energy Company Obligation. This mixed situation is a reflection of the challenge in quantifying the benefit these systems bring in terms of carbon savings, and also concerns around the maintenance, service and upfront costs of having two units rather than one.

Exhaust air heat pump

An exhaust air heat pump transfers heat from an internal ventilation system to water, which is then used to heat properties and domestic hot water, normally via a wet central heating system.

What other areas of guidance might be important to CABE members?

The HPA will be publishing a guidance document to support installers to select an appropriate residual current device for a heat pump installation.

Also, with the increasing regulatory pressure to reduce the quantity of fluorinated refrigerants placed onto the market, equipment manufacturers are seeking to use lower Global Warming Potential (GWP)refrigerants in their heat pump technologies. Typically, these are non-fluorinated and not covered by the current F gas regulations. Many of the lower GWP refrigerants have a safety class rating of ‘flammable’ or ‘higher flammability’. There is currently no minimum or mandatory training and handling requirement for engineers working on the refrigerant circuit of a heat pump, and no requirement to hold a ‘flammable refrigerants’ handling qualification. It should be noted that the Health and Safety at Work Act obliges companies to consider risks and safe working practices.

The HPA recommends that awareness of both F gas and non-F gas flammable refrigerants should be held by all those installing heat pumps, and an overview of such must be included in all heat pump training courses. For those installers who are installing split-refrigerant heat pump systems containing a non-F gas flammable refrigerant and those who break the hermetic seal of a heat pump containing a non-F gas flammable refrigerant for servicing/maintenance purposes, the HPA recommends that they should hold a formal Flammables Refrigerant Handling qualification that aligns with the ACRIB specification.

See more information: heatpumps.org.uk
The Microgeneration Certification Scheme has a searchable list on its website for certified businesses: mcscertified.com/find-an-installer

Image credit | iStock