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Why are heat pumps the hot topic at the moment and what are they?

You may have heard about them in the news, it’s come up in conversation with a friend, or perhaps you’ve asked a professional for advice on some home upgrades — and now you’re left wondering, what exactly is a heat pump?

Air-Source Heat Pumps [Links in images]

In this post I have put together a high level overview of the background that’s led to heat pumps being in the limelight and the types of heat pump technology that’s currently available in the UK market.

Heating our homes

Globally, we emit around 50 billion tonnes of greenhouse gases each year.

The latest assessment from global climate scientists has been released, and the top lines are that the effects of the climate crisis are coming harder and faster than expected.

This is the critical decade for securing a liveable, equitable and sustainable future

No single solution or act is going to save us or the planet from ecological disaster. A myriad of solutions will need to be implemented, and quickly. The transition towards sustainable living cannot be delayed.

In the UK, heating the buildings in which we live and work accounts for approximately 20% of our Greenhouse Gas (GHG) emissions — about 14% of which is attributed to domestic properties.

In 2019, the Committee on Climate Change and its Adaptation Committee, produced a phenomenal report that assesses whether the UK’s housing stock is adequately prepared for the challenges of climate change; both in terms of reducing emissions from UK homes and ensuring homes are adequately prepared for the impacts of climate change.

The Committee’s report says action is needed in the following five areas:

  1. Performance and compliance. The way new homes are built and existing homes retrofitted often falls short of stated design standards.
  2. Skills gap. The chopping and changing of UK Government policy has led to a skills gap in housing design, construction and in the installation of new technologies.
  3. Retrofitting existing homes. Ensuring existing homes are low-carbon and resilient to the changing climate is a major UK infrastructure priority, and must be supported as such by the Treasury.
  4. Building new homes. New homes should be built to be low-carbon, energy and water efficient, and climate resilient.
  5. Finance and funding. There are urgent funding gaps which must be addressed, including secure UK Government funding for low-carbon sources of heating beyond 2021, and better resources for local authorities.
UK housing: Fit for the future? [Feb 2019]

Throughout the report, heat pumps are referenced extensively — from a new build and retrofit (existing housing stock) perspective, it is imperative that we stop using boilers (high carbon) and move towards renewable heating solutions —the good news is that this technology is already available and is being utilised around the world

Read here about how Norway has revolutionised the way they heat their homes over the course of just 15 years!

Moving Forward (New Homes Vs Retrofit)

New homes in the UK won’t be connected to gas from 2025 (following the Future Homes Standards) — this will mean that the majoirty of new homes will be heated via heat pumps. Although other technology is available, due to the scale of what’s needed, heat pumps are the most likely option — hydrogen is also on the table but the technology is still being developed so this is a few years away from being viable.

Regarding retrofitting existing homes, Chancellor Rishi Sunak has announced that VAT will be scrapped for insulation, solar panels and heat pumps in the Spring Statement 2022.

“Most heat pumps are currently charged at 20% VAT for materials due to a European Court of Justice ruling that if the materials account for more than 60% of the total installed cost (which they typically do) then the materials will be 20% VAT rated and only the labour will be 5% VAT rated. So this change will make a massive difference to the economics of heat pumps.” — Matthew Aylott, BEIS.

On top of this, replacing the Renewable Heat Incentive (RHI), the Boiler Upgrade Scheme (BUS) will launch in spring 2022 to aid the decarbonisation of buildings. It is set to provide £5,000 as an upfront capital grants to support the installation of heat pumps in homes (and some non-domestic properties).

Running Cost

As heat pumps run on electricity and a boiler burns gas, the running cost comparison needs to take into account the unit costs of each fuel.

Electricity costs between 12p and 24p per kWh depending on which tariff you are on, and natural gas is between 3p and 5p.

As the cost of electricity and the cost of gas change, so will the calculation about whether or not it will be cheaper for you to switch your heating system. You also need to be sure that the system will indeed achieve the indicated efficiencies.

One thing is for sure though. The cost of energy will continue to rise and the gap between the cost of electricity and the cost of gas is sure to close.

At the moment the switch from gas to a heat pump may not make financial sense, but as the energy cost gap closes, the numbers will certainly become more favourable for heat pumps.

So, what is a heat pump?

Heat Pumps

In the UK market there are several manufacturers offering a range of different heat pump technology, so it’s worth exploring what’s available so that you can understand the terms and nomenclature that often cloud their websites.

It’s worth clarifying for the purpose of this article, I’m only going to focus on domestic heat pumps — and only those that provide space heating and domestic hot water.

Some offer only one or the other, some also offer cooling and some even provide ventilation — but for the purpose of the average reader I’m only going to discuss below the options that you’ll most likely come across when listening to the news or seeking advice on changing your own system.

NOTE: Heat Pumps need to be connected to a hot water tank (cylinder) — the 3 different types of heat pump all have their own configuration/ product options.

1. Exhaust-Air Heat Pump

An Exhaust Air Source Heat Pump (EAHP) is a system which absorbs heat from the waste air (or exhaust air) leaving a building. Heat is extracted from the exhaust air and is upgraded into useful heat energy for space heating and domestic hot water.

EAHP Example: NIBE

The EAHP sits within the property, has an all-in-one hot water cylinder and heat exchanger, meaning that no additional components/ products are required — keeping footprint at a minimum.

These products are great for apartments or small homes where (1) the heat load for the property is very low and (2) there is no external space to locate any units.

Only a few manufacturers in the UK currently offer this range of heat pump technology as the capacity of the unit is low and so the application is quite niche.

2. Air-Source Heat Pump

The air-source heat pump (ASHP) sits externally to the property, absorbing heat from the air and transferring it into the property.

ASHP Example: Daikin Monobloc

With ASHP there are 3 distinct offerings — which one you choose will be dependent upon your property requirements.


Single outdoor unit — water pipework connects to a water storage tank (cannot exceed 10m distance). No FGas qualifications are required so theoretically, a plumber can install this (though please check that as a minimum they’ve completed the relevant manufacturers’ basic product training course).

Up to ~50/55degC water temp for space heating. Good for new build and retrofit where the outdoor unit can be located close to the property.

Split heat pump (low temp)

Outdoor unit connected via refrigerant pipework to an indoor unit and water storage tank. Up to 30m distance can be achieved. FGas qualified engineer needed to install this due to refrigerant pipework*.

Up to ~55degC water temp for space heating. Good for new build and retrofit where the outdoor unit cannot be located close to the property i.e low-rise flats.

Split heat pump (high temp)

Outdoor unit connected via refrigerant pipework to an indoor unit and water storage tank. Sometimes up to 30m distance can be achieved although this would need to be clarified by the manufacturer. FGas qualified engineer needed to install this due to refrigerant pipework*.

Up to ~70degC water temp for space heating. Good for retrofit where minimal works can be carried out on the existing wet system.

*Some, split-heat pumps (low temp and high temp) work using a hydro-split technology rather than refrigerant-split. This potentially means that you won’t need an FGas qualified engineer to install the system but maximum pipework distances should still be confirmed by the manufacturer.


All 3 options have flexibility with cylinder selections, most manufacturers will advise that you stick to using their own cylinders as this will ensure you get the best package in terms of servicing and warranty — but providing you check compatibility, you can consider going down the 3rd party route.

  • Pre-plumbed cylinders- the plug ’n’ play market solution, most likely to be paid with the monobloc and in the new build sector. Pre-fitted with 20litre buffer vessel / hydraulic separator, G3 kit (expansion vessel supplied loose), wiring box, 3-way valve, on board pump, magnetic filter, automatic air vents, dual immersion heaters and thermostatic mixing valve
  • Unvented cylinders- most common type of tank on the market. Improved pressure and flow rate.
  • Integrated cylinders- similar to the EAHP in terms of aesthetics, an integrated cylinder is a real space saver for split-type air-source heat pumps, combining the indoor unit with the cylinder to save on footprint.
  • Smart cylinders- connected to the internet to measure and deliver energy saving with your hot water usage. See Mixergy.

3. Ground/ water-source heat pump

With Ground or water-source heat pumps, planning becomes key, there becomes a real opportunity to create and design in flexibility for large decarbonisation schemes and connection to heat networks.

Example WSHP (Left to right): Daikin, Vital Energi, Kensa.

Local/ Decentralised Approach

An individual heat pump located inside the property, often an integrated unit (heat pump and cylinder)— connects to a water loop (either via a borehole or slinky tube in ground). High upfront cost due to groundworks. Benefits from high performance to due to steady ground/ water temperature.

Good for new build or retrofit where land is available.

Centralised Appoach

Water-source heat pump per apartment/ home — all connected to a shared/ common water loop that feeds the whole building.

Ideal for high rise apartments or new build towns with a heat network.

Heat injection to the common water loop for this approach can be via a district heating network, a commercial (large) air-source heat pump, ground source or even surface water.

Focus of this article is on the domestic heat pump approach, future posts will look into full building design and consideration for networks (heat networks and smart grids).

Making a decision

Whether a heat pump is right for you will be dependent upon several factors such as whether or not you own the property you currently live in (or at least have the right to retrofit) and your own financial circumstances (this is no easy/ cheap decision).

If you are fortunate enough to be in the position to start looking into getting a heat pump, then please take your time and ensure you spend your money wisely.

As mentioned before, when focusing on the Climate Crisis there is no single solution — heat pumps (as much as I love them) will not save the world (at least not on their own).

Before we get into saving the planet (eat less meat, use your vote with the planet in mind, invest your pensions ethically (into ESG funds) etc) — focusing on the energy efficiency of your home is a must.

We absolutely must stop using fossil fuels, and heat pumps will help us achieve this — but we also need to reduce our energy consumption.

Get a smart meter. Reduce your energy usage. Reduce your energy (heat) requirement — improve your home insulation and fabric performance.

I hope you’ve enjoyed this post- if you do have any further questions or comments about heat pump technology please do reach out!



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