Heat Pumps

Heat pumps do not look like a hugely sexy technology, but what they do is pretty magical. Technologically, they are just fridges in reverse. They move outside heat – either from the air or from the ground – into your house.

The way they work makes them hugely efficient, which is why they are being viewed by so many as the key to decarbonising the UK’s heating.

Heat pumps are still rare in the UK, only about 30,000 were installed last year compared to about 1.5 million gas boilers. But internationally they are widely used. In Sweden and Switzerland they account for about a third of heating system sales.

The UK government has just announced that it intends to try to reach 600,000 heat pump sales per year by 2028, a twenty-fold increase.  It hopes that there will be 5.5 million heat pumps installed in homes by 2030, of which 2.2 million will have been installed in new homes, and the rest retrofits.

Heat pump performance

Heat pumps have had a mixed reception in the UK.

Trials conducted between 2008 and 2013 initially showed that they were performing very poorly, much less efficiently than in other European countries. But in the second phase of the trial, once specification and installation were improved, they improved markedly.

Efficiency seems to have been improving further since, and there are more trials ongoing now.

Where they are specified and installed well, satisfaction levels seem to be high – around 80% of people say that they are happy with their pump.

Cost and running costs of heat pumps

For many people heat pumps probably don’t fall into the ‘win-win, save money and save the climate’ bracket. We cover cost in more detail below, and also see our feature on heating and energy grants.

However, there are UK properties for which they are much more financially attractive, particularly the 14% which are not connected to the gas grid. And if you’ve already insulated your house, getting one is a major step you can take to help the climate.

The biggest problem with heat pumps is the cost. The upfront costs are quite high, and if you’re comparing one against a modern efficient gas boiler, you sadly may not save money on running costs.

Electricity is currently about 3 or 4 times the cost of gas. So although heat pumps are about 3 or 4 times more efficient, these cancel out and you could expect your running costs to be about the same.

• The Climate Change Committee estimates the average cost of an air-towater heat pump + installation at £6,415, and ground source at £13,380, with up to £3,500 additionally required to make house changes such as increasing radiator size. Installation prices can, however, vary a lot. The Energy Saving Trust estimates an efficient gas boiler replacement to be about £2,300.
   
• A hybrid system can be cheaper if you already have a boiler and are just installing a heat pump to work alongside it, because you may get away with a lower capacity heat pump and without replacing your radiators. Costs vary, but one report suggested that it could be around 30% less than a full heat pump system.
   
• There’s less information available about air-to-air heat pumps. On their face they look significantly cheaper, but you would need something else for hot water, and additionally you may need more than one. Those factors may well counteract the savings.

The Climate Change Committee estimates that the price of the pump and installation may fall by about 23% over the next fifteen years, if – as it recommends – the UK becomes such a large heat pump market that there start to be efficiencies of scale involved.

Different types of heat pump and what do you need to install a heat pump

Installing a heat pump is likely to require other changes to your house. Firstly, they do produce less heat, so the house needs to be well insulated.

Secondly, most heat pumps are at their most efficient when they heat radiator water to 35-45 degrees, as opposed to the 65-80 degrees normal with gas boilers.

This means that you may need larger surfaces like large radiators or underfloor heating, and to increase the size of your hot water tank.

There are some ‘high temperature heat pumps’, which are optimised to heat to a higher temperature so they can be used with standard-sized radiators. But they are less efficient, the external units are much larger, and the pumps are 20-35% more expensive than standard ones.

Installation involves drilling holes through the walls, which may require planning permission.

Type 1 air source heat pumps: air to water

Most of the heat pumps installed in the UK are air to water. They do both space and water heating.

They can be installed on almost all properties, including flats. A normal pump is about the size of a fridge, and you just need a place outside where it can be fitted to a wall or placed on the ground, with space around it to get a good flow of air.

All air source heat pumps do produce some noise, as they contain a fan, but the modern ones are much quieter – about 40 to 60 decibels, which is rarely a problem.

Type 2 air source heat pumps: air to air

Air to air heat pumps are just air conditioners that have been put into reverse. They blow hot air into your house, so they only do space heating. You will need something else for hot water.

However, air to air pumps do have some advantages. The pumps are cheaper and have good efficiency. Since they don’t use radiators, you won’t need to install bigger ones, although you may need ducting (pipes) in order to carry the hot air around to different rooms.

Ground source heat pumps

Ground source heat pumps (see graphic right) take heat from the ground instead of the air, using pipes buried outside the house. This makes them much more efficient, and silent, but they are more expensive and only suitable for a limited number of properties due to the outside space requirements.

In the case of the horizontal ones, pipes are buried in your garden in a long trench about a metre deep – you will need an area about twice the size of your house.

The vertical ones have the pipes in a series of boreholes instead, so they require much less space. But they are more expensive to install and you will still need space for the drilling machinery – they go down around 70 to 100 metres.
 

Hybrid heat pumps

Hybrid systems combine a heat pump and a traditional boiler. The theory is that the heat pump does most of the work, but the boiler helps out in particularly cold weather, when heat pumps struggle.

Hybrids have some advantages, and many complete decarbonisation scenarios incorporate some as a way of reducing peak electricity demand.

Nibe Electricity is quite difficult and expensive to store in large amounts, so huge peaks – like on very cold winter evenings, when everyone turns their heating up to max – are a problem.

The Climate Change Committee’s 2019 total decarbonisation scenario has a quarter of the homes that run on heat pumps in 2050 using a hybrid system, with the boiler part using hydrogen, or bioenergy in the case of homes off the gas grid.
 

Gas fired and water-source heat pumps

You can get gas-fired heat pumps. They do use less gas than boilers, but most people seem to be suggesting that they aren’t hugely cheaper than the electric ones, so there doesn’t seem to be any compelling reason to get one when it is better to get off gas altogether.

You also get water-source heat pumps, but they are rarely used at domestic level.

Installation

You should make sure that your installer is accredited by a Microgeneration Certification Scheme (MCS)-appointed certification body. It is a good sign if they are also registered with other organisations and bodies, such as the Renewable Energy Assurance Ltd (REAL) and the Ground Source Heat Pump Association, which encourage high installation standards.

Heat pump efficiency and environmental impact

The main measure of a heat pump’s efficiency is called the coefficient of performance (COP). It measures how many units of heat you get out per unit of energy you put in.

A 100% efficient direct electric heater, which does no heat pump magic, has a COP of one. A 90% efficient gas boiler has a COP of 0.9.

Standard ground source heat pumps average COPs of around four, and air source about three.

However, the COP varies depending on the weather. So, when you’re comparing individual pumps you want to look at the average COPs they manage over a heating season. This is either given as the Seasonal Coefficient of Performance (SCOP) or the Seasonal Performance Factor (SPF).
 

Carbon footprint savings from heat pumps

As the grid decarbonises over your heat pump’s lifetime, emissions will fall towards zero. But even now, the annual carbon savings are good.

The current carbon footprint of a unit of UK electricity is on average about 1.3 times that of natural gas. You can do a rough estimate of the emissions savings you can get from heat pumps from this and their SCOP – if it is three, emissions would be less than half of those from the most efficient gas boiler.

Estimates of immediate emission cuts from studies are around 70% for standard heat pumps, 50-60% for high temperature heat pumps, between 18 and 55% for hybrid systems (it depends on the set up and how you use them), and about 20% for gas-fired heat pumps.

To put it in absolute figures, the Energy Savings Trust estimates that air source heat pumps save more than two tonnes of CO 2e per year on the most efficient gas boilers, right now. The average UK carbon footprint per person, including all imported goods, is about twelve.

Energy labels for heat pumps

All heat pumps have energy labels. Although they may be changing now we have left the EU, the familiar ErP label is still being used.

The same scale is used for all heating technologies, meaning that heat pumps by definition fall into the top three classes: A+, A++ or A+++. The rating is based on the SCOP.

When heat pumps are required to deliver a hotter output their efficiency drops. Heat pumps have two ratings for space heating, for low temperature delivery at 35°C, and medium temperature delivery at 55°C.

There are several other numbers on the label as well, including a decibel noise rating, and a hot water rating if they produce hot water, although heat pumps are normally all in Class A for that. To achieve higher efficiency, they need to be combined with solar heating.

The quantity of hot water will also be illustrated by a tap symbol indicating sizes (tap profiles) from 3XS to XXL.

Refrigerants in heat pumps

Heat pumps use refrigerants, and the most common traditionally has been a hydrofluorocarbon (HFC) called R410A, which has a Global Warming Potential (GWP) of 2088, meaning that it has 2088 times the warming effect of CO2.

Although it should be possible to recover the refrigerant at the end of life, there may be some leakage.

R410A is now being phased out under EU F-Gas regulation. Some heat pump manufacturers, such as Mitsubishi, are moving to another HFC called R32, which has a GWP of 675, although that too is going to start being phased out soon.

Others such as Vaillant are switching to propane, which has a GWP of 3, or to ammonia or CO2.

But some of these have their own problems, such as being unacceptably toxic or significantly less efficient, meaning that more electricity is used. And while the grid is still half based on fossil fuels, this can result in a higher carbon footprint than the ones with high GWPs (although once the grid is fully decarbonised, we won’t need to worry about that).

According to the Climate Change Committee: “if existing standards are maintained, the greenhouse gas savings of a switch to heat pumps are orders of magnitude higher than the additional F-gas [HFC] emissions.”

Given the complexity and that the climate impact is small, we decided not to rate companies on the basis of the refrigerants they use in their heat pumps.

Manufacturers of Heat Pumps

We found ethical issues around both carbon reporting and tax avoidance. 

Despite manufacturing this emissions reduction technology, only a handful of companies scored well in our ranking of carbon management and reporting for their own operations. Our criteria require, amongst other things, reporting annually on emissions and setting targets for reductions in line with international agreements. This ranking appears in the Climate Change column. The worst were Bosch (Worcester), Glen Dimplex, Grant Engineering (Grant), Viessmann
 

Most companies in this guide received our worst rating for likely use of tax avoidance strategies. The exceptions were Kensa, Danfoss, Nu-Heat, Vaillant (including Glow-worm), and Grant Engineering (Grant), which all received a best, and Mitsubishi Electric, which received a middle rating. Kensa and Mitsubishi’s scores were however brought down by other parts of their company structures.

Which company makes what kind of heat pump?