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Essential guide to heat pumps in 2023

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Heat pumps are the primary method for decarbonising domestic space and water heating and are a key technology for helping achieve net zero emissions from domestic heating. The UK Government has announced a target of 600,000 heat pumps, per year by 2028. Let’s explore heat pumps, how they work and everything you need to think about before getting one.

Article Contents 

  • Heat pumps explained 

    • What is a heat pump?

    • How does a heat pump work?

  • Considerations before buying a heat pump

    • Costs 

    • Radiators 

    • Underfloor heating 

    • Water heating 

    • Insulation 

    • House type 

  • Heat pump advantages vs disadvantages

  • How to use a heat pump efficiently 

    • Installation

    • Summer and Winter 

    • Maintenance 

    • Electricity Tariff 

  • Heat pump FAQs 

  • Further reading 

Heat pumps explained

What is a heat pump?

A heat pump is a device that's installed outside your home to take heat from outside and pump it into your home. Tens of thousands of households across the UK have already installed heat pumps. The UK Government expects millions more to be installed over the next 15 years. Uptake in Northern Ireland has been slower but as many as 150,000 homes are expected to have heat pumps by 2030.

The source of the heat extracted by a heat pump depends on the type of heat pump you choose. Here are some of the most common options.

Air Source

Air source heat pumps - also known as air-to-water heat pumps - extract heat energy from the outside air and passes it into the home through radiators and/or under-floor heating and to a water tank for hot water. Some models of heat pump can also provide space cooling in warm weather as well.

Another, less common, form of an air source heat pump - known as an air-to-air heat pump - uses indoor air units to deliver space heating rather than radiators or under-floor heating. They typically cannot be used for hot water heating.

The system itself can either be a monobloc or a split system. The vast majority of heat pumps are fitted with monobloc systems, which have all the components contained within a single outdoor unit. The heat is then transferred inside to your central heating system and hot water cylinder. Split systems have both indoor and outdoor units, which is more efficient but takes up extra space in your home and can be more expensive to install.

Air source heat pumps are the most popular type of household heat pump in the UK. Projections of future heat pump installations in Northern Ireland focus on air source heat pumps as being the main type of heat pump used.

Ground Source

Ground source heat pumps use heat stored in the ground, which is typically 12℃. The heat is absorbed into a solution of water and antifreeze circulating in underground pipes. This heat is transferred to a refrigerant, compressed to boost its temperature, then transferred to a heating system or hot water cylinder.

Also known as ground-to-water heat pumps, these systems are suitable for most properties with enough outdoor space for the pipes to be laid (usually two-and-a-half times the area of the house). Properties without a large outdoor area may be able to use a vertical borehole instead. For properties that are close to suitable rivers, streams or lakes, a water source heat pump works in a similar way except that the pipes are submerged under the water.

There are an estimated 43,700 ground source heat pump systems installed in the UK. Ground source is currently the most popular type of heat pump in Northern Ireland.


Hybrid heat pumps are systems that combine a heat pump with another heat source. This is usually a gas, oil or LPG boiler. These are commonly found in homes with a high demand for heat or where a standalone heat pump might not cut electricity costs.

The type of heat pump used and the configuration of the system will depend on your reasons for opting for a hybrid system in the first place. In the future, hybrid systems may feature boilers that run on hydrotreated vegetable oil (HVO) rather than fossil fuels.

The Northern Ireland Housing Executive (NIHE) has run a pilot project that involved retrofitting heat pumps to create hybrid systems in some of its properties. The scheme has been expanded to include more than 300 homes.

How does a heat pump work?

Heat pumps use technology similar to  that found in air conditioning or refrigeration systems.

Here's a step-by-step guide to how heat pumps work.

  1. The heat pump moves a refrigerant through a heat exchanger, which extracts heat energy from a source.

  2. The heat makes the liquid refrigerant in the heat pump evaporate into a gas.

  3. The gas moves through a compressor. The increase in pressure causes the temperature of the gas to rise.

  4. The heated gas passes over another heat exchange surface and is either blown into the home or transferred into the central heating or hot water system.

  5. With the heat transferred, the temperature of the gas drops and it condenses into a liquid again.

  6. The process starts again.

Key considerations before buying a heat pump

A heat pump is a considerable investment, so there are lots of things to think about before installing a system for your home. Let’s look at the key considerations.

 A typical air source heat pump installation can cost £14,000, while a ground source heat pump installation typically costs £28,000. You’ll also take on servicing and maintenance costs of £150 - £300 per year.

Many installers offer interest-free credit to spread the cost. You also need to consider the cost against the potential savings on your energy bills. For households in Northern Ireland, this can be anything from an annual savings of £2,300 to a loss of £500 depending on the heating system you're replacing.


You need to think about how a heat pump will work within your home’s heating system. For example, you might want to upgrade to aluminium radiators, which heat up very quickly and radiate heat into the room much faster than steel or cast iron radiators. 

Aluminium radiators are generally slightly more expensive to buy than other types of radiator but make up for that by quickly and efficiently heating your home. For the same reasons, it’s also worth considering radiators with a large surface area. It's best to get a technical assessment from a qualified installer, who will be able to advise whether you need to upgrade your current radiators.

You can use a heat pump with an underfloor heating system, too. Although not a necessity, this helps you to heat your home more efficiently while using less energy than with a central heating system.


How will a heat pump impact your hot water system? A heat pump will heat the water in your hot water cylinder up to 55°C. This will be hot enough for washing your hands and running a bath, but it’s less than the 60°C needed to kill legionella bacteria. 

You’ll need to check whether the heat pump you’re getting runs a legionella cycle (typically in the early hours of the morning) to heat the water to above 60°C or if you’ll need to top up your hot water with an immersion heater or other heating source once a week.

Oil boilers typically heat water to around 65°C, though most homes will have their radiators and hot water operating at a lower temperature to lower the risk of scalding. With that in mind, the weekly temperature top-up — which is automated by many systems — is the only significant difference in the way you use water.


The investment in a heat pump can be wasteful if you don’t first improve your home’s insulation. To maximise the impact of a heat pump and minimise its running costs, you want as much of the warmth generated as possible to stay in your home.

That might mean upgrading single glazing for double glazing in your windows, adding more loft insulation and cavity wall insulation. You can also explore ways of draught-proofing your home and sealing up any cracks that might let heat escape.

House type 

The impact a heat pump has on your heating bills and the ease of installation will depend on your home. For example, the average air or ground temperatures where you live will affect the efficiency of a heat pump. Does your property have the outdoor space to install a heat pump or an external wall on which an air-source heat pump could be mounted? The pump will usually need to be at least one metre away from a neighbouring property.

You may need to get planning permission to install a heat pump, especially if you live in a listed building or conservation area. The size of your home — the number of radiators or the area of underfloor heating that need to be heated — is another factor to consider.

Heat pump advantages vs disadvantages

We’ve already mentioned some of the pros and cons of installing a heat pump. Let’s dig into the advantages and disadvantages of installing a heat pump in more detail.


Advantages Disadvantages
Up to four times more efficient than gas boilers.

Low-carbon form of heating.

Bring down your heating costs in the long term.

Safer than a combustion heating system.
Long lifespan and low maintenance costs.

Can be used to provide cooling as well as heating

Increase property value                                                                                      
High initial costs to install a heat pump.

Complicated installation process that may involve digging up your garden.

Takes up space in your garden and/or inside your home.

Lower efficiency in very cold weather.


How to use a heat pump efficiently 

Heat pumps are a great way to make your home more energy efficient and help to reduce your electricity bills. But to do that, you’ll need to follow these tips to use your heat pump efficiently.


Make sure your heat pump installation is carried out by an experienced contractor who can install a system that maximises efficiency and performance. To give yourself the best chance of doing this, check the Microgeneration Certification Scheme (MCS) website and the Competent Persons Register to find reliable, knowledgeable installers in your area.

Adjust Controls in Summer and Winter 

Check the settings of your heat pump to make sure you're getting the most out of it all year round. Usually, this will mean setting your heat pump to a comfortable temperature in winter and letting the system maintain that steady temperature. Avoid ‘auto’ modes which will fluctuate between heating and cooling to maintain a precise temperature.

Prioritise Maintenance 

Heat pumps need to be regularly maintained to keep working efficiently and maximise their lifespan. This will typically involve an annual service and inspection of the water pump, pipes, fittings and electronics. Ground source heat pumps need to have their antifreeze and pressure checked every two or three years, too.

Choose the Right Electricity Tariff 

Your choice of electricity tariff can also optimise the efficiency of your heat pump. Power NI’s 100% Green Eco Energy ensures the electricity powering your heat pump comes from renewable sources. 

You’ll also get access to Power NI Perks. You’ll get discounts and cashback deals from B&Q and other retailers when buying aluminium radiators, underfloor heating systems and other items that help you to get more from your heat pump. 

Find out more about switching to Power NI Eco Energy to get the most out of your heat pump.

Heat Pump FAQs  

How do heat pumps work in cold weather?

The refrigerant used in most heat pumps is significantly colder than outside temperatures in Northern Ireland, even in cold weather. That means the heat exchange process used by heat pumps works in temperatures as low as -10°C for air source heat pumps and -8°C for ground source heat pumps temperatures (bearing in mind the ground temperature is usually significantly higher than the outside temperature).

Why are my air source heat pump radiators not hot?

If there’s a fault with your air pump, the system will tell you. This could be due to debris or damage stopping the outside unit from working properly. Check for any blockages outside. If the system doesn’t notify you about a problem, it’s probably unrelated to your heat pump. This could be a problem with your central heating system or your radiators needing to be bled.

Keep in mind that air source heat pump radiators never get as hot as those heated by gas or oil-fired boilers. They operate more efficiently to  maintain a steady, comfortable temperature and don’t need to be as warm to the touch.

Should I leave my air source heat pump on all the time?

Yes, it’s best to leave your air source heat pump running all the time. You might want to turn the thermostat down slightly overnight or when leaving the house but generally it’s more efficient to maintain a constant temperature. If you turn your air source heat pump off completely, it will have to work harder to get back up to temperature so it’s best to avoid drastic changes.

Do you need planning permission for an air source heat pump?

Most air source heat pump installations are a permitted development and don’t require planning permission. But it's always best to check with your local planning office first because some properties — especially listed buildings and those in conservation areas — may need planning permission.

Should I turn my heat pump off while on holiday?

Heat pumps have a holiday mode that performs the same job as turning your thermostat down slightly. It’s best to avoid turning it off entirely because big drops in temperature  will force your heat pump to work harder when it’s turned back on.

What can cause a heat pump to break?

Frequently switching a heat pump off and on again, extremely cold temperatures, faulty pumps, broken valves, debris in the system, poor quality antifreeze and incorrect pressure could all cause a heat pump to break. Regular maintenance will help you to avoid most of these problems.

What do I do if my heat pump is not working?

If your heat pump is not working it’s best to contact the manufacturer or installer for advice on what is causing the problem. Most systems have displays that show warnings if something goes wrong. It might turn out to be a problem with your heating system, not the heat pump itself, which can be easily resolved.