How to buy an air-to-water heat pump

Most UK homeowners have never owned or used a domestic air-source heat pump before; in fact, you've probably never even seen one in action.

If you're considering installing an air-to-water (or hydronic) heat pump as a replacement for your current heating system, here's everything you need to know about the buying journey.

The ultimate goal is to end up with a heating system that's right for your home: one that supplies heating and hot water when you need it, efficiently and affordably. 

You'll need to know what's available, and the key features to look out for, to make sure it suits your household's needs.

We've also compiled a table comparing the main brands currently operating in the UK market, to give you a better idea of their key similarities and differences.

Not quite ready to choose your air-to-water heat pump? See our guides to: how heat pumps work and the potential costs and savings.

Choosing the right heat pump installer

The most important factor when choosing a heat pump for your home is working with a good installer. 

A heating system is not a simple off-the-shelf product; it should be custom-engineered for your home. 

While the heat pump itself - like a gas boiler - might be a standard unit, the system design, installation and set-up will be unique to your home. It should take account of the building's construction and insulation, room sizes, local climate, and your existing heating system.

Your heating engineer must carry out a full heat loss calculation for your home. This helps to ensure that your heat pump is correctly sized to supply the right level of heating, and sufficient hot water to meet your needs, whilst operating at maximum efficiency. 

The engineer should then design the entire heating system, including the heat pump and any additional components such as a hot water cylinder; the emitters (radiators and/or underfloor heating) to deliver sufficient heat to each individual room or area; controls; and the pipework that connects everything together.

Once the system is installed, your engineer will commission it. This means switching on the heat pump and testing the system to ensure it is working correctly. 

Your heat pump installation is not complete until it has been tested and adjusted to run safely and efficiently. You should receive a commissioning report, along with user manuals/guides and warranty documents. 

We asked heat pump owners for their thoughts about their installations and their advice for others taking the plunge: find out what it's really like to have a heat pump.

Heat pump installer qualifications and certifications

If you are applying for a government grant for your heat pump (through the Boiler Upgrade Scheme, or Home Energy Scotland, for example), you'll need to use an MCS (Microgeneration Certification Scheme) registered installer. This is mandatory to receive the grant.

MCS accreditation is not legally required for all heat pump installations. If you don't plan to claim a grant, it's not absolutely necessary. However, you should make sure the installer has the correct qualifications.

Installation of any air-source heat pump must comply with Building Regulations. Your installer will need to be suitably qualified to undertake the necessary plumbing and electrical work.

An MCS certificate acts as proof of quality assurance for building control notification, as well as for home insurance cover. Alternatively, the installer may self-certify their work if they belong to the relevant Competent Person Scheme. 

You should also check that your installer is a member of one of the recognised consumer codes, which offer deposit protection, insurance-backed guarantees and dispute resolution if something goes wrong. Both RECC (Renewable Energy Consumer Code) and HIES (Home Insulation & Energy Systems Quality Assured Contractors Scheme) are approved by the Chartered Trading Standards Institute (CTSI).

Many installers also describe themselves as 'manufacturer accredited'. This means that, in addition to the required qualifications, they have undertaken training with one or more manufacturers to install their brand of heat pumps. A manufacturer-accredited installer should have a good level of knowledge about the heat pump itself, and you are likely to receive a longer product warranty. 

Find out more about the Boiler Upgrade Scheme and how to apply.

How to find a heat pump installer

You can find an MCS-certified installer near you by searching the database on the MCS website. 

Which? Trusted Traders are all MCS accredited, and have also passed our assessment process including credit, reference and background checks. 

How to choose a heat pump brand 

We asked Trusted Trader engineers who had installed, serviced and/or repaired hydronic heat pumps in the previous three years for their top tips for potential heat pump owners.

One engineer told us:

'All heat pumps work regardless of manufacturer. However, the heat loss survey and design must be done correctly. The installation must be carried out by experienced qualified engineers and the system supported by the company that installs it.'

Expert installation and understanding how to operate your system are just as important as the make and model that you choose.

There are, however, some key features to be aware of when selecting your heat pump.

The most important heat pump features to consider

In an online survey in June 2026, we asked 1,096 Which? Connect panel members what features would matter to them most when shopping for a heat pump. 

More than half (51%) identified a long warranty as being an important feature. This is not surprising given that heat pumps are an unfamiliar technology, and are designed to last a long time. A long warranty offers peace of mind in case something goes wrong. 

Around 40% of respondents rated a performance guarantee, quiet operation, and good energy efficiency as being important.

Here are the criteria you'll need to consider when selecting your hydronic heat pump:

Heat pump manufacturer warranty

All heat pump manufacturers offer a free parts and labour warranty, but the warranty length can vary from just two years up to eight years. 

The maximum free warranty is usually available when the heat pump is installed by an in-house or manufacturer-approved engineer. 

Check the length of the free warranty when getting quotes, as you may be offered a longer period by the installer. There is usually an option to pay for an extended warranty too.

Performance guarantee

Some manufacturers offer a performance guarantee with their heat pumps; your installer may also offer one. 

This guarantee will normally state a minimum level of efficiency that your heat pump must reach, whilst also providing the promised level of heating and hot water.

Even if you don't have a performance guarantee, your heat pump should deliver the designed temperature to each room. If it's not working in the way you expected, contact your installer as they may need to make some adjustments.

Noise

A typical domestic heat pump produces a sound power level around 50-60dB (decibels). For comparison, an average refrigerator produces a background hum at around 35-45dB.

Owners tend to report that they make the most noise when they are working hardest - during the cold winter months. 

It’s worth considering a quieter model if your heat pump will be located near to your property boundary, to reduce the likelihood of disturbing your neighbours.

Energy efficiency

Energy efficiency is one of the most important factors when choosing any heating system, as it affects how much energy you use to heat your home and hot water, which in turn determines your energy bills. 

Because heat pumps use electricity, which is more than three times the price of gas, an inefficient heat pump can prove very costly.

The efficiency of a heat pump is generally expressed through its Seasonal Coefficient of Performance (SCOP), which is a measure of its average efficiency across varying conditions over an entire year. The higher the SCOP, the more efficient the heat pump.

You will see different SCOP figures quoted depending on the flow temperature. Systems with standard radiators often operate at around 55C, while those with underfloor heating can operate more efficiently at a lower temperature of around 35C.

Refrigerant type

Many modern heat pumps now use a less environmentally harmful refrigerant called R290, a highly efficient form of refrigerant-grade propane with a very low global warming potential (GWP 3).  

Others still use R32 (an F-gas, difluoromethane), which has a much higher GWP of 675 and is being phased out in domestic heat pumps. However, R32 gas will remain available for servicing existing units for the foreseeable future.

Range of sizes

A wider range of sizes means you are more likely to find a model that's exactly right for your home; however, it's more important to know what size you need in the first place. 

Installer network

Many heat pump manufacturers have a UK-wide network of trained, accredited installers. This can be helpful as you may benefit from a longer free warranty if you use a manufacturer-accredited installer. It's also useful to have a local engineer on hand for servicing and repairs.

Other considerations

Other factors you might consider when choosing your heat pump include:

• Apps and controls - heat pumps are supplied with software to monitor and control your heating and hot water. These are often proprietary apps that allow you to manage your heating schedule, adjust the flow temperature, and track the performance of your heat pump. Some can be integrated with popular smart home hubs and dynamic energy tariffs; if you already use these, and integration is important to you, check that your heat pump app will be compatible.
• Dimensions - do you have a limited space in which to fit your heat pump? Some models are smaller than others, while some have different proportions (wider and shorter, or narrower and taller, for example) that may fit your requirements better.
• Appearance - if the look of the heat pump is important to you, shop around to find one you like. Many are only available in one colour/finish, but some brands offer a wider range of options. 

Heat pump brands compared

Hydronic, air-to-water heat pumps are the most common type of heat pump fitted in UK homes. 

They are popular because they can often directly replace a gas or oil boiler, supplying both heating and hot water, and can often (though not always) reuse the existing pipework and radiators.

We've looked at some of the most popular hydronic heat pump brands to compare the features available.

In July 2026, we asked 19 companies for information about their most popular range of domestic hydronic heat pumps in the UK. For comparison, we requested data on the model size closest to 8kW, which is the average size installed in British homes, according to the government’s Boiler Upgrade Scheme data. 

Ten companies supplied information. We've listed them in the table below alphabetically, with details alongside the specific range and model. 

The manufacturers listed may also supply other hydronic heat pump ranges with different specifications.

Where to buy a heat pump

You can choose whether to purchase a heat pump through a local independent installer or through a large company. 

Some of the big UK energy firms offer heat pump installation packages, and sometimes offer exclusive insurance packages or access to competitive heat pump tariffs to customers who use this route. 

As with any expensive home improvement project, we'd always recommend that you get a handful of quotes from companies of different sizes so that you can compare what's on offer and get a feel for what is most important for your home. 

For more information on where to buy heat pumps, as well as details of costs, potential savings and financing options, head to our guide to air source heat pump costs and savings.

Get personalised energy advice for your home

If you're still weighing up your options, or want to see what the costs and savings could look like for your home, you can use our free, personalised home energy planning tool. 

Using your home's EPC data and other information you give, we can show you what types of energy saving technology could work for you, and what your household bills would look like on an ongoing basis. 

You'll get tailored help with your home, and you can save your energy plan to return to at any time.

Find out more and start your home energy plan now.