Yes, air source heat pumps (ASHPs) can be retrofitted into existing or older properties - not just new builds. However, for the heat pump system to perform efficiently and meet the heating demand of these homes, installers must ensure sufficient energy efficiency measures are in place and that the system has been accurately designed. This blog explores the topic of retrofitting heat pumps and the important installation steps installers need to follow.
As demand for sustainable heating solutions grows, more homeowners are turning to low carbon options such as heat pumps. Retrofit heat pump installations are increasing so more heating engineers are expanding their skills to meet this growing demand.
In this guide, we will explore:
- What is retrofitting
- What makes a home suitable for a heat pump
- The importance of thorough planning and design
- Retrofitting a heat pump to existing boilers and heat emitters
- How installers can upskill and develop their heat pump knowledge
With the right approach, retrofit heat pump installations can deliver excellent comfort to your customers and their homes while also helping them to reduce their carbon footprint.
What is retrofitting?
In the heating industry, the term retrofitting refers to installing a new, often more efficient, heating system into an existing property. While new builds account for a significant proportion of annual heat pump installations, the retrofit market is considerable and just as important. If the UK is to hit its net zero carbon targets, it is essential to reduce the carbon footprint of heating systems in existing housing stock.
Retrofitting heat pumps is not just about the environmental benefits - the retrofit market also offers significant opportunities to installers. By offering sustainable, low carbon alternatives like air source heat pumps, heating engineers can expand their services and meet the growing demand from homeowners who want to replace their traditional boilers with greener technologies.
From period homes, mid-century properties or more recently built homes, retrofitting a heat pump allows homeowners to upgrade their heating, lower their dependency on fossil fuels, and reduce their impact on the environment.
Retrofitting a heat pump - what you need to know
Retrofitting a heat pump is not the same as simply fitting a replacement boiler. Unlike gas or oil boiler systems that operate at higher temperatures, air source heat pumps are low temperature heating systems and this fundamental differences affects how they are installed and how they perform.
Why planning matters
To ensure a heat pump works efficiently in an existing property, a bespoke system design is essential. Installers should work closely with the homeowner to understand:
- Their customer's comfort levels and temperature preferences
- Their customer's hot water demand
- The heat loss of the property.
With careful planning, correct system design and setup, a retrofit heat pump system can provide your customers with a highly energy efficient heating system with sustainable and environmentally friendly benefits as well.
Considerations of older homes
Depending on the property's age, construction type, size and existing insulation levels, some upgrades to the system or wider property may be recommended. For example:
- Energy efficiency improvements, such as double glazing, loft insulation or cavity wall insulation help reduce the amount of heat escaping from the home, helping the heat pump's efficiency and effectiveness.
- Radiators may need to be replaced with larger models or units designed for low temperatures systems, such as aluminium radiators.
- Underfloor heating may be installed, again offering a larger surface area for distributing heat into rooms.
- The system pipework may also need to be upgraded with larger pipe and improved insulation to better support the heat pump's flow requirements.
Tailored to each home
It is important to note that not every retrofit heat pump installation will require all these upgrades. Every home is different which is why a detailed property survey and installation plan should be produced based on a property’s individual requirements and specification. This is essential to get the best performance out of a heat pump system.
Key steps for installing an air-to-water heat pump
Whether you are retrofitting a heat pump into an existing home, incorporating it into a renovation or extension, or installing a heat pump in a new build, following a clear set of steps is crucial for a successful installation. Here are four key steps that every heat pump installer should follow.
Conduct a detailed heat loss calculation
Understanding the property's specific heat loss and fabric efficiency is the basis for planning an efficient system design.
Design the system accurately
Choose the correct heat pump output and size, and specify the appropriate heat emitters for low temperature operation. Grant UK's in-house Design Team can support installers with heat loss calculations and system specifications.
Install the system correctly
Follow the manufacturer's installation instructions and ensure that all regulations are complied with. The standard of an installation can impact the heat pump's performance and efficiency if not completed correctly.
Complete a thorough handover with the customer
Educate the homeowner on how to use the system, explaining what living with a heat pump is like and making sure they are confident with the heat pump controls and settings.
For more in-depth information, visit our dedicated blog on best practices for heat pump installation.
Can you add a heat pump to an existing boiler?
Yes, with a hybrid technology, you can.
An air source heat pump can be integrated with an existing fossil fuel boiler by using a hybrid system such as the Grant EvoLink Hybrid System Hub. This is an ideal solution for properties where installing a standalone heat pump may not be feasible due to high heat loss or limited potential for upgrading heat emitters.
Benefits of a hybrid heating system
- Reduces a household's reliance on fossil fuels
- Helps lower carbon emissions
- Uses renewable energy to fulfil a proportion of the heating and hot water demand with the traditional boiler serving as a back-up heater
The Grant EvoLink is a compact, wall mounted, white cased unit which houses the necessary hydraulic components to connect an Aerona³ R32 air source heat pump with most types of existing boilers - including gas, LPG and oil.
The EvoLink intelligently controls both the heat pump and boiler, prioritising the heat pump to meet as much of the home's heating and hot water needs as possible. The boiler only steps in as a supplementary heat source, ensuring optimal comfort.
If you have customers with traditional boilers who want to reduce their carbon footprin, the EvoLink Hybrid System Hub offers an innovative and flexible solution.
Learn more about the Grant EvoLink, including free online training for installers.
Can new heat pumps work with existing radiators?
Yes, new heat pumps can work with existing radiators but there are a few important considerations to ensure the system runs efficiently and delivers the desired comfort levels.
When can existing radiators be used?
Many homes already have radiators installed and, in some cases, they can remain in place when upgrading to a heat pump. Since air source heat pumps are low temperature systems, they operate differently compared to traditional high temperature boilers (such as oil or gas) so heat pump systems may require:
- Larger surface areas to deliver the same heat output (in these cases, you may need to fit additional radiators for example)
- Radiators which are compatible with heat pumps (some radiator types are not suitable for heat pumps so in these instances, new heat emitters will be required)
Read our guide on advising homeowners about the best radiators for air source heat pumps.
Where can heat pumps be installed?
It is a common misconception that heat pumps are only suitable for new builds. In reality, heat pumps can be installed in a wide range of properties, including existing homes or larger buildings like farmhouses. They are also an excellent option for properties currently heated by a gas central heating system or homes undergoing renovation.
You can read real-life examples of retrofit heat pump installations in our case studies:
- Aerona³ 10kW heat pump upgrades Wiltshire farmhouse heating system
- Grant renewable heating system helps family reduce their energy costs
- Aerona³ heat pumps take heating to a new level
As mentioned earlier in this blog, retrofit installations may sometimes require additional measures to ensure the property is ready for a heat pump. Factors such as insulation levels (walls, roof and windows), available outdoor space for the unit, and the overall heating and hot water demand of the property all play an important role.
Find out more about what types of homes are suitable for air source heat pumps.
Why should your customers switch to a heat pump?
Making the move to an air source heat pump offers a range of benefits for your customers, from lowering their carbon footprints through to improving the efficiency of their home heating. Heat pumps are highly efficient, environmentally friendly and can provide reliable heating and hot water all year round. Furthermore, with Government grants and funding available, financial support is available to help consumers switch to greener heating systems.
Read more about the advantages and considerations for heat pumps in our dedicated heat pump guide.
Looking to expand your skills?
With demand for air source heat pumps growing, now is the perfect time to upskill. Whether you are an experienced heating engineer or starting your career, heat pump training can open new opportunities, helping you to meet customer demand and stay ahead in the evolving heating market.
How to become a heat pump installer
In June 2024, NESTA published the results of their heat pump installer survey, revealing that 87% of respondents wanted to increase the number of heat pumps they install each year (NESTA, 2024). The survey also showed that employers are looking for installers with a higher level of practical heat pump installation experience.
For experienced heating engineers and those new to the industry, a good place to start is to complete heat pump product training. These training courses provide an introduction to how heat pumps operate and offer valuable hands-on experience with the units themselves. At Grant UK’s Training Academy, for example, courses combine theory with practical workshops to help installers gain the confidence and skills they need out in the field.
Installers looking to achieve MCS accreditation for heat pumps - which is a requirement to install heat pumps under the Boiler Upgrade Scheme - will also need to complete industry qualification courses. One such course is the OFTEC OFT21-504A qualification which covers installation, commissioning and servicing of air source heat pumps. Successful completion of this course enables installers to apply for OFTEC heat pump registration and for MCS certification for work carried out under the scope of MIS 3005-I.
Air source heat pump training courses with Grant UK's Training Academy
At Grant UK, we deliver air source heat pump training throughout England, Scotland and Wales. Our courses are designed to help heating professionals confidently install, commission and maintain heat pumps, while also offering training on hybrid systems, solar thermal, underfloor heating and hot water storage solutions.
Our Training Academy HQ in Swindon, Wiltshire, is also an approved OFTEC training centre, equipped with state-of-the-art facilities including hands-on workshops, interactive learning screens, air-conditioned theory rooms, and dedicated assessment areas for practical evaluations.
Ready to take the next step? Start your journey into heat pumps today - learn more about our award-winning Training Academy and discover the full range of Grant air-to-water heat pumps and accessories.
This blog was originally published on 8th August 2024 and updated on 15th May 2025.