Air source heat pump heating systems work differently to traditional fossil fuel boilers and selecting the right choice of heat emitter, such as radiators, is key to helping a heat pump system to achieve its optimum efficiency. In this article, we share a heating engineer’s guide to inform homeowners about what they need to know when it comes to choosing radiators for air source heat pumps.
A misconception held by some is that radiators do not work with air source heat pumps. While it may be true that some radiators are not suitable, the important factors when it comes to radiators and their compatibility with heat pumps are their size and their material. In this guide, we want to talk you through some of the key considerations when it comes to choosing suitable radiators for an air source heat pump including
• Radiator design and compatibility
• Sizing radiators for low temperature systems
• Radiator material options and their efficiency
What is an air source heat pump (ASHP)
As we are focusing on the topic of radiators for heat pumps, a good place for us to start is by explaining what an air source heat pump is and why you may consider one for your home. Summarised very briefly, an air source heat pump extracts the heat energy which is in the air outside and converts it into energy that can be used within your home to heat your rooms and provide hot water.
Heat pumps are very efficient units, producing more energy than they use – for example, for every kilowatt of energy that the Grant Aerona³ R32 6kW heat pump uses to operate, it produces over 4kW of energy that it puts into a heating system (based on average climate conditions). Furthermore, heat pumps do not use fossil fuels and instead use electricity to run which means that they are a more sustainable heating solution and can help reduce carbon emissions. These benefits are just two of the reasons why heat pumps are becoming increasingly popular here in the UK and why the Government is encouraging the uptake of low carbon, electric heating.
Visit our Education Area to read more about how an air source heat pump works.
Understanding air source heat pumps and radiator compatibility
You will often hear a heat pump referred to as a low temperature system and, as a result, it is crucial that a suitable selection of heat emitter is specified and installed. Let’s delve into this in more detail.
How do ASHPs differ from conventional boiler systems
Air source heat pumps typically operate at lower flow temperatures which means the water flowing around the system (through the radiators or an underfloor heating system) will be cooler than the water flowing in a system connected to a gas boiler. Heat pump systems operate more efficiently at lower flow temperatures, typically at 35ºC and up to 55ºC, whereas a traditional boiler system will have a flow temperature of between 70ºC-80ºC. Due to the reduced water temperatures, a larger surface area is needed to transfer the heat from the system into rooms within your home and this is why radiators installed with a heat pump need to either be larger or be specifically suited for low temperature operation.
It is important to stress that a low temperature heating system will keep your home just as cosy as a high temperature system, provided your heat emitters have been sized and specified correctly. Watch our video here to learn more about living with a heat pump.
Key considerations for radiators
When choosing new radiators for your home, whether you have a traditional boiler or an air source heat pump, there will be some important considerations you need to factor in. Firstly, what is the efficiency of the radiator and how effective it is at warming up and subsequently emitting heat into your rooms. Secondly, does the radiator’s design deliver with the aesthetics to suit your home but also in functionality, with maximum surface area for heat transfer. Thirdly, is a radiator compatible with your heating system and, in particular, with a low temperature heat pump.
Types of radiators suitable for ASHP systems in the UK
There are lots of types of radiators and many of them will be suitable for air source heat pumps – below, we have focused on just four types of air source heat pump radiators.
Panel radiators
A panel radiator can be found in thousands of homes and they are widely used in modern installations. Panel radiators have a slim design and are usually a cost-effective option to purchase. While they can operate with lower flow temperatures (if they are sized correctly to achieve the required output), they may not be as efficient or effective as other radiator types connected to a heat pump system.
Convector radiators
A convector radiator (pictured below) differs to a panel radiator because it features an additional layer of metal fins, usually positioned inside the radiator. These fins are heated up evenly and increase the surface area of the radiator, producing more heat and are therefore better designed to complement a low temperature heat pump compared to a traditional panel radiator option.
Designer radiators
As their name suggests, designer radiators are more stylish with their aesthetics appealing to homeowners looking for more than a white radiator for their walls. Designer radiators are available in a wide choice of colours and styles, becoming statement pieces within a room. Alongside their style, designer radiators are also functional but as they vary in design and material, it is always worth checking with the manufacturer to ensure they are suitable as air source heat pump radiators.
Grant’s Afinia range of energy efficient radiators combine sleek and stylish designs with effective functionality to complement low temperature heat pumps. Discover our Afinia radiator range here.
Low temperature radiators
Low temperature radiators are those which are specifically designed to operate on heating systems with flow temperatures of 35ºC-55ºC. Specially engineered to work efficiently with lower flow temperatures, these radiators are well suited to air source heat pumps.
Key factors in selecting the right radiator for your room
When you are considering new radiators, we would recommend speaking to your heating engineer to discuss the different options available because there are several factors which will determine which radiator type and size is best suited to your home.
Assessing room heat loss and demand
In order to know what radiators you need, you first need to ascertain how much heat is escaping from your rooms and what is the temperature demand for each of your rooms that the heating system will need to fulfil. To ascertain this heat loss and demand, your installer will carry out a thorough heat loss calculation.
Calculating heat loss
To calculate the amount of heat being lost from a home, a heat loss calculation must be completed for each of your rooms. This will factor in the size of the room, including ceiling height, the quality of insulation in the walls as well as in the floors and roof (when applicable) and the calculation will also consider the number of windows and whether they are single, double or triple glazed.
Determining required output
Once your installer has worked out how much heat is being lost from each of your rooms, they will be able to determine the heat input required to satisfy each room and decide what radiator output and size is needed. At this stage, it is important that your installer understands your temperature preferences as well because if you prefer warmer room temperatures, they can ensure that your radiators are sized appropriately to fulfil this demand.
Radiator sizing and placement
To ensure your radiators can effectively keep your home as warm as you like it, they need to be correctly sized and appropriately positioned in each of your rooms.
Sizing considerations
Radiators installed on low temperature heating systems will typically need to be larger than those on a high temperature system. When calculating the appropriate surface area of your radiators, your installer will need to select the correct delta T from the performance data (for Grant Afinia radiators, this performance data is supplied in the installation manual). It is worth knowing that our in-house Design Team can help your installer not just with the sizing of your radiators but also the wider specification of your complete heating system.
Placement and aesthetics
When choosing where to position your radiators, your installer will consider the amount of wall space available, the furniture within a room and they will also need to adhere to the clearance guidelines provided by the radiator manufacturer. For example, with Grant Afinia radiators, these must be positioned more than 100mm above the floor and at least 120mm distance away from overhangs such as windowsills or shelves. It is also important to let your installer know if there are particular parts of a room where you do not want a radiator, so that they can factor in your room’s layout and décor where possible.
Efficiency, material and performance ratings
How effective a radiator is at emitting heat into your rooms will be determined by their design (as touched on above when we looked at panel, convector and designer radiators) as well the type of material they are made out of.
Material options
Radiators are typically made from steel, iron or aluminium. Panel radiators are commonly made from steel whereas iron or cast iron is a popular choice for designer radiators. Of the three material choices, aluminium has excellent thermal conductivity properties and this is why aluminum radiators, such as our Afinia range, are more efficient than traditional cast iron or steel radiators. In addition to being great conductors of heat, aluminum radiators have a low water content which means they are highly responsive to any changes in the temperature demand, warming up and cooling down rapidly.
Performance ratings
When your installer is calculating radiator sizing for low temperature heating, they will refer to the performance data of the specific radiator model they have in mind. For the Grant Afinia aluminium radiators, the performance data for each radiator model is available in the installation manual.
Top radiator recommendations for ASHP Systems
As part of the package solutions offering that Grant UK supply, we recommend a choice of either aluminium radiators or underfloor heating systems to suit air source heat pump systems. If you are interested in reading more about the pros and cons of these two choices of heat emitters, please read our blog here – Underfloor Heating or Radiators – which option is best for you.
As we are focusing on radiators which are suitable for heat pumps, we will now take a closer look at aluminium radiators and why they partner so well with air source heat pumps.
Aluminium radiators and why they complement heat pumps
Grant Afinia radiators are available in horizontal and vertical options and are supplied in different section length combinations. This means they can suit larger rooms where a bigger radiator is required as well as smaller areas or restricted wall spaces where either a small radiator or slim radiator is better suited.
If you are interested in reading more about Grant aluminium radiators, we have shared some useful links below:
• Read a case study about a loft conversion where Grant Afinia vertical radiators were installed
Installation and maintenance considerations
Installing Grant’s aluminium radiators is quick and easy. The Afinia radiators are light in weight and their installation and fitting can be completed by a single engineer.
Professional installation
The installation of Grant Afinia radiators should be carried out by a suitably qualified professional or other competent installer in accordance with the relevant British and European Standards and all applicable Building Regulations. The radiators must not only be fitted in accordance with the installation instructions but the installer must also correctly connect the radiators to the wider system and commission the system in accordance with the guidelines provided in BS 7593.
If you are looking for an installer to quote a new heating system or to fit new radiators in your home, please use our Find an Installer online search to research local G1 Installers in your area.
Maintenance tips
Aluminium radiators are low maintenance. They may sometimes need bleeding, like most types of radiators, and you can read more about how to bleed an Afinia radiator in our Customer Support Centre for aluminium radiators. In addition, when your heating engineer services your heat pump, they can also carry out some steps to check that your radiators are working well. Our infographic below summarises the servicing checks involved in caring for underfloor heating systems and radiators.
Frequently asked questions
We have shared a few commonly asked questions here relating to radiator installations for air source heat pumps but to view more FAQs about aluminum radiators, please head to the FAQ section of our Knowledge Hub.
Q: Can I use a standard radiator with an ASHP in the UK?
A: Standard radiators, such as steel panel radiators, can be fitted with an air source heat pump but they may need to be oversized in order to transfer the required amount of heat into the room from the lower operating temperature of an ASHP.
Q: How do I know if a radiator is suitable for low temperature systems?
A: The radiator’s manufacturer will confirm whether a radiator is suitable for low temperature systems – typically, this information will be provided in the sales brochure and technical literature for the radiator.
Q: What benefits do low temperature radiators offer?
A: They are optimised for energy efficiency especially at lower flow temperatures of between 35ºC-55ºC, delivering the desired heat output to achieve the temperature settings for each room.
Choosing the right radiator with Grant UK
We hope you have found this detailed guide of interest as part of your research for air source heat pump radiators. The correct choice of heat emitter and their appropriate sizing is as important as correctly specifying the heating output of the heat source itself. It is important to thoroughly plan a new heat pump heating system to ensure that it can operate efficiently and fulfil your heating requirements as effectively as possible.
If you are ready to take the next steps to find an installer who can quote you for a heat pump system, including radiators, then please use our online Find an Installer search tool. You can also read more about the Grant Afinia aluminium radiator range here.