Installing radiators to work with heat pumps

While underfloor heating might be considered an effective way to maximise the performance of a heat pump system, modern radiators can also work very well – provided they have been sized correctly. Steve Alldritt from Energy Efficiency at City Plumbing explores the key things that installers need to consider when fitting heat pumps combined with radiators.

Homeowners across the UK are increasingly turning towards more efficient heating solutions. With several policies and incentives set to create higher demand for heat pumps, the number of retrofit projects is likely going to increase. This will no doubt be compounded by gas prices as they continue to rise.

Unlike gas boilers, heat pumps work at lower flow temperatures, typically ranging from 40°C flow up to 50°C flow depending on the application. This temperature makes it the optimal partner of underfloor heating which works best at flow temperatures of between 35°C and 50°C, but not every home is suitable for underfloor heating, and not every homeowner will have the budget to incorporate it into the project. Laying screed floors can be timely and disruptive, and while there are overlay options that are quicker to install, sticking with radiators can still be preferred.

Key considerations

Specifying radiators for use with heat pumps is practically the same as specifying them with gas boilers but it’s crucial that installers carefully consider heat loss to avoid costly mistakes further down the line. First, consider the position of existing radiators and whether there is space to replace these

Cut To The Chase

 The calculation of heat losses is critical before the installation of radiators

 Radiators will not be suitable if microbore pipework drops are present in the existing system

 To achieve the same output on a heat pump system, it is likely that existing radiators will need to be replaced with a bigger size

 Triple-panel radiators deliver a high heat dispersion but take up less wall space

 High-temperature heat pumps could be an option to consider with larger units if necessary. Also, examine the size of the wall cavities, the level of insulation within them, and ensure the loft insulation is 200mm thick or more as standard.

Pipework will also be a key consideration – if microbore pipework drops are present in the existing system, radiators will not be suitable.

The quality of the building’s glazing and window profi les will also make a huge difference to whether radiators can be used with the system. Single glazing is a defi nite no-no, and in some cases upgrades to the existing double glazing may also be required.

Sizing up

Once the building has been deemed suitable for radiators, it’s time to look at replacing the existing ones with options that will be suited to the lower flow temperatures associated with heat pumps.

In some cases, the property’s thermal performance may mean that the existing radiators are suitable for the job. In these instances, it is advisable to power flush the system to remove any sludge or debris that might impact the performance of the new system.

Where radiators do need replacing, it’s important to apply the manufacturer’s Delta T correction factors when sizing. For example:

• For a 75°C flow temperature, a typical 600mm H x 700mm L Single Panel Single Convector radiator will give approximately 0.656kW of output.

• If we put 45°C flow through the same radiator, a correction factor of 0.365 needs to be used.

• 0.656 x 0.365 = 0.251kW.

• To achieve the same output, the radiator would need to be replaced with a bigger size. (In this instance a 600mm H x 1100mm L Double Panel Double Convector radiator would need to be installed, providing approximately 0.656kW).

Available options

Where the existing radiators aren’t suitable, installers may choose to install fan assisted radiators, although the radiator will need an electrical connection. Fan assisted radiators are a modest way to blow warm air around the room and distribute heat more evenly while keeping energy consumption low.

For radiators with no electrical connection nearby, another option is to choose deeper, triple-panel radiators which have a high heat dispersion but take up less wall space. Vertical feature radiators can also be a stylish way for homeowners to balance aesthetics with a higher output.

Other considerations

Heat pump installations, even with the help of government subsidies, are a heavy investment for many, and sometimes customers may insist on keeping their existing radiators despite recommendations for a resize. At this point, it may be worth exploring high-temperature

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 Vertical radiators can be a stylish way to balance aesthetics with a higher output heat pumps that can run up to 75°C. These heat pumps run at similar temperatures to boilers and, as such, there would be less of a need to upsize radiators.

As with all heat pump installations, the pump unit needs to be located as close to the building as possible and with a metre clearance on all sides. It’s also crucial to avoid mounting the unit on north-facing walls. These considerations help to put less strain on the system and help it to operate more efficiently.

While it won’t affect the performance, it’s also important the installation doesn’t take place close to bedroom windows, as the unit can produce a little noise, which may disturb at night.

Space for a heat pump-ready cylinder, buffer tank (usually between 20L and 50L), a volumiser and the relevant control equipment are other elements that also need to be considered.

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City Plumbing Supplies offers a wide range of essential products from boilers and circuit breakers to heat pumps and bathroom suites. This includes a dedicated team of specialists with over a decade of expertise in renewable technology who can help installers design and specify renewable systems and can recommend the best products for every application.

Energy Efficiency at City Plumbing has also opened a new Energy Efficiency Centre after agreeing on a partnership with GTEC Training to provide accredited training courses for installers. The Centre, based in Farnborough, will focus on showcasing renewable energy home heating technologies and providing training for engineers to install them.

STELRAD. YOUR FIRST CHOICE FOR A RENEWABLE FUTURE.