Air Source Heat Pumps & Radiators (FAQ)

In Summary: Our Air Source Heat Pump & Radiator FAQ

Not got time to read our full FAQ covering air source heat pumps and radiators? Read this summary instead…

Heat pumps will work with radiators, and they can be incorporated into a hybrid system that uses underfloor heating.

However, it’s worth noting that flow temperature on heat pumps is usually set at 35°C-55°C, whereas a gas boiler is usually set to 70°C. 

So, whilst you can use existing radiators, renewing them for larger and more efficient ones is advisable. Typically, radiators used with heat pumps need to be around 2.5 times bigger in terms of BTU, which usually means they’re about 30% larger in size.

This is likely to mean all or some of your radiators will need replacing for newer efficient ones. New radiators can be up to 50% more efficient, partly due to technology, partly due to build-ups in limescale and heating sludge over the years. 

Expect individual radiator installation to cost £200-£300 including materials and labour, although there are plenty of variables that affect the price. 

You can get fixed prices on-screen for your air source heat pump here; we’ll suggest radiator upgrades if you need them.

Do Heat Pumps Work With Radiators?

Yes, air source heat pumps (ASHPs) are designed to work with radiators. They can also be used as part of a hybrid system using existing radiators as well as underfloor heating.

Heat pumps work at lower flow temperatures than a typical gas boiler. As an example, a typical flow temperature for a gas boiler would be approximately 70°C. By comparison, the flow temperature set on most heat pumps is in the region of 35°C to 55°C.

By working with a bigger surface area and a much lower flow temperature, heat pumps are far more efficient than gas boilers. The most efficient gas boilers are around 94% efficient, whereas the most efficient air source heat pumps are over 400% efficient.

Will Radiators & An ASHP Get My House Warm?

Air source heat pumps working with radiators should only be installed in efficient homes. If your house is reasonably new, or has had upgrades such as cavity wall insulation or loft insulation, a heat pump coupled with radiators would work perfectly. 

On the other hand, if you live in an old stone cottage with little or no insulation, a heat pump usually wouldn’t be suitable. You’d need to upgrade your insulation. If you don’t, your heat pump will need to work overtime to keep your property warm and that’s going to mean extra electricity consumption.

Can I Use Existing Radiators With My Air Source Heat Pump?

Yes, you can use existing radiators with a heat pump but it’s not advisable. Even if your radiators are reasonably new, it’s unlikely they are the correct size.

Radiators to be used with an air source heat pump typically need to be much larger than what you’d use with a gas boiler. Output (BTU) of radiators used with heat pumps, needs to be approximately 2.5 times more than those used with a gas boiler.

This is directly linked to the flow temperature we’ve mentioned above. Whilst a gas boiler provides a flow temperature of approximately 70°C, an air source heat pump will work at 35°C to 55°C. Put simply, you need a bigger surface radiating heat to achieve the same household temperature as you would with a gas boiler.

You’ll need an MCS certified installer to spec your property and determine exactly what size radiators you need. Use our clickable heat pump tool here, and it will determine what (if any) additional or upgraded radiators you’ll need for your heat pump to work efficiently. 

How Much Do ASHP Radiators Cost To Install?

One radiator is likely to cost £200-£300 to install. However, if you’re simply upgrading a radiator using existing pipework, this cost could be reduced to around £150.

Prices will vary depending on the type of radiator you install. Bigger radiators are always more expensive, as are designer ones. 

And upgrading to a bigger radiator by replacing an existing one, is going to be much cheaper than a fresh install. This is simply due to the fact that with an upgrade, the existing pipework can be used, which saves some time for the installer and therefore, labour costs.

How Much Bigger Do Radiators For Heat Pumps Need To Be?

As a general rule of thumb, radiators for heat pumps need to be 2.5 times bigger (in terms of BTU output) than the ones in use for a gas boiler. 

So how much bigger will your radiators actually be? Obviously this depends on the specific brand and model. But typically, expect your radiators at a 2.5x output of your current ones, to be approximately 30% larger in size.

And this means that with many air source pump installations, it makes sense to install new radiators too.

Take the guesswork out of your heat pump and radiator installation. Use our clickable tool here; it will suggest the perfect heating solution for your home based on the property specs you provide.

What Are The Best Radiators For Heat Pumps?

The best radiators for heat pumps are big ones! The bigger your radiators are, the higher the efficiency level of your air source heat pump will be. 

Gas boilers work with a more “full on” approach, whereas heat pumps work low and slow. Whilst there’s a big flow temperature difference between gas boilers (approximately 70°C) and heat pumps (35°C to 55°C), pumps match gas boilers for heat output by utilising bigger radiators. 

They also work incredibly well with an underfloor heating setup; another form of heating that works efficiently at extremely low flow temperatures.

Put simply, the higher the output of your radiators, the lower the flow temperature your air source heat pump can run at to meet your heat demand. Overall, this is going to result in a huge drop in energy bills.

What Temperature Will My ASHP Radiators Run At? 

ASHP radiators work at a lot lower temperatures than when using a gas boiler. When powering radiators using a gas boiler, radiators will be hot to the touch. 

ASHP radiators won’t be hot, they’ll feel luke-warm at best. If you have a system fitted and your radiators aren’t hot to the touch, this isn’t a problem or fault, this is simply how heat pumps work to maximise their efficiency. 

When comparing most gas boilers to an average air source heat pump, the heat pump unit is usually between 3-5 times more efficient due to the lower flow temperature they work at.

Are New Radiators More Efficient Than Old Ones?

New radiators can be up to 50% more efficient than old ones. Part of this increased efficiency is thanks to improvements in technology. 

However, the majority of this efficiency gain comes from the fact that old radiators tend to have huge buildups of limescale (especially in hard water areas) and heating sludge (rust from the inside of pipework and radiators). This limescale and heating sludge stops radiators working at their maximum efficiency level.

A lot of people choose to have a power flush to rid their heating system of this problem. This isn’t advisable in old heating systems as it can put stress on soldered joints and lead to leaks. A more subdued chemical flush, or, simply replacing the radiators, is a much better option.

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