Do heat pumps work with radiators?

Yes, heat pumps can work with radiators, and you can often use your existing ones, but be careful as some may need adjustments or upgrades for optimal efficiency. If you’re thinking of switching an old gas boiler to a modern heat pump system for your home, you may be wondering if it will work with your existing radiators. In this blog we’ll look at heat pumps and radiators, how they work together, if you need planning permission to fit one and what to consider when upgrading heating systems or radiators to get the best performance, lower heating bills and running costs for your home.

How do heat pumps work and do you beed planning permission? 

Ground source heat pumps and air source heat pumps are an efficient and eco-friendly alternative to the way traditional heating systems operates like gas boilers. In basic terms they work by extracting warmth from the air, ground or water outside your home and passing through a heat exchanger then moving it inside to warm the property though radiators or underfloor heating pipework. There are different types of pumps, air-source, ground-source and water-source but they all work on the same basic principle: extracting warm air, not generating it.

For most homeowners installing a heat pump doesn’t require formal permission. However planning permissions do vary depending on where you live, what type of property you own and the size of the installation. For example if you live in a listed building or conservation area you may need permission. Always check with your local council before starting any installations.

If you live in Cornwall head to Cornwall council's heat pump planning permission page for all the details. You might also find our blog on renewable energy in Cornwall useful.

​Can you use existing radiators with new heat pumps? 

The short answer is, yes but It depends. Most pumps run at lower flow temperatures when compared to traditional gas boilers. Conventional radiators are designed to work with high flow temperatures, so whilst you may be able to us your existing radiators they might not be as effective with a heat pump.  
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Radiators in most homes are designed to operate at 60°C to 80°C but pumps operate best when water is heated to 35°C to 45°C. This lower temperature range allows the heat pump to achieve high energy efficiency levels. With this lower flow temperature, your radiators will still be warm and effectively heat your home but won’t feel as hot to the touch as they did with a traditional boiler.

Can heat pumps systems work with cast iron radiators? 

Cast iron radiators are known for retaining and radiating heat over a long period of time, which makes them perfect for traditional central heating systems. However with heat pumps cast iron radiators may not always be the best match, especially if they’re old or small. When using heat pumps with radiators they need to have a larger surface area to emit enough warmth. Many older cast iron radiators are too small to provide adequate warmth at these lower temperatures.

Cast iron radiators are slower to warm up and cool down compared to modern radiators made from steel or aluminium. Because heat pumps run at lower temperatures it may take too long for cast iron radiators to reach the desired temperature and they may not perform as well at keeping your home warm when its really cold outside.
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That said if your cast iron radiators are the right size and in good condition they can still work well with a heat pump system. Just be prepared for the system to take longer to warm up and you may need larger radiators to get enough warmth in bigger rooms.

​Best type of radiator to use with air source heat pumps

The best radiators to use with air source heat pumps (ASHP) are those specifically designed for low-temperature heating, which are designed to be lightweight, responsive, and efficient at lower temperatures. Heres a list of the best radiator types for ASHP.

Aluminium radiators – best overall
✅ Fast heat-up & cool-down – highly responsive, ideal for heat pumps.
✅ Excellent heat conduction – transfers warmth quickly and efficiently.
✅ Lightweight & stylish – easier to install and available in modern designs.

Steel panel radiators – great for most homes
✅ Good heat output – panel radiators work well with low temperatures when sized correctly.
✅ More affordable than aluminium – a good balance of cost and performance.
✅ Variety of sizes available – can be sized up to compensate for lower temperatures.

Low-temperature radiators – specifically designed heat pump radiators
✅ Larger surface area – maximises heat distribution at lower temperatures.
✅ Optimised for efficiency – uses built-in fans or increased panel size to boost heat output.
✅ Ideal for retrofitting – designed to work seamlessly with ASHPs.

Cast iron radiators – only use if big enough
⚠️ Slower heat response – takes longer to warm up and cool down.
⚠️ Higher water volume – requires the pump to work harder.
✅ Good for well-insulated homes – if sized correctly, they can work efficiently. ​

Best radiator alternative: underfloor heating
If possible, underfloor heating is the most efficient option to generate warmth, as it produces high heat outputs evenly at very low temperatures.

What to do if your existing radiators aren’t compatible?

If your current radiators are not compatible with your modern heat pump installation you have a few options. It may be time for radiator replacements, you can upgrade your radiators to bigger ones designed for low flow temperature heating. By fitting larger radiators you can increase the surface area and improve heat distribution throughout your home.

​Another option is to switch to underfloor heating which is highly compatible with heat pumps as it distributes heat more evenly and at lower temperatures. If you’re renovating or building a new home incorporating underfloor heating can be a great way to ensure your heat pump operates with maximum efficiency.

How to tell if your radiators will work with an air source heat pump?

The key factor in determining if your existing radiators will work with air source heat pump technology is their size and material. Larger radiators with more surface area will perform better with low temperature heating. The material of the radiator matters as well, modern radiators made from materials like aluminium or steel are more responsive and efficient than older cast iron models.

Tip - Check your home’s insulation
If your home is well insulated you may not need big radiators to feel comfortable as the warmth will be retained better. Seek professional advice from a trained heating engineer who can assess your existing radiators, the type of air source heat pump you’re considering and your home’s overall energy needs to give you a clearer picture if your current setup will be enough.

Conclusion

Heat pumps can be a great addition to your home heating system, they reduce carbon emissions and are a great eco-friendly alternative to traditional gas boilers that use fossil fuels. While you can use your existing radiators with a heat pump ensuring they are the right size and material is essential to get the most out of your investment. If your current radiators are not suitable for modern systems upgrading to larger or more modern ones will ensure your new pump system operates efficiently and keeps your home warm. KozyKoala are local heating installers in Cornwall, get in touch to discuss your next renewable energy upgrade.

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