Best radiators for heat pumps

If you are moving to a heat pump, the radiators matter more than most people expect. A heat pump heats your home very differently from a gas boiler, and radiators that were fine on the old system can leave rooms cold on the new one. The reason is simple once you see it: heat pumps run cooler, so each radiator gives out less, which means you generally need bigger or higher-output radiators. This guide explains why, how much difference it makes, why aluminium suits heat pumps, and how sizing works, so you go into the switch with the right radiators planned in.

Why heat pumps need different radiators

It comes down to flow temperature. A gas boiler sends hot water to the radiators, traditionally around seventy degrees or more. A heat pump is most efficient running much cooler, often somewhere around forty to fifty degrees depending on the system and the weather. A radiator gives out heat in proportion to how much hotter it is than the room, so the same radiator running on cooler water puts out far less heat, sometimes little more than half its boiler-era figure. To deliver the heat a room needs from that cooler water, you need a radiator with a much higher rated output, which in practice means a larger or higher-output radiator than a boiler system used.

This is why simply swapping the boiler for a heat pump and keeping the existing radiators often disappoints: the radiators were sized for hot water and cannot deliver enough heat when the water is cooler. A good heat-pump installation looks at the radiators room by room, not just the heat source. The same logic is why a heat pump is rarely a like-for-like swap done in an afternoon: the heat source and the heat emitters have to be designed together to work at the low temperature, and the radiators are as much a part of that design as the unit outside.

There is an efficiency reason to embrace the lower temperature rather than fight it. A heat pump works harder, and uses more electricity, the hotter you ask it to run, so cranking the flow temperature up to suit old radiators undermines the very efficiency you fitted it for. Sizing the radiators to deliver the heat at a low flow temperature lets the heat pump run gently and cheaply. So upsizing radiators is not just about comfort; it is what lets the system run efficiently, which is the whole point of a heat pump.

Output and oversizing

The headline output figure on a radiator assumes a particular temperature difference between the radiator and the room, commonly quoted at delta T 50, which reflects a fairly hot system. Run the radiator cooler, as a heat pump does, and the real output drops well below that figure. So when you size for a heat pump, you cannot take the delta T 50 number at face value; you size for the lower temperature your heat pump actually runs at, which means choosing radiators rated well above the room's bare requirement so they still deliver enough once the cooler water is taken into account.

In practice this means bigger radiators: taller, wider, double-panel, or more columns, anything that adds heated surface area. Some rooms may need a larger radiator than the wall easily takes, which is where slim-but-high-output options and careful placement come in, or occasionally two radiators sharing the load. The key idea is that oversizing on a heat pump is not waste; it is how you get the heat out at a low, efficient flow temperature.

It helps to think of it as matching the radiator to the temperature, not the other way round. On a boiler you could undersize a radiator and just turn the flow up to compensate; on a heat pump you keep the flow low for efficiency and make the radiator big enough to suit. That reframes what a good heat-pump radiator looks like: not the smallest one that fits, but one comfortably rated above the room's bare need so it still delivers when the water is only mildly warm. Installers often work to a target flow temperature and size every radiator to hit each room's heat loss at that temperature, which is why the schedule of radiators for a heat pump reads larger throughout than a boiler equivalent.

Why aluminium suits heat pumps

Aluminium is the material that makes low-temperature heating easier. It gives high output for its size, so it helps deliver the heat a room needs without covering the whole wall, and it heats and cools quickly, so it responds well to the steady, lower-temperature running a heat pump favours. It also holds little water, so there is less to warm. Put together, those traits mean an aluminium radiator can often hit the required output at a heat pump's flow temperature in a more manageable size than a heavy steel or cast-iron radiator would. It is not the only option, well-sized steel panels and columns work too, but aluminium is the material most suited to the job. It is also light, which makes the larger sizes a heat pump calls for easier to handle and fix than heavy steel or cast iron at the same output, and it pairs naturally with the steady, low-temperature running a heat pump favours.

Aluminium radiators are the natural starting point for a heat pump; high-output column radiators can also deliver the surface area larger rooms need.

Sizing for a heat pump

Sizing for a heat pump is a proper heat-loss exercise, not a rule of thumb, and it is best done by your installer as part of the system design. They calculate each room's heat loss, decide the flow temperature the heat pump will run at, and size each radiator to deliver that room's heat at that temperature, which is why the radiators come out larger than on a boiler system. As a homeowner, the useful things to know are: expect some or all radiators to be upsized; plan wall space for larger or taller radiators; consider aluminium for its output and response; and treat the radiators as part of the heat-pump project from the start, not an afterthought. Getting this right is the difference between a heat pump that keeps you warm efficiently and one that struggles.

One more practical point: do not be tempted to skip the assessment to save money up front. An undersized radiator on a heat pump does not just feel cooler; it forces the whole system to run hotter or longer to compensate, eroding the efficiency and running-cost savings the heat pump was fitted for. The radiators are a relatively small part of the overall project cost, and getting them right protects the much larger investment in the heat pump itself. Treat the room-by-room sizing as essential, not optional.

For the underlying method, see what size radiator do I need?, and follow your installer's room-by-room heat-loss calculation and any MCS guidance for the detailed figures (BTU guide linking when live).

What about underfloor heating and fan convectors?

Radiators are not the only way to get heat out of a heat pump at a low temperature, and it is worth knowing the alternatives. Underfloor heating is a natural partner for a heat pump: it spreads warmth across a large surface, the whole floor, so it delivers plenty of heat at a low temperature without any visible radiator, which is why new builds and major renovations often pair the two. Fan-assisted convectors are another option: they use a quiet fan to blow air across a low-temperature heat exchanger, getting more heat out of cooler water in a compact unit, useful where a big enough radiator will not fit. For most retrofits, though, suitably sized radiators remain the simplest and cheapest route, often alongside underfloor heating downstairs. The right mix depends on the property, the available space and the budget, and is settled as part of the overall system design rather than chosen radiator by radiator in isolation, so it pays to discuss the whole heating approach with your installer early on, at the design stage.

Planning the switch

If a heat pump is on the horizon, the radiators are worth thinking about early, even if the switch is a way off. When you replace a radiator now on your existing boiler, choosing a generously sized or high-output model, or aluminium, can mean it is already heat-pump-ready, saving you changing it again later. When the heat-pump design is done, your installer will tell you which rooms need upsized radiators; budget for those as part of the project rather than a surprise. And plan the wall space, since heat-pump radiators are often larger, so a tall vertical or a double panel may be the way to fit the output in. Treating the radiators as part of the heat-pump plan from the outset avoids cold rooms and rushed compromises later.

Building or renovating gives you the freedom to size everything for low-temperature running from the start: combine well-sized aluminium radiators with underfloor heating where it suits.

Heat-pump radiator FAQs

Do I need to change my radiators for a heat pump?

Often some or all of them, yes. Heat pumps run at lower temperatures, so radiators give out less heat and many need to be larger or higher-output to keep rooms warm. Your installer assesses each room; some existing radiators may be fine, but expect several to be upsized.

What are the best radiators for a heat pump?

Higher-output radiators that deliver the heat a room needs at a low flow temperature. Aluminium is the leading choice for its high output, fast response and low water content, with oversized panels and column radiators also working well.

Why do heat-pump radiators need to be bigger?

Because the water is cooler. A radiator gives out heat in proportion to how much hotter it is than the room, so on a heat pump's lower flow temperature it puts out less than it would on a hot boiler system. A larger radiator with more surface area makes up the difference at that lower temperature.

Can I keep any of my existing radiators?

Sometimes. Radiators that were already generously sized for their rooms may still deliver enough at the lower temperature, while undersized ones will not. The only way to know is a room-by-room heat-loss assessment, which your heat-pump installer carries out as part of designing the system.

Is aluminium essential for a heat pump?

No, but it helps. Well-sized steel panels and columns also work, and the real requirement is enough output at the low flow temperature. Aluminium simply makes that easier to achieve in a sensible size, thanks to its high output and quick response.

Why does running a heat pump hotter reduce efficiency?

A heat pump uses more electricity the bigger the gap between the outside air and the water temperature it produces, so the hotter you run it, the harder it works and the more it costs. Sizing radiators to deliver enough heat at a low flow temperature lets the heat pump run cool and efficiently, which is exactly why heat-pump radiators are upsized rather than run hot.

Shop aluminium radiators for low-temperature heating, or read what size radiator do I need? to understand the sizing (linking when live). Trusted since 1999, with free UK delivery and 365-day returns. Big brands, small prices.

This guide is general information. Heat-pump radiator sizing should be carried out by a qualified installer as part of the system design.