Best radiators for heat pumps: how to choose and size

Posted by James Pickering on Tuesday 20th January 2026, updated on Tuesday 10th November 2026

White horizontal column radiator with chrome valves under a window, on a grey panelled wall beside a potted plant — Shown: Column radiators

Swap a gas boiler for a heat pump, keep every old radiator, and some rooms may never quite warm up. The radiators aren't broken. The water in them is just cooler than they were sized for.

So what are the best radiators for heat pumps? This guide shows you what to look for, and how much heat a radiator really gives at heat pump temperatures. You'll also see a worked example, a comparison of radiator types and what your installer should check.

Quick answer: There's no single best radiator for a heat pump. The best one is any radiator that gives out enough heat to cover the room's heat loss at the low water temperature your heat pump runs at. That often means a bigger radiator, or one with more panels, fins or columns. An installer certified by MCS (the Microgeneration Certification Scheme) works this out for each room.

Why heat pumps need bigger radiators

A heat pump sends cooler water round your radiators than a gas boiler does, so each radiator gives out less heat.

The Energy Saving Trust says a boiler typically runs at 75°C, while 45°C is usual for a heat pump. Heat pumps work more efficiently below 50°C or 45°C, says the radiator maker Myson.

That's the reason not to just turn the heat pump up. "The lower the flow temperature, the more efficient the heat pump, and the cheaper it costs you to run," says the Energy Saving Trust. So the radiators are sized to suit the cooler water.

The water temperature also moves with the weather. Many heat pumps follow a "heating curve", also called outdoor weather compensation. That means warmer water when it's colder outside, and cooler water when it's mild.

The Trust says your installer should set the curve when the heat pump goes in. A curve that isn't set correctly can raise your running costs. MCS's design standard has your installer give you the design flow temperature, which is the temperature of the water leaving the heat pump. Your radiators are sized for it.

Why do heat pump radiators feel cooler than gas boiler radiators?

Because the water inside them is cooler. A well-sized radiator on a heat pump feels warm rather than hot, and it still heats the room because it's big enough.

Heat pumps also suit a different routine. The Trust advises keeping a heat pump on for long periods, with a slightly lower "set-back" temperature when you're out or asleep. It also warns that a lower flow temperature means the house takes longer to warm up in cold weather.

Delta T: how much heat a radiator gives at heat pump temperatures

Radiator outputs are usually quoted at "ΔT50" (Delta T 50). That means water averaging 50°C hotter than the room: 75°C going in and 65°C coming out, in a room at 20°C. The radiator maker Stelrad calls this the UK's industry standard.

Cooler water means a smaller gap, and the heat falls faster than the gap does. Halve the gap from ΔT50 to ΔT25 and a radiator gives out about 41% of its rated heat, not 50%. So you can't simply scale the rating down by the temperature.

Radiator makers publish correction factors for this. These come from K-Rad's panel radiator brochure:

Water in the radiator averages (room at 20°C)	ΔT	Correction factor	Heat you actually get	If heat fell in step with ΔT
70°C	50	1.000	100%	100%
60°C	40	0.748	75%	80%
50°C	30	0.515	52%	60%
45°C	25	0.406	41%	50%
40°C	20	0.304	30%	40%

Bar chart: a radiator gives 100% of its rating at ΔT50, 75% at ΔT40, 52% at ΔT30, 41% at ΔT25 and 30% at ΔT20, less than if heat fell in step with ΔT. The figures are in the table above. — Halve the temperature gap and you get well under half the heat.

You can use the factors in two ways, Stelrad explains on its correction factor page:

Multiply a radiator's ΔT50 output by the factor, to see what it gives at your temperature.
Divide the room's heat need by the factor, to find the ΔT50 output to shop for.

Stelrad's general factors are almost the same as K-Rad's, but each model differs slightly. So use the maker's own figures for the radiator you're looking at. And remember the water cools as it goes round, so the average in the radiator is lower than the temperature leaving the heat pump.

Worked example: will my radiator be big enough?

Say a heat-loss calculation shows a room needs 900 W on a cold day. To keep the sums simple, take the room at 20°C and water averaging 45°C (ΔT25). For example, 50°C goes into the radiator and 40°C comes out.

The type numbers count panels and convectors (the fins behind the panels). A Type 21 has two panels and one convector, a Type 22 has two of each, and a Type 33 has three of each.

The radiator you have now: a K-Rad Type 21, 600 x 1000mm, rated 1,415 W at ΔT50. That's plenty on a hot boiler. At ΔT25 it gives about 574 W (1,415 x 0.406). That's about 326 W short.
What to shop for: 900 W divided by 0.406 is about 2,217 W at ΔT50.
A Type 22, 600 x 1200mm, is rated 2,202 W. At ΔT25 that's about 894 W, just short.
A Type 33, 600 x 1000mm, such as Stelrad's Compact, is rated 2,389 W. Using Stelrad's own data for this model, it gives about 957 W at ΔT25, enough. It fits the same wall as the old radiator, but stands 180mm out from it on its brackets.

So a radiator that was more than big enough on a boiler covers only about two thirds of this room's need on a heat pump. Our radiator size guide works through a bigger example at four water temperatures.

Why every room needs its own sum

Agree each room's temperature with your installer before sizing the radiators. MCS gives minimum design temperatures: 21°C for living rooms, 18°C for bedrooms, kitchens, halls and landings, and 22°C for bathrooms. Your design may use higher temperatures.

A warmer room loses more heat, and leaves a smaller gap for the radiator to work with. So the numbers shift room by room, and a calculation for each room is the only safe way to know.

Radiator types compared at a lower temperature

For the same wall space, the radiator with more heating surface gives more heat. Here are seven radiators of about 600 x 1000mm, with the outputs, depths and weights their Plumbworld listings gave in October 2026 (two exceptions are marked). Their ΔT30 figure means water averaging 50°C in a 20°C room.

Radiator (about 600 x 1000mm)	Material	Body depth	Weight	Output at ΔT50	Output at ΔT30
Single panel, Type 11	Steel	56mm	17.64 kg	950 W	489 W
Double panel, Type 21	Steel	70mm†	Not listed	1,415 W	728 W
Double panel, Type 22	Steel	105mm	30.12 kg	1,835 W	945 W
Triple panel, Type 33	Steel	158mm (180mm from the wall)	52.5 kg	2,389 W	1,217 W*
Two-column	Steel	70mm	27.5 kg	1,015 W	529 W
Three-column	Steel	100mm	38.2 kg	1,283 W	659 W
Double panel, aluminium	Aluminium	74.5mm	15.25 kg	1,312 W	675 W

The panel radiators are K-Rad's Kompact range and Stelrad's Compact Type 33. The column radiators are Park Lane's Colosseum (600 x 1010mm). The aluminium one is K-Rad's Hamilton (580 x 994mm).

*Calculated from Stelrad's data sheet for this model. Its listing gave 1,230 W.

†From K-Rad's brochure, because the Type 21 listing gives no depth.

What the table shows:

Panels and convectors add the most heat. A Type 33 gives about two and a half times the heat of a Type 11 on the same wall. The catch is depth and weight.
A Type 22 adds about 30% over a Type 21 of the same height and width, and is about 35mm deeper.
Columns look classic but give less here. These column radiators give less heat than a Type 22 of the same size. You'd need a bigger one, or more columns.
This aluminium radiator is light and slim, at about half the weight of the Type 22. But it gives less heat than the Type 22 of a similar size.

These are single models, and other designs differ. Check the total projection from the wall, including brackets, before ordering. Also check each listing's output, then convert it to your water temperature.

Are aluminium radiators best for heat pumps?

Not necessarily. Material alone does not determine heat output. The radiator maker Stelrad says it "doesn't mean all aluminium radiators emit more heat than steel radiators, it will depend on size as well." The table above shows exactly that. So compare each model's output at your system's water temperature. Well-sized steel panel and column radiators work too.

Here's how aluminium compares:

Lighter: the aluminium radiator in the table weighs about half as much as the steel Type 22.
Quick to heat up, and quick to cool down. That matters less with a heat pump that runs for long spells.
Low water content, so there's less water to warm.
Costs more than steel, and dents more easily, Stelrad says.
Needs the right inhibitor. Eastbrook's instructions for its Malmesbury aluminium radiator ask for an inhibitor that suits aluminium, and rule out nitrate-based ones. Follow your radiator maker's instructions, and your installer will check this.

If you like the look and the light weight, browse our aluminium radiators and compare their outputs as you would any others. Our guide on how to choose a radiator compares steel, aluminium and cast iron.

What do heat pump radiators look like?

Usually much like any other radiator, only bigger. Ordinary panel and column radiators can suit a heat pump if their output is enough at the cooler water temperature. There are also low-temperature radiators designed for it, including fan-assisted models, the radiator maker Myson says.

"Bigger" doesn't have to mean wider, the Energy Saving Trust says. It means more surface area, such as a double or triple panel radiator. Ways to get more heat from a wall include:

More panels and convectors: going from a Type 11 or Type 21 to a Type 22 or Type 33 panel radiator.
More height: vertical radiators use tall, narrow walls.
More columns or more width: column radiators gain heat with each extra column.
Two radiators instead of one: add their outputs together, at your water temperature.

Tall copper-coloured vertical column radiator in a grey hallway, between a panelled door and a coat rack — A tall radiator adds heating surface without taking more wall width. Shown: Vertical radiators

Some listings say a radiator is "heat pump compatible" or suitable for heat pumps. Check it anyway: what counts is its output at your water temperature, against the room's heat loss.

Myson says low-temperature radiators without fans are typically larger. So plan the wall space early, and check the depth if a radiator sits behind a door or furniture. Keep radiators clear too, because furniture or long curtains in front of one hold back its heat.

What if a bigger radiator really won't fit? MCS's design standard notes that listed buildings and other limits may stop larger radiators being used. Ask your installer about the options for that room: a taller radiator, two radiators, a fan-assisted model (next section), or a design with a higher flow temperature. A higher flow temperature costs efficiency, so ask for the difference to be explained (see the FAQ below).

Fan convectors and underfloor heating: other low-temperature options

Radiators aren't the only way to get heat from a heat pump. Myson says modern panel radiators suit flow temperatures of 45°C and above. For system temperatures below 45°C, it suggests fan-assisted radiators or fan convectors, "provided that a power supply is available near the radiators." It says they can work with system temperatures as low as 35°C.

The fan helps a compact unit give out more heat from cooler water. If one needs new wiring, have a registered electrician do it.

Underfloor heating is the other natural match. The whole floor gives out heat, so the water can be much cooler. Warmup, which makes both wet and electric systems, says wet (hydronic) underfloor heating can warm a room with water at 30 to 40°C.

A common set-up is underfloor heating downstairs and radiators upstairs. The Energy Saving Trust says that can cost less to install and cause less disruption. But the upstairs radiators need to be the right size, often larger, for the lower flow temperature.

The right mix depends on your home, the space and your budget. Settle it with your installer at the design stage, not radiator by radiator.

Bathrooms and heated towel rails on a heat pump

A bathroom needs extra care. MCS's minimum design temperature is 22°C for a bathroom, compared with 21°C for a living room and 18°C for a bedroom. A warmer room needs more heat, and the water has less of a gap to the room.

A heated towel rail can give less heat than a panel radiator on the same wall. One 1200 x 500mm central heating towel radiator on our site lists 556 W at ΔT50 and 295 W at ΔT30. A single panel Type 11 of the same face area, 600 x 1000mm, lists 950 W at ΔT50 (table above). At ΔT30 the towel radiator gives about 53% of its ΔT50 rating (295 / 556), much like the panel radiators.

So a towel rail may cover only part of a bathroom's heat loss on a heat pump. Ask your installer to check the bathroom's figure. If the rail falls short, ask about a taller or wider one, a second radiator, or wet underfloor heating for that room. Compare each rail's listed output as you would for any other radiator, and convert it to your water temperature.

Can I keep my existing radiators?

Sometimes. New radiators aren't mandatory for a heat pump, says the Energy Saving Trust, but bigger ones "could hugely improve" how well it heats your home.

Radiators that were generously sized for their rooms may still cover the heat loss at the lower temperature. Small ones often won't. The only way to know is a room-by-room heat-loss calculation, compared with each radiator's output at your heat pump's design temperature.

A room that loses less heat needs less from its radiator. So better insulation or draught-proofing can bring a radiator you already have closer to enough. Your installer's calculation shows by how much.

When you get a quote for a heat pump, the installer should tell you if they recommend upgraded radiators, the Trust says. They'll factor this into the quote. Ask for the radiators to be listed in it, room by room, so nothing comes as a surprise later.

How can I tell if my radiators are too small?

Rooms that stay cool on cold days, with the heat pump working as it should, are the first sign. Another is needing the heat pump's heating boost often. The boost is an extra heater that adds energy in very cold weather.

The Energy Saving Trust says that using it regularly may mean your radiators are too small, or that the heating curve isn't set right. Tell your installer. Sludge, trapped air or a fault can give the same signs, so ask them to check those too.

How heat pump radiator sizing works

Leave the sizing to your installer. The Energy Saving Trust recommends a heat pump installer certified by MCS, and suggests getting quotes from at least three.

Under MCS's heat pump standard, the installer works out the heat loss of each room with a calculation to BS EN 12831. The heat pump is then chosen to provide at least 100% of that heat load. Comparing each room's figure with its radiator's output, at the water temperature the system is designed for, shows which radiators need upgrading. The heat pump and the radiators are designed together, not one after the other.

Don't skip the calculation to save money. If the radiators are too small, rooms stay cool, or the heat pump has to run hotter, which makes it dearer to run.

Safety: A heat pump is specialist work. Use an MCS-certified installer to design and fit it, including the heat-loss calculation and the radiator sizes. Use a qualified heating engineer to fit, move or add radiators. Gas work, such as installing, servicing or repairing a gas boiler or gas pipes, is a job for a Gas Safe registered engineer.

The Trust also says that if your heating has no water treatment and filter, you should consider fitting them as soon as possible. Sludge and dirt in radiators can cause problems that look like a heat pump fault. Our guide on how to check your radiators explains the signs, and our guide to power flushing before new radiators explains how to protect new ones.

What your installer should give you in writing

MCS requires written information before installation starts. These are the key details for choosing your radiators:

Each room's heat loss per square metre of floor. Ask also for the total in watts, which you need for the sizing calculation.
The type and size of each radiator (or other emitter) they plan to use.
The design emitter temperature. Ask which room sets this temperature and why.
The design flow temperature, which is the temperature of the water leaving the heat pump.
The system's estimated seasonal efficiency at that flow temperature, with an explanation of what the figure means.

Boiler Upgrade Scheme grants in England and Wales

Through the Boiler Upgrade Scheme, eligible homes in England and Wales can get £7,500 towards an air source (air-to-water) or ground source heat pump, as of November 2026. The scheme isn't open in Scotland or Northern Ireland.

You don't apply yourself. The government's guidance says to get quotes from MCS-certified installers, and the installer applies on your behalf. The grant is then taken off what you pay, and shown on your quote and invoice.

Replacing a radiator before you get a heat pump

Planning a heat pump in a few years? If a radiator needs replacing now, ask an MCS-certified heat pump installer to size the new one for the planned lower water temperature. Then it's less likely to need changing again.

It can help now, too. Bigger radiators let your heating run with cooler water. And condensing boilers are more efficient when the water coming back to them is cooler, the Energy Saving Trust says.

Plan the wall space at the same time. A Type 22 or Type 33, a taller radiator or a second radiator may be the way to fit the output in.

Building or renovating? Then you can plan for cooler water from the start. Ask the designer to size every radiator for it, and to consider underfloor heating on the ground floor.

Tall dark grey vertical radiator with five flat tubes on a white living room wall, between a grey sofa and a TV unit — Short of wall width? A tall radiator can fit the extra output on a narrow wall. Shown: Aluminium radiators

Heat pump radiator FAQs

Do I need bigger radiators for a heat pump?

Often, but not always. Each radiator has to cover its room's heat loss at the heat pump's lower water temperature. At ΔT25, a radiator gives about 41% of its ΔT50 rating, so many rooms need a larger radiator or one with more panels. Your installer checks each room.

What are the best radiators for a heat pump?

There's no single best one. The best radiator is one whose output at your heat pump's water temperature covers the room's heat loss, and that fits the wall.

A Type 22 or Type 33 panel gives a lot of heat for its wall space, if you have room for the depth. Column, vertical and aluminium radiators can all work if their output is enough. The table above compares real models.

What are the best radiators for an air source heat pump?

Use the same test for an air source heat pump (ASHP): each radiator must cover its room's heat loss at the planned water temperature. Compare the types in the table above.

What size radiator do I need for a heat pump?

One big enough for the room's heat loss at your water temperature. Take the room's heat need in watts from your installer's calculation. Subtract the room's design temperature from the average radiator water temperature to find ΔT. Divide the room's heat need by the maker's correction factor for that ΔT. That gives the ΔT50 output to shop for, as in the worked example.

With water averaging 45°C and a room at 20°C, ΔT is 25. K-Rad's factor is 0.406, so the required ΔT50 rating is about two and a half times the room's heat need. Use the correct factor for your room temperature and radiator.

Is a Type 22 better than a Type 21 for a heat pump?

A Type 22 gives about 30% more heat than a Type 21 of the same height and width. In K-Rad's 600 x 1000mm range that's 1,835 W against 1,415 W at ΔT50, and 945 W against 728 W at ΔT30. It's also about 35mm deeper.

If the wall can take the depth, a Type 22 helps cover cooler water. A Type 21 may do in a room that loses less heat. Check the output at your water temperature either way. Our guide to single vs double panel radiators compares them in more detail.

Are oversized radiators for a heat pump a waste?

No. A radiator that looks oversized next to the room's need at ΔT50 may be just right at a heat pump's lower temperature. If it gives a bit more heat than needed, a thermostatic radiator valve senses the room's temperature and turns the flow down.

Can I run the heat pump hotter instead of changing radiators?

A higher flow temperature makes a heat pump less efficient and dearer to run. Radiators sized for the cooler water let it run that way. Ask your installer whether your system could give enough heat at a higher temperature, and what it would cost.

MCS's design standard says that where a design proposes a flow temperature above 55°C, an alternative design at 55°C or lower should also be provided. The differences in efficiency and energy use are explained to you, so you can choose.

Size for the water, not the boiler

The best radiator for a heat pump isn't a special type or a special metal. It's one that gives enough heat at the cooler water your heat pump sends round. Get the room-by-room figures from your installer, convert each radiator's ΔT50 output, and pick the shape you like that covers the number.

Ready to compare? Browse our radiators and check each listing's output.

Related reading: