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What size panel radiator do I need

Updated: 22 October 2026

You are holding a tape measure, or a BTU figure from an amazon.co.uk listing, and neither tells you whether the radiator will hold a UK room at the flow temperature you actually run. What size panel radiator do I need starts with the room, then Delta T for wet steel, then a watt label for electric. Square-metre claims are a different language. Printed outputs for the ten listings are in the [panel radiators comparison](/hub/heating/panel-radiators). Peter F. checked those listings and public UK sources. There was no lab test. A qualifying purchase can earn a commission at no extra cost to you.

You are holding a tape measure, or a BTU figure from an amazon.co.uk listing, and neither tells you whether the radiator will hold a UK room at the flow temperature you actually run.

Our top picks

NRG NRG 1600x408 mm vertical single

Best overall

NRG NRG 1600x408 mm vertical single
9.4/10about £97.95
View offer
Devola Devola DVPW2000B

Rank 2

Devola Devola DVPW2000B
9.2/10about £139.95
View offer
Devola Devola DVS2000W

Best value

Devola Devola DVS2000W
9.0/10about £99.95
View offer
On this page
  1. 1.Measure the room before the radiator
  2. 2.Read Delta T before you compare BTU
  3. 3.Electric coverage lines are not BTU
  4. 4.When the number is not on the listing

Measure the room before the radiator

Start with length, width and ceiling height in metres, then note what the walls lose heat to. An outside wall, a large window, or a room over a garage changes the number more than an internal box room. Retailer calculators return a BTU band at ΔT50. That is a rule of thumb, not a survey. A living-room band of 5,000–9,000 BTU is often quoted for typical insulation. Floor-to-ceiling glass is not typical. Write down the face you can fit: width, height under a sill, and depth if the walkway is tight. A 1200 mm type 22 replaced by a 600 mm single underheats. For electric, note where a 1.5 m or 1.4 m cable reaches a socket without an extension lead.

Read Delta T before you compare BTU

Catalogue radiators are tested under BS EN 442-2. Manufacturers should quote output at ΔT50 and, for lower flow, at ΔT30. Delta T is the difference between mean water temperature and room air. ΔT50 means mean water at 75°C and a room at 20°C. If a new or fully replaced wet system in England is designed for a 55°C maximum flow, from 15 June 2022, the useful column is often ΔT30. The higher label on a cooler system makes the emitter look stronger than it will behave. Use 1 W ≈ 3.412 BTU/h only to compare units. Electric watts are input. Wet BTU at a named Delta T is tested water output. The NRG vertical prints 2484–3139 BTU with no Delta T. You cannot split that band into ΔT50 and ΔT30 from the listing. Ask for a Declaration of Performance, or use a calculator instead of the middle of the range.
NRG NRG 1600x408 mm vertical single

Testsieger

NRG NRG 1600x408 mm vertical single
9.4/10about £97.95
View offer

Electric coverage lines are not BTU

Plug-in panels quote areas that are not heat-loss maths. The Devola DVS2000W and DVPW2000B claim 22 m². The DVPW1500WH claims 20 m². The TCP claims 250 square feet, the MYLEK charcoal panel 240 square feet, and a MYLEK ceramic 150 square feet. Those are seller fields, not BS EN 442 tests. A 2000 W panel at full output delivers 2000 W, whatever the bullet says. Compare that label with your calculator figure, and derate if insulation is poor. At 26.32 pence per kWh on the Ofgem cap for 1 October to 31 December 2026, one hour at 2000 W is about 52.6 pence before the standing charge. A thermostat can shorten the time at full power. It does not change the draw while the element is on.

When the number is not on the listing

Stop DIY sizing for an open stair, a heat-pump retrofit, or several rooms that were always cold. A heating engineer can pick ΔT30 rows. Gas Safe matters if the gas appliance is opened. If the electric loss exceeds 2000 W, one panel underheats unless you add a second heater. If the NRG range has no Delta T, do not assume either end of 2484–3139 BTU. Once you have a target at the right column, best panel radiator maps the job to a listing.

Common questions

Do I size from the old radiator’s width?
Use the old width as a clue, not a rule. Type and depth matter as much as width. A narrower single on the same pipes often delivers less heat than an old double. A tall single can underheat a room that had a type 22, even when the new radiator looks larger.
What is Delta T 50 in plain words?
It is the test condition where the water is much hotter than the room, used to compare catalogue radiators. ΔT50 means mean water at 75°C and room air at 20°C. It is not the flow temperature your heat pump will run every day.
Why does a heat pump need a larger panel?
A lower flow temperature reduces output at the same physical size. In England, a new or fully replaced wet system is sized for a 55°C maximum flow where practicable, from 15 June 2022. You read the ΔT30 column, not the ΔT50 headline, when that design applies.
How do I turn BTU per hour into watts?
Divide BTU/h by 3.412, or multiply watts by 3.412 to get BTU/h. Use that only after you are comparing like-for-like conditions. Electric watts are input. Wet BTU at a named Delta T is tested water output. The conversion does not make them the same product.
Can I trust a claim that a panel heats 22 square metres?
Not as a calculation. The Devola 2000 W panels print 22 m², and the 1500 W glass panel prints 20 m². Treat those as seller lines. Measure the room and use a calculator band instead.
What measurements do I need before I use a calculator?
Room length, width and ceiling height, outside wall length, window area, the floor type below, and the design temperature you want. For a wet panel, know whether you are sizing at ΔT50 or ΔT30 for your flow. For electric, note the socket the cable can reach without an extension lead.
When is a calculator not enough?
When you have an extension, a heat-pump retrofit, an open stair, or a whole home that never held temperature with the boiler running. A heating engineer can run a heat-loss design. Gas Safe matters if the gas appliance itself is opened.
What do I do with a BTU range that does not name Delta T?
Do not split it into ΔT50 and ΔT30 yourself. The NRG listing prints 2484–3139 BTU and does not name Delta T, so that range is not those two test points. Request the documentation, or pick a listing that states both.

Related pages

Panel radiator buying guide

Electric panel heater vs central heating

Panel radiators

Bathroom panel heater: UK zones, IP24 and the plug

Best panel radiator: wet pipes, timer or Wi-Fi glass

Sources

Public UK sources named below. amazon.co.uk prices, stars and review counts on these ten listings were taken from the listing files read on 20 October 2026. Page updated October 2026.

  1. Screwfix radiator buying guide (retrieved 20 October 2026)
  2. HHIC on BS EN 442 (retrieved 20 October 2026)
  3. BSI, BS EN 442-2:2014 (retrieved 20 October 2026)
  4. legislation.gov.uk, Regulation (EU) 2015/1188 (retrieved 20 October 2026)
  5. BEAMA Part L heating controls note (retrieved 20 October 2026)
  6. SELECT bathroom zones pocket guide (retrieved 20 October 2026)
  7. Electrical Safety First, bathrooms (retrieved 20 October 2026)
  8. Ofgem price cap unit rates (retrieved 20 October 2026)