Choosing a designer radiator

People choose a designer radiator for how it looks. It still has to keep the room warm. Whether it does depends on its heat output. The way that number is quoted needs a careful read.

How heat output is rated

A radiator's output is measured at a set difference between the room and the water inside it. The industry calls this difference Delta T, written ΔT.

Most outputs are published at ΔT50. That assumes a room at 20°C and water averaging 70°C, which is what a traditional gas boiler runs at.

The Manufacturers' Association of Radiators and Convectors says every radiator must come with a Declaration of Performance. It must give the output in watts at both ΔT50 and ΔT30. The association says quoting outputs at ΔT60 or higher breaches the Construction Products Regulation.

Radiators on a heat pump

A heat pump heats the water to a lower temperature, so the same radiator gives out less heat. At ΔT30, a typical heat-pump setting, a radiator gives roughly half its ΔT50 output.

One maker's three-section cast iron radiator shows it clearly. It is listed at 442 W at ΔT50 and 229 W at ΔT30.

So when you compare radiators for a heat pump, compare their ΔT30 outputs. The Energy Saving Trust lists radiator upgrades as one of the things that can affect the cost of fitting a heat pump.

In England and Wales, you can get £7,500 towards an air source or ground source heat pump from the Boiler Upgrade Scheme, if your home qualifies. GOV.UK sets out who can apply.

The 55°C rule for new heating systems

In England, the standard for a heating system that is newly installed or fully replaced is in Approved Document L. Its pipework and radiators should be sized so the system works at a flow temperature of 55°C or lower. There is an exception where there is not enough space for larger radiators.

A new edition of Approved Document L takes effect on 24 March 2027. It keeps the 55°C provision.

Radiator valves and the thermostat

Approved Document L allows more than one way of controlling the heating room by room. One is a room thermostat, with a thermostatic valve on each radiator in the other rooms. In that setup, it says not to fit a valve in the room with the thermostat.

Electric radiators and towel rails in a bathroom

Under Approved Document P, some electrical work must be notified to building control. That includes a new circuit, and any change to a circuit near a bath or shower. Near a bath or shower means within 0.6 metres of the edge of the bath or shower tray, and up to 2.25 metres high.

Since 2018, a fixed electric heater has had to meet an efficiency standard set by the Ecodesign rules. That is why most new electric radiators have an electronic thermostat and a weekly timer.

Running costs

Ofgem's price cap for 1 October to 31 December 2026 puts electricity at 26.32p per kWh on average, with no VAT until 31 March 2027. Gas is 7.97p per kWh, including VAT.

An electric radiator turns each kWh of electricity into a kWh of heat. So it costs about three times as much to run as a gas boiler giving the same heat. The cap changes on 1 January 2027.

Sending a radiator back

When you buy from a shop online, you usually have 14 days to cancel after the radiator is delivered. You normally pay the cost of sending it back, which can be a lot for a heavy radiator.

The right to cancel does not cover goods made to your specification. A radiator made to order in a colour or size you chose may fall into that group, so ask before you order.

Useful links