According to Andy Phillips, Chair of the Manufacturers’ Association of Radiators and Convectors (MARC), heating engineers need to be aware of the growing problem of so-called “illegal” radiators – products that fail to comply with the UK Construction Products Regulation (CPR) and the designated standard BS EN 442.

 “The performance figures used to size a heating system are only as good as the data behind them,” he says.  “If a radiator has not been tested correctly or its output has been overstated, the entire system design can be compromised.

 “We are delighted to be working with the Office for Product Safety and Standards (OPSS), to ensure that manufacturers and suppliers are providing information that is both accurate and compliant with BS EN 442.”

 Hydronic radiators, including steel panel radiators, designer radiators, multicolumn models and heated towel rails, must be independently tested to BS EN 442 before being placed on the UK market.  Every product must be supported by a Declaration of Performance (DoP), with heat outputs declared in Watts at both ΔT50 and ΔT30.  Advertising outputs at ΔT60 or higher is not permitted because it exaggerates radiator performance under normal UK operating conditions.

 For installers, identifying non-compliant products can be straightforward if they know what to look for.  Missing Declarations of Performance, heat outputs quoted only at ΔT60, outputs not expressed in Watts or an inability to provide evidence of independent testing should all raise concerns.

 These issues matter because accurate heat output data is fundamental to correct system design.  Since June 2022, Building Regulations have required new and replacement wet central heating systems to be designed for a maximum flow temperature of 55°C, supporting higher efficiency and making homes ready for low-carbon heating technologies.  Radiators must therefore be correctly sized to deliver sufficient heat at these lower temperatures.

 If installers specify radiators using inflated ΔT60 outputs, rooms may never achieve their design temperatures once the system is operating at 55°C or below.  The result can be longer running times, reduced boiler or heat pump efficiency, higher energy bills and dissatisfied customers.

 The consequences are particularly significant for heat pump installations.  Electricity remains substantially more expensive than gas, making efficient system design essential if homeowners are to achieve the expected running costs.  Incorrectly sized radiators can force heat pumps to operate at higher flow temperatures, reducing efficiency and undermining the very benefits low-carbon heating is intended to deliver.

 Although responsibility for regulatory compliance sits with manufacturers and suppliers, installers still carry significant commercial risk.  Poor system performance often leads to callbacks, replacement radiators, system redesign and warranty disputes, while the installer’s reputation is frequently the first casualty.

 MARC advises engineers to work only with reputable suppliers, always request the Declaration of Performance, check that outputs are quoted at ΔT50 and ΔT30, and carry out accurate room-by-room heat loss calculations before specifying emitters.  Combined with correctly balancing the finished system, these simple steps help ensure heating systems operate efficiently today while remaining ready for tomorrow’s low-temperature heating technologies.

 More information is available in the MARC guide, ‘Radiator Size Matters – Why the correct output is important for energy efficient heating systems’ [MARC-Energy-Efficient-Heating-Systems-v1-final-Aug-25.pdf]