Radiator standard BSEN442


1st JULY 1997 - April 2000


Up until July 1997 the Radiator Standard within the UK was BS 3528. It was introduced over 20 years ago and testing facilities also dated back to that time. Technology has moved on in both manufacturing and testing and the time is right for a European-wide, updated standard.




Up until now, radiators sold in Europe have had to meet standards set by each individual country's certification body. In some countries there has been a legal framework to standardised certification, BSI in the UK or DIN in Germany for example, whilst in others only minimal commercially based quality schemes have been applied.


With different test institutes and certification bodies, significant differences have sometimes occurred in the heat output of the same radiator in different markets. At the same time, there have been varying pressure testing requirements, product quality and material specifications, some complying with the requirements of the European Construction Products Directive, whilst others do not.

Standardised certification of radiators

From an initial French request, a Technical Committee made up of representatives from the 18 National Standards bodies, test institutes and user associations was established to draft a new European Standard. Such a Standard has to comply with an agreed framework , taking into account such topics as safety in use, marketing and labelling, manufacturing quality and performance rating.

Some of these were included in the old UK Standard, others inadequately or not at all.

Heat output performance is obviously the main requirement for radiators but there are several other important aspects covered by the new Standard which were either not covered by BS3528 or are now covered with greater precision:

  • Minimum material thickness for all wet surfaces
  • A detailed table of manufacturing tolerances
  • Periodic burst pressure tests to supplement the 100% leak pressure tests
  • Pre-treatment and paint quality requirements for corrosion protection and resistance to impact damage
  • Requirements for product marking, labelling and catalogue data

It is in the area of heat output performance, however, that the new Standard will have the greatest immediate impact.

1997 Outputs reduced by 11% in the UK Why?

Because the test methods, accuracy of testing and design of the new test rooms were changed from the previous BS 3528 test criteria. The Technical Committee drew up a very tight specification for a new standardised test room which, coupled with changes to test methods and rating procedures, resulted in remarkable accurate and consistent results. There are currently four such test rooms, at BSRIA in Bracknell England, at Lyon, Stuttgart and Milan. These have reported repeatable results with an accuracy of +/-1%. Radiators tested under the new Standard are tested at a lower temperature difference than under old national standards.



Flow C
Return C
Air Temp C
Delta T
BS 3528
BS EN442
This Delta T, the difference between the mean water temperature in the radiator and ambient air temperature in the test chambers, was previously Delta T 60 degrees C, now it is 50 degrees C. While this may not sound significant, outputs at Delta T 50 is over 20% lower than at Delta T 60. However, it's rather like testing fuel consumption of a car at 60mph instead of 50mph. Fuel consumption drops, but only because a different reference point has been taken.

UK installers have been used to brochure outputs derived at Delta T 60, so to prevent confusion, particularly during the introductory phase of the new Standard, manufacturers catalogues continued to show Delta T 60 outputs for the full spread of radiator models, with only the headline reference to the nominal outputs at Delta T 50. This means that the tested radiators at Delta T 50 were corrected back up to Delta T 60 output figures. (see paper on correction factors)

Reference to the headline figure is interesting; the four test centres could not possibly test all radiator models for all brands within such a short period of time, so a grace period of two years was allowed for manufacturers to test all models within their ranges. Until then one-meter long radiators from each height available in the range, were tested as a reference point. These reference points were used to calculate the outputs of the remaining radiators in the range!

Other changes included testing with Top Bottom Same End (TBSE) connections rather than the old, Top Bottom Opposite End (TBOE). The new design of test room, particularly the elimination of water cooling to the rear wall of the test booth itself, resulted in outputs that are lower, regardless of the Delta T used.

April 2000 radiator outputs change again

April 2000 ends the grace period that was allowed for manufacturers to test individual radiators. Because of the vagaries of using 'reference test figures' the true outputs now being published are in some cases lower and others higher than previously reported. Some manufacturers have altered the product to optimise performance from the new test criteria, again resulting in differing outputs.

As always the Installer/Design engineer can only work on the data provided by the manufacturer at any point in time, always make sure you are working from the most up to date manufacturer catalogue. Catalogue outputs are test outputs only and need to be corrected by the designer to get the true radiator output figure, taking into account installation differences in flow rates and room temperature.

The key feature of the test methods is the accuracy and consistency, which is now being achieved. After the initial transitional period, gone is the absurd situation in which the same radiator could be sold in the UK, Benelux, France or Germany at four different outputs.

The consistency of the results allows greater confidence and precision at every stage of the specification process, coupled with the close manufacturing tolerances and quality requirements, the new Standard will give the specifier greater confidence in the sizing of radiators, besides offering full compliance with the Construction Products Directive.