Despite action by regulators and industry groups such as The Manufacturers’ Association of Radiators and Convectors (MARC), the issue of misleading Delta T figures on radiators still persists.
The effectiveness of any heating system depends heavily on matching the radiators to the heating demands of the space. Accurate selection is only possible when radiator outputs are based on the appropriate Delta T value to ensure the specified heat output reflects real operating conditions.
Undersized or oversized radiators can cause uncomfortable indoor temperatures, increased energy consumption and reduced efficiency. In many cases, specification errors can be traced back to the Delta T values used to calculate radiator outputs.
The Delta T is the difference between the average water temperature in the heating system and the target ambient room temperature. The greater the Delta T, the hotter the radiator surface will be and the more heat it will produce. If this figure is incorrect when specifying a radiator, then your calculation for sizing the radiator will not be correct.
Where the issues lie
The Construction Products Regulation 2011 places a legal obligation on manufacturers, including importers, distributers and resellers, to provide verified information about a product’s thermal performance. To comply, every hydronic radiator, including heated towel rails, must be tested independently in accordance with BS-EN 442 standards by an accredited independent laboratory. The test results must then be documented in a Declaration of Performance (DoP), which specifies the radiator’s heat output in Watts at both Delta T50 and Delta T30. Delta T50 is the recognised standard rating for radiator performance, while Delta T30 is used to assess suitability for lower temperature systems.
However, some manufacturers and resellers state outputs in their materials and documents, or on their website, that are based on Delta T 60 or greater – which assumes higher system water temperatures. As a result, heating professionals will receive an exaggerated idea of the radiator’s output, meaning that if they use this as the basis of their heating calculations, the radiators will be undersized, leading to higher energy consumption and bills for customers.
This may also impact the customer’s confidence in modern heating systems, including heat pumps, since their heat outputs are even more critical because of their lower operating temperatures.
What you need to know
To avoid system performance issues, installers should only use products sourced from manufacturers who can provide independently verified product testing to back up the performance data.
Under both UK and EU law, manufacturers must supply a Declaration of Performance for each radiator if requested in either paper or electronic forms. This should also contain details of the organisation that carried out the tests, including verification from notified bodies.
Suppliers should also look out for a membership of MARC in the DoP, as this is a good indication of reliability and credibility. MARC is working with the Office for Product Safety and Standards, the body that enforces the Construction Products Regulations, to stop manufacturers providing misleading performance values.
MARC has also been raising awareness around the issue to ensure specifiers and customers understand the problem so that they can make well informed decisions. As a member of MARC, The Radiator Company is committed to supporting the organisation’s efforts to increase awareness of this important issue. www.theradiatorcompany.co.uk
Andrew Phillips is Managing Director at IRSAP and Chairman of MARC.