Understanding EN 442: What ΔT50 and ΔT30 Outputs Really Mean for Buyers
Every radiator legally sold in the European Union carries a declared heat output measured under EN 442. Yet in B2B procurement we regularly see tenders comparing figures that were never comparable: outputs at different temperature regimes, ratings without a stated ΔT, or catalogue numbers with no test report behind them. This guide explains what the standard actually measures and what a buyer should check before signing a supply contract.
What EN 442 covers
EN 442 is the harmonised European standard for radiators and convectors operating below 120 °C. Part 1 defines technical specifications and requirements — materials, pressure tightness, surface treatment, marking. Part 2 defines the test method for thermal output: the radiator is measured in a closed, water-cooled booth at a notified laboratory, at a standard regime of 75 °C flow, 65 °C return and 20 °C room air. Because the standard is harmonised under the Construction Products Regulation, a radiator placed on the EU market must carry CE marking with a declaration of performance based on these tests.
ΔT50 in plain terms
The headline figure from an EN 442 test is the output at ΔT50. The ΔT — also called excess temperature — is the difference between the mean water temperature and the room air: (75 + 65) / 2 − 20 = 50 K. So when a datasheet says "1 460 W", it means 1 460 W when the water inside the radiator averages 70 °C in a 20 °C room. If your system runs cooler — and most modern systems do — the real output will be lower. This single fact explains most "underperforming radiator" complaints we encounter in projects.
The characteristic equation and the exponent n
An EN 442 test does not produce one number but a curve, described by the characteristic equation Φ = Km × ΔT^n. Km is a constant for the model; the exponent n describes how steeply output falls as the water cools. For steel panel and tubular radiators n is typically close to 1.3. The test report states both values, which lets an engineer compute output at any regime — not just the two printed in a catalogue. When comparing suppliers, ask for Km and n: two radiators with identical ΔT50 ratings but different exponents will behave differently in a low-temperature system.
Why ΔT30 has become the second headline figure
With heat pumps and condensing boilers, design water temperatures have dropped to 40–55 °C, which corresponds to ΔT of roughly 25–35 K. At ΔT30 a steel radiator delivers about 51% of its ΔT50 rating (0.6^1.3 ≈ 0.515). Markets that are electrifying heating — Spain, France, the UK — increasingly expect both figures side by side. JIUDING product pages show ΔT50 and ΔT30 outputs for every series, so specifiers do not need to redo the conversion.
How to read a test report: a buyer's checklist
When qualifying a radiator supplier, request the EN 442 test reports and check five things. One: the issuing laboratory — it should be a recognised notified body (JIUDING's thermal performance is validated by BSRIA in the UK, which also covers UKCA compliance). Two: that the tested models and sizes actually cover the range you are buying — interpolation between tested sizes is legitimate, extrapolation beyond them is not. Three: the presence of Km and n values, not just a single wattage. Four: consistency between the report, the declaration of performance and the catalogue. Five: pressure data — EN 442 also requires tightness; JIUDING additionally pressure-tests every production unit at 1.5× working pressure as part of ISO 9001 process control.
Red flags in supplier documentation
Outputs quoted without any ΔT reference. Catalogue figures that exceed the test report for the same size. "Equivalent to EN 442" wording without an actual report. A single test certificate recycled across visibly different product generations. None of these automatically mean bad product — but each is a reason to ask further questions before committing volume.
Where to verify our documentation
JIUDING manufactures steel panel, column, designer and towel radiators with an annual capacity of 4 million sections across 600+ specifications. Our EN 442 test reports, CE declarations and UKCA documentation are available in the documentation centre, with certificates summarised on the credentials page. For project-specific data — custom heights, colours or connection types — our engineering team provides per-model output tables on request.