In addition, the flow and return connections should be connected at the same end, normally referred to as ‘top bottom same end’. Under BS EN 442, to calculate a Delta rating, radiators must be tested with a flow water temperature of 75☌ and a return temperature of 65☌ in a test room with a consistent air temperature of 20☌. Prior to 2013, the UK used Delta 60 until it opted to come into line with the rest of Europe. Delta 50 is now the UK standard for all domestic gas boiler systems. That output will usually either be expressed as a measurement taken either at Delta 60 (Δ T60) or Delta 50 (Δ T50). The wattage of a radiator is based on the system’s likely operating temperature. A radiator’s power output is most often expressed in watts. So, if the average water temperature across the radiator is 70 degrees C, the Delta T is 50 degrees C. The standard room temperature desired is usually quoted as 20 degrees C. When you look at a radiator’s specifications, you’ll find the heat output figure quoted is the unit’s Delta T at a specific room temperature. What is average radiator water temperature? Well, if you have an input of 80 degrees and an output of 60 degrees, then this means that the average radiator water temperature would be 70 degrees. Delta T = (Room temperature) - (Average radiator water temperature).

Different radiators produce different outputs from different temperatures flowing into them.

Delta u standard calculator