{"id":4691,"date":"2026-02-13T09:12:47","date_gmt":"2026-02-13T09:12:47","guid":{"rendered":"https:\/\/www.showerstoyou.co.uk\/latest\/?p=4691"},"modified":"2026-02-13T09:12:47","modified_gmt":"2026-02-13T09:12:47","slug":"what-is-delta-t","status":"publish","type":"post","link":"https:\/\/www.showerstoyou.co.uk\/latest\/2026\/02\/what-is-delta-t\/","title":{"rendered":"What is Delta T?"},"content":{"rendered":"

Buying a new radiator or <\/span>heated towel rail<\/span><\/a> involves more than simply choosing a design that looks good in your bathroom. To ensure your room stays warm during the British winter, you need to understand the technical specifications behind the heat output. One term you will frequently encounter is “Delta T” (<\/span>often written as \u0394T<\/span><\/em>). But what is Delta T?<\/span><\/p>\n

Understanding this figure is vital. If you ignore it, you risk buying a radiator that leaves your bathroom cold, even if the product description promises high heat output. This guide from <\/span>Showers to You<\/span><\/a> explains exactly<\/span> what Delta T is, how it impacts your central heating choices, and how to ensure you select the correct product for your home.\"What<\/span><\/p>\n

Understanding Delta T<\/strong><\/h2>\n

In simple terms, what is Delta T? It is the difference between the average temperature of the water inside your <\/span>radiator<\/span><\/a> and the temperature of the room you want to heat.<\/span><\/p>\n

Heating engineers use this figure to calculate a radiator’s actual heat output in a specific environment. The heat output quoted by manufacturers – usually in British Thermal Units (BTUs) or Watts – is based on a particular Delta T assumption. If your central heating system runs at a lower temperature than the manufacturer assumed, the radiator will produce less heat than advertised.<\/span><\/p>\n

For more information on BTU, check out our <\/span>guide on British Thermal Units.<\/span><\/a><\/em><\/p>\n

The Calculation<\/strong><\/h3>\n

To work out the Delta T of your system, you need three figures:<\/span><\/p>\n

    \n
  1. Flow Temperature:<\/span><\/strong> The temperature of the water entering the radiator from the boiler.<\/span><\/li>\n
  2. Return Temperature:<\/span><\/strong> The temperature of the water leaving the radiator.<\/span><\/li>\n
  3. Room Temperature:<\/span><\/strong> The standard desired room temperature (usually 20\u00b0C).<\/span><\/li>\n<\/ol>\n

    The formula works like this:<\/span><\/p>\n

    (Flow Temp + Return Temp) \u00f7 2 = Mean Water Temperature<\/span><\/em><\/p>\n

    Mean Water Temperature – Room Temperature = Delta T<\/span><\/em><\/p>\n

    For example, if your mean water temperature is 70\u00b0C and your room is 20\u00b0C, your Delta T is 50 (70 – 20 = 50).<\/span><\/p>\n

    The BS EN 442 Standard<\/strong><\/h2>\n

    To make it easier for customers to compare products, the industry adheres to European Standard BS EN 442. This legislation ensures that all radiators and towel rails are tested under the same conditions. When you see a CE mark on a radiator, it verifies that the heat output data has been independently verified.<\/span><\/p>\n

    According to BS EN 442, the standard test condition is <\/span>Delta T 50 (\u0394T50)<\/span><\/strong>.<\/span><\/p>\n

    This standard assumes:<\/span><\/p>\n