BTU Heat Loss Calculator
BTU Heat-loss Calculator (ΔT50)
Our BTU calculator helps you estimate the amount of heat your room loses per hour as well as how much heat is needed to comfortably warm your room. Results are shown using the UK standard measurement of ΔT50 BTU/h, which reflects the output of radiators when used with a typical gas-powered central heating system.
if you are are in a remote area, in the highlands and islands, we would recommend using conservative mode to allow for colder minimum temperatures.
Why are Heat pump systems different?
If you’re using a heat pump, radiators operate at lower water temperatures, so we also provide an equivalent ΔT30 calculation. This allows you to easily compare outputs and choose a radiator that will perform effectively with your heating system, whatever type you use.
Radiator heat outputs are measured using a temperature difference known as Delta T. Delta T50 is the traditional UK standard and reflects the higher water temperatures produced by gas central heating systems. Heat pumps operate at much lower flow temperatures, which is why their performance is measured at Delta T30. Because radiators emit less heat at these lower temperatures, a radiator sized for Delta T50 will produce significantly less output when connected to a heat pump. To fully replace the heat lost from a room when using a heat pump, radiators must therefore be larger or more efficient, ensuring they can deliver the required heat output at Delta T30 for comfortable, consistent warmth.
Understanding your results
We calculate your heat requirement using your room size, construction details and how the room is used.
Different rooms are typically kept at different temperatures — for example, bathrooms are usually warmer than bedrooms or living areas (22°C vs 18°C).
The way your room is built, along with the style of windows, affects how quickly heat is lost, so these details help us estimate how much warmth is needed to keep the space comfortable.
We also factor in an estimated outside temperature to reflect typical winter conditions (Default: -3°C).
Together, these assumptions help us recommend a radiator size that will comfortably heat your room, even on colder days.
BTU Calculator Disclaimer
This BTU calculator provides an estimated heat requirement based on a typical UK home at Delta ΔT50. Actual performance may vary depending on factors such as installation quality, building construction, insulation, air changes, and the overall efficiency of your heating system.
For best results, we recommend rounding your calculated BTU requirement up to ensure a comfortable heat output. If you have a complex layout, an unusual property type, or require a precise calculation, please consult a qualified heating engineer.
All radiator outputs listed on our website use Delta ΔT50 for standard UK central heating systems and Delta ΔT30 for typical domestic air-source heat pumps. If you require a different Delta T rating, please use an appropriate conversion tool.