The most accurate BTU Calculator

[DarkDarkNight]

I am going round in circles looking for new column radiators as every BTU calculator is giving me completely different results even using the same measurements. My plumber is very reluctant to do it and a local supply shop said plumbers don’t like to in case it’s wrong and they get the blame 😫

Is there a standard one, or one considered more accurate? For one bedroom I have had results ranging from 1609 to 3950 and everything in between.

Use the one for a radiator manufacturer I think. You can vary the warm up factor on the myson one, that makes a big difference to the sizing. Use a site where you can enter all the factors eg target temp, outdoor temp, flow temp, Delta t, and then you can take everything into account.
The most accurate would be wait until winter and put a thermostat controlled electric heater with an energy meter plug socket in line, but I don't think that's a good idea!

Thank you, I will give it a go. I’ve only used retailer ones so far. No, I don’t fancy waiting until winter!