BTU online calculators

[ShelCOYS]

Hi, I need new rads for a whole flat and been doing the BTU calculations. Only thing I am finding is that the online calculators are coming up with completely different results, e.g. Living Room for First Floor, 6m x 6m double glazed room, 2.5m ceiling - one set of online calculators say about 5,000 BTU and the anothers are s15,000 BTU - obviously massively different?? Appreciate any advice.

 

[Last Plumber]

Do these 'online calculators' ask for:-

length, breadth and height of the room.
How many outside walls
What floor (solid or suspended)
What the target temperature is.
Type of wall and whether it is insulated.

Does it say what outdoor temperature the calculations are using.

There is more information than that required for these calculations but I would expect them to require at least those questions above answering.

I have looked at one or two online calculators over the last few years and found them to be useless. That is of course my opinion on it and it could be that I haven't found one whose results I agree with.

 

[exedon2]

I've used stelrad stars (version you have to register for ) for few years now.
All parameters are adjustable out side temperature air change
Add a percentage for quick heat build up ect.
Only down side is you probably have to have a fair understanding of heat loss calculations to get best from it.
Better than when I first did them long hand table of heat loss with the aid of a slide rule!

 

[AWheating]

City plumbing heat loss calculator is a good one.