Assumptions - BTU Estimators

[Diggory]

I’ve been using on-line BTU estimators for some radiator sizing.
I (perhaps wrongly) assumed that the input of room dimensions (LxWxH) was simply to calculate a volumetric area.
After getting some inconsistent results - I reversed my L and W dimensions; keeping the same numbers / same room volume.
And I got very different results - do estimating tools make an assumption that the length (L) of the room will be the outside wall ?

Thanks D

 

[flameport]

Anything still using BTUs is decades out of date and should be ignored.
Same for anything that makes assumptions about what walls might be external or not.
Some rooms don't have any external walls.

 

[Diggory]

Thank you for reply.
Grateful if you could suggest / recommend something that I should use.

Best D

 

[Diggory]

and should be ignored.

Following the above comment
Anyone got a recommendation
D

 

[Diggory]

I’ve tried to find something better and have had a go with ADVANCED STELRAD STARS.
Unfortunately, the User Guide link doesn’t seem to go anywhere - anyone know where to locate this ?
There is also a BASIC STARS - is this any good ?

Also - looking at this one - seems to give similar results to ADVANCED STARS.
Can anyone recommended this one ?

Thanks D