Just look at it this way and think about the merits of working it out properly rather than pacing the floors out and using some handed down coefficient, someone asks you to put central heating in an old bungalow built in 1950, new had a system in before its been recently rendered and the owner has just died and the new owners are asking you to size up everything, a friend of yours is building a new bungalow and the rooms by some quirk of fate are exactly the same size as the first bungalow, how much small will the radiators be in the new house by % and how much smaller will the boiler be. If you were to just have a simple guess I wonder what people would come up with in % terms, if you had a spreadsheet it would take you 2 minutes to change the "U" values and the ACR.
Kris is nearer the mark, he knows if he makes a mistake in his calculation he is the only one to blame, don't know how you would bollock an app and tell the custard when they are cold " its was my mobile that told me how to do it". Bet they do a pipe sizing app too.
It's the thin end of the wedge guys, perhaps this is why so many people are fitting there own installations and just get a GSR to do the fiddly bits, we need to keep a little bit of professionalism in our trade even though it is all slipping away from you, push fit is also tipping the scales too.
Bald Old Git that really does miss being on the tools and miss the smell of new radiators when you first turn on, water based paints don't smell any-more, where will it all end.
Look whatever way you are happy with and you don't have to go back and put a bigger rad in on a regular basis, if a rad is too big you will never know the TRV will take care of that.
