I have a bedroom 8ft x 9ft x 8.25 ft high, in which I am replacing the radiator. There are two external walls (one north facing) each containing a window (single glazed). I estimate I need a radiator with an output of around 2,800 BTU/hr. However, there appears to be two ways of calculating the output of a rad - one using a delta 50T calculation the other with delta 60T - which gives two figures for each rad. How do I go about working out which one to use for my particular heating system?
Radiator output
- Thread starter JackieDee
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whats above and below room and what is the wall thickness(solid or cavity) whats the glass size
THe equation to work out a rad size is: Height of room X Width of room X Lenght of room Divided by 20. This will give you what you need in Kw. If you want to convert Kw to Btu 1kw= 3412 btu.
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Prof.plumb said:
This will give you a rough calculation. You really need to take into account the walls, floors, windows, insulation etc etc. This is quite a good calculator http://www.kermi.co.uk/Kermi/kermi....ns/Heat-loss?sid=4xe68QOb17ylewzC9PClQg&iid=2
It is in Meters. Yes it is rough but quick and very close. If it has external walls no cavitys etc just add a bit on.
That`s not a bad estimate, my Mears (imperial) says between 2600+3300 depending on wall type. Rad output tables are calculated on doo dah 50. I spent hours trying to work it all out with a mate who teaches maths.and it all came back to the trusty Mears circular placcy calculator 
Just go larger + stick a TRV on
Just go larger + stick a TRV on And now to answer the actual question ....
The two figures are related to the radiator specs and type of boiler. In the past, Delta-T 60 was conventionally used on the assumption that the room temperature was 20 and the radiator at 80 degrees - difference 60. But if you run a condensing boiler at 80 degrees it will never (well - hardly ever) condense. So rad manufacturers are starting to specify their rads using Delta-T 50 (room temp still 20 but boiler output at 70). Only problem is that with most systems if the boiler stat is set to 70 degrees, Return water will still be at more than 56, the critical temperature for condensing to happen.
The two figures are related to the radiator specs and type of boiler. In the past, Delta-T 60 was conventionally used on the assumption that the room temperature was 20 and the radiator at 80 degrees - difference 60. But if you run a condensing boiler at 80 degrees it will never (well - hardly ever) condense. So rad manufacturers are starting to specify their rads using Delta-T 50 (room temp still 20 but boiler output at 70). Only problem is that with most systems if the boiler stat is set to 70 degrees, Return water will still be at more than 56, the critical temperature for condensing to happen.
Hahahah you want to tell me when someone asks for a rad in a room you analyse the boiler get your fancy calculator out scratch you head for an hour and look a novice or do you get it done quick, fairly accurately and get gone. Nige is right do my equation go bigger and put a stat on. Beautiful!
Nige F & Prof Plumb (!) If you want to be rude - suit yourself.
The original question asked about Delta-T values. I explained.
You have a problem with that?
Undersized rads resulting from installers using inaccurate Rules of Thumb are a main reason why at least half the installed condensing boilers only condense a small fraction of the time.
Oh- sorry! You mean you DON'T actually check the return temp when you do a boiler change. I must have over-estimated your competence.
The original question asked about Delta-T values. I explained.
You have a problem with that?
Undersized rads resulting from installers using inaccurate Rules of Thumb are a main reason why at least half the installed condensing boilers only condense a small fraction of the time.
Oh- sorry! You mean you DON'T actually check the return temp when you do a boiler change. I must have over-estimated your competence.
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