Sizing rad's with boiler upgrade in mind - delta_T50/_T60 ??

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I’m currently sizing some additional radiators for an existing central heating system (all rad’s have TRV’s) that has a non condensing combi boiler that’s around 8 years old. The new radiators will be fitted in the next few weeks but I’m planning on changing my boiler in a year or so.

Am I correct in assuming that radiators that are served by new condensing boilers should be calculated using delta_ T50, and delta_T60 should be used for non condensing boiler systems? If so then I believe I have to buy radiators that have too large a capacity for my current boiler in anticipation of fitting a condensing boiler that runs at a lower output temperature.
For example - for a calculated room requirement of 4110 Btu, a radiator of Btu/h 4587 at delta_T60 should suffice for my current boiler. When I then change to a condensing boiler, I believe that this radiators capacity reduces to an output of Btu/h 3620, thereby not providing sufficient heat for the room.

I’d appreciate if someone could confirm (or otherwise) the above assumptions before I buy inappropriate radiators.

Thanks in advance.
Antony
 
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Most rad makers data now is stated at T50 and thats what you should use.

Older rads were sized by the installer for T60 but since then the insulation has usually been improved. Also most heat loss programs used to oversize the rads anyway.

Many people are still using heat loss programs based on T60 and thats where many people can get into difficulties.

Its all very hit and miss anyway!

You only need the full output when the temperature is at - 1 ° C anyway. Thats hardly a couple of days a year in low lying southern areas.

Tony
 
Places like Yorkshire don't matter to Tony :D :LOL: :eek: :p :cry:

And the standard is now -2ºC
 
Am I correct in assuming that radiators that are served by new condensing boilers should be calculated using delta_ T50, and delta_T60 should be used for non condensing boiler systems?
deltaT is the difference between the mean radiator temperature and the design room temperature. The reason for adopting a deltaT of 50°C instead of 60°C was to bring England into line with the rest of Europe. It also saves energy as you only need to raise the water temperature to 75°C instead of 85°C. The conversion factor given in radiator calculators for different deltaT assume that the flow temperature is 75°C and the return is 65°C. The change in deltaT is due to a higher/lower room temperature.

Some "experts" suggest that, for maximum efficiency, the boiler should always working in condensing mode. To achieve this, the return temperature has to be below 60°C. The flow temperature required to provide this return temperature will depend on the boiler. Unfortunately the flow and return temperatures will not be as assumed in the rad literature, so the conversion factors will be different as well.
 
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I always use deltaT50 and run the boiler at 60C (combi) 65C conventional boiler.

Never had any probs reported back to me yet ;)
 
Thanks for your replies & comments everyone.

I reckon common sense suggests using deltaT50, ensuring that I'm 'future proofed' when I eventually go for the condensing boiler.

Cheers
Antony
 
Places like Yorkshire don't matter to Tony :D :LOL: :eek: :p :cry:

And the standard is now -2ºC

"""The British standard BS 5449 states that the external design temperature should allow for all but the most extreme conditions and a figure of -1 degrees C is usually chosen. Many developers still rely on this minimum BS Standard of -1 degrees C irrespective of the anticipated external temperature extremes."""

Has BS 5449 been revised then?

Tony
 

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