On 2006-10-16 15:37:12 +0100, said:


Guy King wrote:
The message
from The Natural Philosopher contains these words:

Also bolers are more effcient at lower temps I THINK. Not sure ..

They should be. You can't transfer energy so easily into a warm body
from a hot one as you can into a cool body from a hot one.



ta da - so isn't it the temperature difference between hot feed and
cold(er) return that is of importance?

There are two things

- The temperature drop across the radiator (flow and return).

- The temperture difference between the radiator and the room air temperature.

If you look at radiator manufacturer data sheets, you will see that
they publish tables of numbers to allow you to work out what the actual
heat output will be as opposed to the specified figures used in lab
tests. The latter are done according to a standard which uses 90
degree flow.
the tables work on the basis of Mean Water to Air temperature (MWTA)
which is calculated by taking the mean water temperature (Flow +
Return)/2 and subtracting room temperature from that.

You will end up with a factor that is multiplied by the nominal output
to give the actual output under those operating conditions.