"Tom" wrote in message
...

Most manufacturers seem to recommend setting flow rates in CH systems to
achieve a rise of 11deg across boiler, why is this? is it the most
efficient
setting for heat transfer?
Tom

The prime aim in regular boilers is to avoid condensation in the burner box.
Regular boilers should always be set as high as possible, and "never" below
65C flow temp. Some regular boilers only had a high limit stat and the flow
temp pre-set.