Jim Alexander wrote:

"Ian Stirling" wrote in message
...
Doctor Drivel wrote:

With a condensing boiler, balancing the rads and boiler to have a wide
flow/return temperature differential means smaller bore pipes can be
used.
If 8mm was fine before it will be more than fine now.

There is a small, but significant energy gain on a condenser, by keeping
the temperature difference small.

That doesn't make sense. What temperature difference exactly? Not "wide
flow/return temperature differential" as correctly stated by DD. Perhaps
you mean keeping a low average flow temperature, in which case 8mm will
suffice perfectly but the radiator output will disappoint.

For a given balanced system, with a given pump, there will be a certain
flow.

The higher the flow, the lower the temperature difference between flow
and return.

Increasing the flow will therefore decrease the temperature of the flow
pipe, marginally, or perhaps not marginally increasing the efficiency of
the condenser, by allowing it to condense more water from the gas
exhaust.