"IMM" wrote in message
...

snip

With condensing boilers headers reduce efficiency. With a condenser you
don't want very hot water feeding right back into the return. This raises
the return temp which reduces efficiency. You want the return temp as low
as
possible.

snip

Won't a modulating boiler adjust its flow temperature and velocity to reduce
the return temperature though? I thought that that was the purpose of the
modulating control.