On 05/12/2011 15:14, Lieutenant Scott wrote:

But getting hot isn't enough with condensing boilers, the rads have to
drop
the return temp to about 50C so the boilers condense while still
providing
enough heat to do their job.
This can be somewhat difficult if a lot more water is going through
one rad
than another.

Then don't use a condensing boiler.

These days you don't get much choice. Except for certain very limited
exceptions condensing boilers are mandatory both as new installations
and as replacements.

I have what he called a balanced flu.

So do most people these days. You could well have a condensing boiler
without knowing it.

I think you need to read up on the basics of central heating design
which should include inter alia boiler types, heat output, circuit
design, pipe sizing, etc.

Then there is the more sophisticated stuff - programmable thermostats,
zoning, weather compensation, heat recovery ...

--
Roger Chapman