"IMM" wrote in message
...

snip

Headers with a condensing boiler, UFH and rads in a domestic system is
ludicrous. I can them suggesting that if two boilers are used, or a
regular
boiler, but a header which raises the return temp is ludicrous.


Doesn't the design of the header and control of the water temperature inside
it mean that the return temperature is low? I found a Viessman manual on
their domestic Vitodens 200 boiler which says a bit more about this
http://tinyurl.com/6cqtt (page 35).

For my application, it seems like the options a
(a) Rely on the condensing boiler pump and zones valves if the load has
sufficiently low resistance. As soon as any external circulation pumps are
required, however, it appears that zones valves cannot be used and a means
of hydraulically separating the boiler from the rest of the circuit is
required. (Heating system suppliers give conflicting advice on this,
however.)
(b) Use a low loss header and circulation pumps in each heating zone.
(c) Use some other means of separating the boiler flow from the secondary
circulation (such as IMM's method).

All UFH suppliers provide a circuit manifold with a secondary pump on the
load side of a thermostatic mixing valve. That would seem to rule option out
(a). However, I bet that a simple zone valve system is (erroneously) used
with these manifold/pump arrangements in most UFH installations. The UFH
suppliers don't seem to specify headers or heat banks.