In article ,
"Doctor Evil" writes:
How many bathroom, showers, etc? Combi's are arted on "flowrate" of hot
water, so don't undersize.

Check the minimum pressure it will work at, and the minimum
pressure your water company is intendeding to provide in the
future. Anglian Water circulated a warning with my last bill
saying that if you intend to fit a combi, it must be suitable
for working down to 0.75 bar. I presume they are planning on
following Thames Water and dropping mains pressures to meet
their leak targets.

--
Andrew Gabriel