On 25/04/2012 23:58, John Rumm wrote:

As to multiple showers, much depends on the shower in question and its
consumption. At a previous place I installed a 35kW combi when
converting the loft and losing the space for the cylinder etc. That
could (just) manage two showers at a time if there were no other demands
for water in the house while they were going on (there was a detectable
loss of "power" to each though).

I ran mains water feed in 22mm right through to a 35Kw combi. and 22mm
out where it splits to 15mm to go upstairs and downstairs bathrooms.

After fitting a Mira Eco shower head to one shower (introduces air into
water flow) the boiler quite happily runs both showers at once with no
noticeable fluctuation in flow temp when turning one shower on or off.
Would improve things even more if I fitted a 2nd "eco" shower head the
same, but at the moment the main bathroom has no walls, ceiling or floor
let alone a shower.

And for the record the Mira eco shower head gets absolutely no
complaints from the rest of the fam. but I had to fit the supplied
pressure reducer thingie into the shower hose to stop the vibrations/noise.