"Hzatph" wrote in message
...

Where did the 240,000 BTU boiler come from? What size is your house? or
has
an extra nought crept in here?

To answer some confusion, the room stat etc would be on the boiler heating
system - not the Aga.

At present we have two 110,000 boilers on two separate heating circuits
and I want to rationalise with a single circuit and efficient modern
boilers - we have a rambling Victorian place with 28 radiators. Both
installers I have spoken to think we will need a boiler of up to 240,000
BTU capacity.


Ah so IMHO perhaps what you should think about is a large hot water cylinder
with two indirect coils. One fed from the Aga output and one fed from the
heating system. During especially hot weather an immersion heater might be a
useful extra also. In this way the Aga could heat the water in the cylinder
with its slow but useable heat, The main heating system could under
time/temperature control supply any additional requirement and you have the
option of an immersion if and when needed. If the cylinder is sized
appropriately your Aga should be able to look after all your needs except
under occasional heavy demand periods.
I'm surprised by the loading you suggest for the house even if it is
rambling. Have you done any calcs or tried a heatloss program yourself? I
have done a fair amount of work on a house which did have a 210,000 BTU
boiler installed by others but it was never running for any appreciable
length of time before its stat was satisfied. The house pipework was left
over from a coke boiler and under the ground floor was in 4" Cast iron pipe,
reducing to 3" & 2" branches around the (three) floors and serving big old
cast iron school type rads. The house was bloody huge and could have been a
stately home if out in the country rather than in a town. Draining down was
an all day job as was filling up again so the boiler may have been
deliberately (grossly) oversized simply to speed up the time taken to raise
the water temp from cold to working.
I think the old pile would have benefitted vastly from repiping to seperate
the floors into independent controlled zones with smaller pipe and new rads
to reduce volume and speed up the response times but client (as usual in
these cases) wasn't interested in changing