On 26/04/2012 21:28, Stephen H wrote:
On 26/04/2012 21:12, kent wrote:
On Thursday, 26 April 2012 20:25:40 UTC+1, YAPH wrote:
On Wed, 25 Apr 2012 12:51:19 -0700, kent wrote:
Oh dear, I didn't mean to stir the s*** ! Does this mean I am unlikely
to get any rational answers?!
No, it just means you are likely to get some irrational ones ;-)
Multiple boilers in larger properties is quite a sane idea. Generally,
however, they are ganged together so that either boiler can run quite
efficiently at the lower output required for heating in spring and
autumn-
ish weather, with both coming on together for winter loads. This also
gives a degree of fault tolerance as a fault in one boiler doesn't leave
you entirely without heating, and may not even be noticed in milder
weather. However the controls required (including a mechanism for
detecting that just one boiler has failed, before the other one goes as
well and you really don't have any heating!) is more complicated and/or
expensive.
Combi boilers aren't generally ganged though: in the larger
properties in
which ganged boilers would be called for the hot water demand (e.g.
multiple bathrooms etc) is likely to be greater than even 2 combis
working together can supply.
However a 4 bedroom house isn't large enough to likely require more
power
for heating than a single domestic boiler can supply (and if it does
you'd be better advised reducing the heat losses than adding boilers!)
Given that the hot water requirement is the critical factor then some
form of stored water system ('Megaflo'-type unvented, or thermal store/
heat bank) or just a storage combi (e.g. Worcester's Highflows) would be
more appropriate. If you are seriously concerned about backup for when
the boiler goes down a stored water system with immersion heater and a
few cheap convector heaters stored in the attic should do the trick.
--
John Stumbles -- http://yaph.co.uk
The astronomer married a star
Well John it certainly has made for some interesting reading and
encouraged me to look a few technical points up on the internet. The
conclusion I have come to is that for our four bedroom house I just
need a condenser boiler to replace our old regular one (making sure
that the condensing pipe is not in a location where it might freeze
up) and install an electric shower if we really do want three people
showering at the same time! Any idea how much just replacing the
boiler might cost (with labour, not diy)?
The idea of having combi's really came from my wife who wants the
airing cupboard space!
Anyway, thanks to all for your comments and suggestions.
Having two combi boilers also allows you to have two zone heating as well.
You can have two zones with a single boiler, or two even if put in parallel.
This could help you to use gas more efficiently if you use a pair of
programmable room thermostats. These PRTs allow you to have different
temps during the course of the day, so during the night , you'd heat
upstairs only, keep downstairs at 5°C. During the day, you'd heta
downstairs only, and keep upstairs at a lower temp.
You'd have a downstairs boiler doing the downstairs rads and the
downstairs hot water taps.
You'd have an upstairs boiler doing the upstairs rads and the upstairs
hot water taps.
One of teh boilers could go where your existing boiler is, the other 2nd
boiler could go where your hot water cylinder is.
YOu may need to revise your heating pipework to get the two heating
zones created though.
Its a trivial matter to put in some 2 port zone valves on both the hot
water and the heating loops and a special switching arrangement so that
if one boiler fails, the other working boiler can then take on the whole
house..
Then why not have both boiler in parallel in the first place??
In the past I have had two boiler, each having a non-return valve and
its own pump, such that you have the choice of one running, or both
depending on the need for heat.