On Sat, 11 Sep 2004 23:57:46 +0000 (UTC), (Fred)
wrote:

I am about to install a new combi system in a four-bed house - don't
lecture me on tanks please - but I am unsure about combi capacity. Is
bigger flow always better, equalling buying the most expensive boiler
I can afford basically? For this little excercise, capital cost for
the boiler shall not be important, I am interested in the priniciple
rather the practical.

Fred

In this case, bigger is better.

Combi boilers are specified in terms of the rate of flow that they can
achieve for a given temperature rise - usually 35 degrees, but do
check specs.

In the winter time, this figure will equate to the maximum flow for a
shower or for filling a bath. Considering that a bath needs 100
litrres for little more than a splash in the bottom or 150litres plus
for a reasonable one, then a typical 13lpm combi will take 10 - 15
minutes to fill it at 40 degrees. You need to decide whether you
are OK with this.

There are domestic combis with flow rates of 22lpm, which is obviously
a lot better, but these are not at the cheap end of the scale.

For almost all with any significant power level, an upgrade to 22mm or
above of the gas pipe from the meter to the appliance is needed if it
hasn't been done already.


..andy

To email, substitute .nospam with .gl