On Fri, 06 Jan 2006 01:06:52 +0000, DJC wrote:

John Stumbles wrote:
On Thu, 05 Jan 2006 14:24:55 +0000, DJC wrote:
John Stumbles wrote:
My spreadsheet is at http://82.24.138.95/~john/boiler_sizing.xls (or
http://82.24.138.95/~john/boiler_sizing.sxc if you have OpenOffice)

Seems to be broken on your spreadsheet too. (OO version).

Perhaps it is just rather confusing then; a case of the user interface
rather than the calculation itself. A note that putting 0 in the roof
section is an option rather than "Put '1' in one of these boxes"

User interface?!!! :-)

It was never meant to be particularly user-friendly, just something I
knocked up for myself to do the calcs to my own satisfaction. I thought
I'd better put in some explanatory notes if I was going to put it up for
others to use, but thanks anyway on how I could explain it better. However
it does really presuppose an understanding of the method, which I think
is described on one of the sites I mentioned in my post in reply to Ed's
about the boiler FAQ.

Perhaps as the the roof calc is conditional on B9 being 1, a note to
the effect that "Nr. of external walls,roof,floor" can be modified from
the default. I realise a roof and a ceiling are not the same thing but
these things do confuse, even if the roof is not imediately below my
flat I still have a roof over my head.(Is there always a floor value for
a flat or does floor in this case mean ground floor?)

Ground floor: this is a simplified calculation which ignores heat losses
through party walls etc assuming that adjacent buildings will be equal
temperature. I was skeptical at first about many of the simplifying
assumptions but it seems that whoever devised this method have checked it
out reasonably well and made sure that the simplifications involve
small enough errors that the overall results are still valid.

Also I need to set the window factor to 0.35 rather than 1 to make
window area represent my window area

I'm not clear what you mean about the window factor - the value for a flat
is 0.25, which is what you should set.

... And External walls 1.5 allowing
for the stairwell in common parts.

I'd treat the stairwell as external unless it's well heated.

The point about this method is it is simplified so don't try and fine-tune
it for your particular place: if you want a more accurate calculation you
can do a full heat-loss calc for each room as per the Myson or Barlo
calculators (I also have a spreadsheet I use to do this but I wouldn't
dream of exposing it to public scrutiny!)


Water heating default is 2000kW, not 2kW?

Oops, yes.


Depending on how I interpret the required input my results vary from
4.6kW to over 7kW.

[No matter in my case, as that's less than the lowest modulated output
of my combi.]