In message , Andy Hall
writes
If you mean that SEDBUK says 22kW for a house of a given type, that's
pretty meaningless. It's about as useful as the leaflets in B&Q
which tell you to measure the room, add a fiddle factor and multiply
by aunty's telephone number.

I did wonder..........

There are a number of web sites around that purport to do the sums -
these seem highly variable.

The only two methods I would trust are

- Radiator manufacturer calculator programs (e.g. Myson, Barlo - I
have the Myson one if you want it) but check the U values they use
with those in the Building Regulations Approved Documents and other
sources.

I think I do have one of these somewhere; pretty tedious as I recall.
Perhaps I will impose on you if I can't find my copy ?

- Calculator or spreadsheey and do the sums by hand.
I could do them as well
Again it gets pretty tedious



I plan to have a y plan type diverter and I'd put up with the odd
occasion that I'd need the cylinder re heated from scratch for 28
minutes.


28 mins reheat is not super-fast and you could get better than that if
you wanted it.

Hmmm.I shall look into that...

Remember that if the boiler is reheating the cylinder then the house
will begin to cool - more rapidly if not well insulated. If you have
any rooms where there is a particularly large heat loss because of
exterior walls and large window areas then you will notice more
quickly.





Does this mean I could go for a smaller boiler?
I could use a 622e as this pumps out 22.4 kw or is this too small a
margin?

It doesn't matter for the cylinder. It would be OK for the house if
it really is 14kW.

Both boilers will modulate, although curiously, the 635E goes from
10.5 to 35kW, whereas the 622E is from 13.4 to 22.4kW at 80/60
operation.


More sums then
--
Mark Roberts