On May 9, 10:24*am, John Rumm wrote:

Its a payback trade off question really. If you assume the average
temperature differential across the window is 10 degrees. You have not
specified the total window area, but for the sake of argument, lets say
it amounts to 20m^2 for all of them. The difference between u values of
2.1 and 1.4 would translate into difference in rate of heat loss of 2.1
x 20 x 10 - 1.4 x 20 x 10 = 140W, or energy loss of 3.36kw/h per day. So
at 8.45p per kw/h that amounts to 28p/day. If you are paying that for
120 days a year, then about £33/year. That would mean a 20 year payback
(ignoring loss of interest on the money or cost of borrowing - whichever
is appropriate) on the extra cost moving from air to krypton (assuming
the units stay sealed for that long). Although you can factor in a
better comfort level with the better u Values.

etc. Wow - I'm incredibly impressed at this answer. Wish I could rate
it!
That's really given me something to chew on, some questions to ask of
the company... oh, and thanks for the DIY FAQ link too (now
bookmarked).

(It's good to see people still using calculations in working things
out - I was watching a thread on a forum about solar PV and feed in
tariffs, and it seems that actually thinking and calculating when it
comes to micro-generation is actively discouraged.)

On May 9, 10:19 am, Tabby wrote:

Gas fills are used to improve the u values when new, what they don't
mention is the gas then leaks out, and performance deteriorates. You'd
get the same gain when new by adding a secondary glazing pane to your
existing dg, the 2 differences are that the insulation gain would be
permanent rather than temporary, and it would cost less. If you added
a clear plastic film on the window side of this new glass pane, spaced
off it, you'd have quadruple glazing, with even better gain.


Hi Tabby,

a good thought, but due to the shape of the existing windows,
secondary glazing has been ruled out as awkward.
Plus the fact that a fair few of the original units are leaky and
clouded up means it's probably time to make the change.
But the plastic film idea sounds interesting, must look into (or
through!) that.