cjra wrote:

We have an 1890s Victorian, fabulous HUGE windows, which work great for
natural cooling, but we're installing central a/c and heat. Some panes
are broken and have to be replaced anyway, but what can we replace them
with, without replacing the entire window (for $860/window!)?

What would be the most energy efficient, given the size - can't do
double pane because there's not enough space. We can re-work the
windows ourselves a bit to add an extra 1-2/16s of space to fit glass,
but would such glass be any more energy efficient than what's there?

We have 14 windows - most 8ft x 3 ft (one is 8 ft x 6ft, and 2 are
smaller). Eventually we'd like to make all more energy efficient, but
for now, will just replace the broken ones.

Thoughts?

As Paul notes, replacing w/ thicker single-pane glass will make no
discernible difference in thermal efficiency as glass is a pretty good
heat conductor.

If these are the original windows and they're in good shape yet, I'd try
real hard to preserve them for the originality of the house. If you're
in a large metro area, it might even be possible to find a source for a
glass that will more nearly approximate the original than modern glass.
Depending on your intent on keeping the original character, of course.

It might be possible to have a non obtrusive set of storm windows
designed that would help w/ the heat loss depending on the style of the
windows themselves.

Other than that, I'd try to hold on until I could get a period-authentic
looking replacement if I could possibly manage it.

(Struggling w/ similar problem w/ old farmhouse w/ 6' x 6' 1-over-1
double-hungs w/ leaded glazing in upper throughout the sitting
room/parlor and 3x6 everywhere else downstairs...Temporarily I built
storm windows for the big ones as they are no longer opened...what to do
w/ smaller is still a quandary.)