If you are still there Oilman..,
The existing windows are very old, with poor quality glass that has sagged over the years making for a wobbly view. (Some people like this - not me!) The paint job is appalling with great splurges of paint on the glass, and the putty is falling out. So I'm in for a renewal of some kind or other. The timber framing is sound. So my options are:
Do nothing,
Re-do the painting and live with the wobbly glass,
Get in the double glazing cowboys with their chain saws and angle grinders, not to mention the infuriating salesmen,
Obtain dg units from the glaziers and stick them in myself. Hence the query in the forum.
The benefits are: I get a spanking new, nice looking bay window, more warmth ( I will only keep one opening sash, the others will be fixed - so minimum draughts). Whether it takes 5 years or 50 years to re-coup the expense is not really the issue. Do you have any experience of this or are you just passing the time of day? (no insult intended!)