This month I'm in the middle of a thermal imaging survey in the village. I potter around to people's houses in the evening and look for energy leaks. Everyone has been really nice and I hope I've been able to help them save a few quid and some CO2.
At the same time I'm looking to replace our old Everest double glazing units. Overall the glazing is sound, they are well spaced units and most of them have not blown. I'm not sure of their exact age but they are probably over 20 years old, as they are aluminium frames. So while the glazing is still sound the frames conduct heat like it's going out of fashion... We probably have some of the worst window (frames) in the village.
I've started the process of getting quotes for higher performance modern triple glazed windows with proper engineered frames that result in an overall "A rated" unit. Suffice as to say the prices are many thousands, the current highest quote for all new British made, top end windows is £25k.
If you believe the glass and glazing Federation, replacing our old windows with modern BFRC "A rated" ones and assuming 4% fuel inflation they calculate over 25 years a saving of £8k and just under 7 tonnes of CO2,
Based on my own figures, running a 12.3 MWh annual gas usage and using the same 4% inflation I calculate a similar saving if you assume that windows account for over 35% of all heat loss in the house. The house was built in 1936, so it's a bit leaky, so I'm not convinced that the windows are as much as 35% of the total loss. The loft is well insulated to about 40 cm of insulation, but the cavity walls were filled several years ago and I'm not convinced it was done that well.
If you assume more gas inflation then the savings come in quicker or require the glazing to be less of a source of heat loss. To get my money back on £25k, I would need to wait 30 years, at gas inflation of 8% and assume that withe windows contributed to 45% of all heat loss.
As much as I would like to buy British made, "A" rated windows, and assuming gas prices rise faster than general inflation, it just doesn't make economic sense to buy top of the range. Imported windows of similar quality cost considerably less and I will break even with them - eventually!