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[KeithD]

If you are worried about carbon footprint, plant a couple of shrubs, that will more than compensate.

Boy am I glad you're not doing the global warming maths

Look at the cost of double glazing, split it over the expected lifespan, and you will never spend that much in heating for the +-7% advantage gained

You've missed the main point...double glazing increases the value of the house when sold, so any savings on heating are savings.