My parents’ gas bill went up tenfold for some reason, and while the two boilers almost certainly acted up (we think they kept starting and stopping), they live in a Tudor Revival with nasty single-pane windows and now we have an excuse to rip them out. Given the temperature difference in Centigrade and total area of the windows in square meters, can I do any back-of-the-envelope calculations?
The heat transmission of a 3mm-thick glass pane is about 300 W/sqm.°C. This goes down to about 3 W/sqm.°C for basic double-glazed glass (and even further if at least one pane has anti-radiative coating).
Thus, single pane glass has a heat resistivity of about 0.003 sqm.°C/W and double-glazed about 0.333 sqm.°C/W. Together with an estimate of the ambient air resistivity of 0.15 sqm.°C/W, this is a total system resistivity of 0.153 sqm.°C/W with single pane and 0.483 sqm.°C/W with double-glazed.
Finally, taking reciprocals again, this is a system transmission of about 6.6 W/sqm.°C for single pane glass and about 2.1 W/sqm.°C for double glazed.
At 10 sqm of windows and a 15°C temperature difference on average, over 24 hours, this is an energy bill of about 16.8 kWh per day for single pane glass – and only a third, down to 5.6 kWh per day, with double glazed.