Why does adding a second pane of glass (double glazing) make such a huge difference, even if your walls etc are the same?
In: Physics
Walls are thicc, windows are not
Your wall has drywall, wooden studs with insulation, an outer wooden layer, a heat and vapor barrier, and then the final siding. None of these things are good conductors, and the fiberglass insulation in the middle prevents convection from helping so it is very hard for heat to move through the wall
The single pane window is think and can conduct straight from the warm air in the house to the cold air outside(or vice versa), adding a second pane removes the conduction path as the heat has to go through the first one, hop into the air, go from the air to the second pane, and then conduct through that. Thickness and transitions both help slow down the heat transfer.
A basic single pane window will come in around R-1 (R factor measures heat loss in ft^2 * F * h/BTU, basically higher means less heat lost), a double pane window can be around R-4 meaning it loses heat at a quarter of the rate over the same area, while a wall can be upwards of R-20 so it loses 1/5th the heat of the fancy window over the same area. You do have more wall area but windows lose a crazy amount of heat for their relatively small size. A 2’x3′ R-1 window loses as much heat as a 10’x12′ chunk of wall while a big 5’x5′ picture window could lose as much heat as 10’x50′ of wall, that’s the entire length of most houses!
Windows are the easiest improvement that can be made without radical design changes, and considering how quickly they lose heat through their relatively small area they can have a considerable effect. Houses in northern regions are built with highly insulating walls and require the higher end windows, and have ceiling insulation requirements of upwards of R-40 to keep all the heat inside in the winter.
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