External images of windows do not show absolute loss relative to the walls due to the different thermal and reflective properties of glass; however comparison between windows can be instructive.
Images recorded from inside on cold evenings always show up even the best double glazed windows as blue – or at least with blue tinges where the draft leaks in and cools the frame. The standard to match now is moving not to double glazing, but to triple glazing. However this is still expensive, as is replacing any window, especially if it’s an intricate sash design.
Modern double glazing (upper windows and front door) performs better than older double glazing (bottom right)
What the camera does reveal is how much can be done with window coverings. The best example seen was a house where the windows were covered both with blinds and then curtains on top: very little heat escaped leaving the rooms nice and cosy. In addition, investing in curtains with thick thermal linings can cut heat loss through windows. Make sure they don’t hang over a radiator preventing the heat from getting into the room, and remember to draw them at dusk.
An image from inside the house which shows how cold windows are, and the importance of keeping curtains closed.
Secondary glazing is helpful and comes in many different forms, the cheapest being shrink wrap (like cling film) held in place with tape and smoothed by being gently warmed with a hair dryer. Some handymen can make secondary glazing on a wooden frame with shrink wrap. Magnetic panels are also relatively cheap and easy to fix to most windows.