This is a thermal imaging study conducted a few years ago – before we built the extension on the back of our house.
If you ignore the red door-frame on the left (it’s an internal door so doesn’t count) and the bottles on the windowsill, then you can see the window and the outside wall.
The window was double glazed and the wall surrounding it is a solid (double) brick wall, which was rendered on the outside but not plastered on the inside. The wall is actually losing more heat than the window!!! (Areas of worst heat loss in this context is dark blue.)
This part of the house was demolished to make way for the new, well-insulated timber framed extension, so the energy losses should be much, much lower now.
Because we did like the look of the original bare bricks we wanted to incorporate that look into the house in a way that wouldn’t be so disastrous in terms of energy loss. To do this we had the render removed from the kitchen wall – previously an external wall – once that had become part of the middle of the house, when the extension was built around it to expose the bare brickwork there.