Windows do lose more heat than walls.
Windows and especially single pane windows are poor insulators when compared to walls which are properly insulated.
A significant portion of heat in the home or building is lost through the windows.
With a properly insulated home you'll lose more heat through windows instead of your walls.
However if your walls are not properly insulated or not insulated at all then you can also lose lots of heat through the walls as well.
In older homes they sometimes don't have any insulation in the walls, especially if the house was built 100 years ago.
You can drill holes on the exterior of the walls between the studs and force insulation through the hole into the walls with a machine.
Double pane windows or other insulated windows lose less heat than single pane windows.
Upgrading your windows can help to keep your home warmer in winter and cooler in summer and help lower your energy bills as well.
Single pane or single glazed windows lose around 10 to 20 times as much heat as the same area of a wall that is properly insulated.
Storm windows or double glazed sealed windows will reduce the heat loss by almost half.