Do you know where most of the energy loss in a building happens? Using thermal imaging will help in finding spots, but there is definitely a weak spot whenever you have windows. Even with double-pane windows, you’re going to lose some energy, but if there are cracks and holes in the window frame, that is not going to help things. Knowing the problem is half the battle, but it will require some work to stop the energy loss and still keeping the windows looking good. If you have wooden frames around the windows, some wood repair can make things a lot better.
If the leak is due to wood rot, then you should start by cleaning out the rot as well as possible, even digging into the good wood a little bit. This is to ensure that the rot won’t take hold again. Leaving just a little bit behind will allow the problem to start growing again quickly.
To make everything look good again, you can use wood-filler which then can be painted for a nice finish.
