First of all, will the electrical box be able to support the new fan? A paddle fan takes a special box rated for the extra weight. You can get one for an "old work" set-up and use the same ceiling cut ... read more
Verify that all window and door seals/weatherstriping is in good shape.
Check to be sure doors and windows are caulked properly (no gaps, cracks or missing).
If you have an attic access, treat it like ... read more