Try This Quick Test for Air Leaks
Among the quickest routes for heated air to escape from your nice, warm home during the winter are the same ones where cold air finds its way in: through windows and doors. Air leaks are a waste of energy, and they can occur around windows and their frames and even right through the glass.
To find leaks, try this test: On a windy day, light a stick of incense and hold it next to a window. If the smoke travels horizontally, you've found a leak. You can use the same test to find leaks around doors, plumbing fixtures, electrical outlets and other potential escape routes for heated air.
Once you find a leak around a window or a door: