How To Inspect Your Windows For Leaks
1)Start with a visual inspection from the interior and exterior of your home. On the outside you should look for areas where the old caulking has failed, revealing the gap between the window or door frame and your home's siding. Inspect the threshold under each door, looking for daylight or other obvious signs of an opening that is too big and needs to be sealed shut. Make sure that the weather stripping around the windows and doors is in good condition, making note of any damaged weather stripping that needs to be replaced.
2) One way to detect these air leaks is to conduct a "smoke test." To do this, you will need to close all the windows and doors in your home and turn off furnace or water heater. Next you will need to turn on the kitchen and bathroom exhaust vents, which will create a negative pressure in your house that sucks outside air into your home through any crack or opening.
Now you can check for air leaks by holding a lit incense stick close to the spaces around the edges of your home windows and doors, looking for a noticeable change in the smoke rising from the lit incense stick. If there is a air leak, the smoke will waiver and be drawn inwards by the outside air that is finding its way into your home. If the smoke remains undisturbed, then you can assume that there are no air leaks in that specific