Warmer seasons are the time to check for any air leaks in your windows.
On a windy day, hold a candle flame close to the window seams on all your windows. If it wavers, then you have an area that needs sealing up.
Outside caulking can dry up during the warmer months. Check to see if any needs replacing.
Tap the panes where the leakage is. If they're loose and rattles, then you need to replace the glazing