Drafty windows make it harder and less efficient to heat and cool a home throughout the year. Windows are not maintenance-free, but with regular cleaning, caulking and glazing they can be kept in good condition.
Check for Drafts
Determine if air is flowing through your closed windows. During cold weather, drafts of cold air may be obvious. An easy way to identify drafts regardless of the season is to hold a lit candle close to the window seams on a breezy day. If the flame bends, it signals air movement pushing through the window from outdoors.
Check the caulk on the outside window frame and the glazing around all of the panes. Exterior caulk can dry out in the heat of summer and cause gaps and cracks which let air and water into your home. Window glazing needs to be replaced periodically, as the putty ages, its seal along the glass loosens. You can often tell if glazing needs to be replaced when you tap on a pane of glass and it rattles in its setting.
Scrape Away Loose Glazing and Old Caulk
Use caulk softener to help remove the old caulking. Apply it at least two hours in advance to give it a chance to soak in so it will come up fairly easily using a putty knife. Remove as much of the old caulk as possible to ensure that the new caulk will adhere properly and give the window a good seal.
Use a putty knife to check for weak glazing too. Remove any hardened glazing that flakes away easily.
Install New Glazing
Clean the surfaces where you’ve removed old glazing and the glass pane. The glazing will need a dust-free surface on which to adhere.
Window glazing comes in either small tubs (to be applied with a putty knife or paint scraper) or a tube (to be applied with a caulking gun). The tub of glazing works best for small areas because by using a paint scraper, you can really compress the glazing into position for a tight, compact seal.
Use a tool to scoop out a small bit of glazing to create a smooth slope along each pane of glass at roughly a 20- to 45-degree angle to the base of the window pane. Work the glazing until it is smooth.
Re-glazing windows requires a longer dry time (and extends the project timeline from a few days to a few weeks). Paint over the glazing once it has hardened.
Apply New Caulk
One tube should be enough to seal a whole window. To begin, cut the tip off of the tube of caulk at a 45-degree angle so that the tip will fit nicely into the window seam. Apply the caulk by moving the gun along the seam in a smooth motion while squeezing the tube with even pressure. When filling larger gaps, move more slowly to let the caulk adequately fill the space. Finally, use a wet finger to smooth out the caulk and give it a clean, finished look.
Give the caulk 12 to 15 hours to dry and set, and then your windows should be airtight for the season.
Source http://www.diynetwork.com/how-to/rooms-and-spaces/doors-and-windows/how-to-check-and-seal-windows
