Here is the bitter truth: Windows are expensive to replace, and replacing them won’t address the biggest source of heat loss and uncomfortable drafts in your home — an under-insulated and poorly air-sealed attic.
We recommend considering window replacement only when you have exhausted all the other likely suspects for leaks and drafts.
You can address the biggest leaks and drafts in your home by insulating and air sealing your attic. This project is generally less expensive and more effective than window replacement. After that, if your windows still feel drafty, then consider reconditioning or replacing them.
During winter, hot air rises and escapes through leaky attics. Because hot air is escaping out the top of your home, new cold air is pulled in through small openings around your home's foundation, windows, and doors. In other words, the big (and largely invisible) leaks in your attic often cause that draft near a window or door.
When you insulate and air seal your attic, the heated air will remain in the living space where it belongs — which means a lot less cold air will be pulled in, putting a stop to annoying drafts
After you have proper attic air sealing and insulation, you can move on to making cost-effective window improvements. The Minnesota Department of Commerce’s Home Energy Guide offers a clear breakdown the different components of window repair and replacement — check it out in a link below.
How much will it cost to fix my windows?
If your windows have large air leaks, reconditioning is generally cheaper than replacement. Reconditioning usually runs about $150–350 per window, depending on size and type.
When you opt for window reconditioning, a contractor might perform the following tasks, among others:
Insulate the spaces between the existing window frame and house framing
Remove sash cord system and install new window tracks (jamb liners)
Groove out the sides of the existing window sashes to accept the new jamb liners
Install new weather
-stripping at the top, middle, and bottom of existing sashes
Replace loose putty or broken glass
Replacing your windows completely can run about $450 to upwards of $1,200 per window (oofta!), and can result in minimally better energy savings than reconditioning. These two reasons are why replacement should be your last resort.
Home Energy Guide
On page 21 of this guide there are details on window repair and replacement.