Our house is about 20 years old. It was built with Gapco double pane windows. A couple of days ago something hit the outside of the double living room window and broke one the outside panes of glass. How do I go about getting the glass replaced?
Thanks

Shop around. Get some extimates. I'd start with acking friends locally. Perhaps something in a HomeDepot/Lowes kind of thing. The entire unit (both panes) will have to go. This is the time to think about modifying/home improvement. Ask yourself: "Is this a window we like... right size, does it open to allow a breeze. I had to replace the siding on my house and took the opportunity to replace three windows with more efficiant windows. BONUS! They reduced the sound allowed into the bedrooms where they were installed! Lots to think about.

It may be an option to just remove the glass via from the outside, if it is a wood sash, you may be able to remove the glazing from the outside and replace the glass and reglaze, but if the window is a insulated glass you'll have to replace the sash,
Id tell you to measure the sash but if you've never done it before you may get the wrong info to give to Lowe's or homedepot, either call a window replacement company or take the sash to Lowe's or homedepot,