If you find yourself replacing those old (and likely inefficient) windows with newer ones, the old windows can be part of the most efficient means of recycling there is: reusing. Keeping in mind the old adage "one man's trash is another man's treasure," your old windows may be the perfect addition to someone else's shed, greenhouse or other project. And thanks to the popularity of using recycled building materials in the home, most large cities have at least one place to donate these types of materials.
Locate a collection centre for used building materials. Many larger cities have a Habitat for Humanity Restore resale outlet that accepts building materials it can sell to fund Habitat for Humanity's various projects. Some towns have other non-profit building supply centres, like Portland, Oregon's Rebuilding Center. You can often find information about charitable and commercial rebuilding centres by contacting your local waste management office or by searching the online database at Earth 911.
Once you've found the collection centre nearest you, note its drop-off times and get driving directions. Many collection centres, especially those run by municipal governments, have only specific days and times you can drop off materials.
Package the windows for transport, taking care not to break the panes of glass. If the windows are very old, they could contain lead, which can be hazardous to your health even in small amounts. Wrap the windows in large moving blankets or packing material for safe transport to the collection centre.
Drive the windows to the collection centre on the appropriate day. If you are donating your windows to a charity like Habitat for Humanity, be sure to fill out a tax receipt with a worker at the drop-off centre, since you will be able to use the donation as a tax deduction.
Replacing your windows for more efficient ones can save you money on your utility bill each month. It can also earn you credits on your taxes for the donation of your old windows to a charitable organisation plus a federal tax credit for energy efficiency.