We are just starting to get rough estimates on some of the products we are hoping to install.

Windows: replacing seven windows with energy efficient models will cost us about $750 per window, or $5200.

Water heater: replacing the old water heater with an on-demand system - a nice Bosch unit at Home Depot costs about $1,000, and we estimate about $300 for installation.

Boiler: it is hard to find specifics on these through the Internet for some reason, but it looks like we could expect to pay $2500 for a new model installed. Also, several websites said that if your current unit is not too old, and it isn't over sized for your home, you may not want to worry about it. I need to research that a bit more.

Total:
Windows          $5200
Water heater   $1300
Boiler                $2500
Grand Total     $9000

Factor in the $500 tax credit for the windows, and that's about $8,500 to potentially reduce our household carbon emissions by 15%.