I do know that I watched my natural gas bill for the year prior to the installation and a year after the installation and saved an average of $20 a month after the install. That is $240 a year. Since the unit is now nearly 5 years old, it has nearly paid for itself, not to mention the $1500 tax credit in the initial tax year. I also use the recirc timer to turn on at 6 AM for morning showers, and again at 10 PM for nightly face washing, washing dishes, and occasional showers. Not a drop of water is wasted because the water just circulates within itself.