Small update: Our water heater is only a 40-gallon tank. :) *I* misread the side of the tank to come up with the 79-gallon number. We can easily find a 40-gallon tank, and much cheaper too. And if we go with the 50-gallon tank, it's not a downsize, it's an upgrade!! Also we have offers of help to install it. Whew...now to make plans.