Another good way to save energy on water heaters is to use tank less on demand water heaters. You can find them online, or sometimes at Home Depot. Since these systems may not be adequate during a shower, it would be good to connect the plumbing in series, this way the output water of one unit feeds input of the next unit. You will need to have an electrician and the utility company wire in more separate heavy duty circuit breakers. Having the home wired for more heavy duty circuit breakers may seem counter intuitive to saving energy, but the energy used by these units is spent for a short time at over 95% efficiency; where as the regular tank units waste considerable amount of energy by radiating heat (due to low insulation) during idle hours. Talk to your local PHYSICS professor to verify this, and not your local numb nut handy man.