Photos: San Francisco's greenest home?

The entry level opens to a spacious, blue hot tub with garden views and a sauna several steps away. The water and radiant-floor heating are fed warmth via rooftop solar panels. Hot water is stored within 150 tubes and a 450-gallon tank.

Lochinvar Knight provides an energy-efficient boiler that serves as backup to the solar heating system. A tankless, on-demand water heater from Takagi also reduces energy waste up to 80 percent, according to Wilson.