The matter of mastering a building's energy use, getting maximum performance out of each calorie and electron, is to many people a black art. Experts say that applying energy efficiency to this area could make major reductions in greenhouse gas emissions, but actually achieving these savings is hard for a variety of reasons. For one, renters are often the people nearest the thermostats, and they have little incentive to turn them down, or up. Paying heating or air-conditioning bills is usually the landlord's job. Even for landlords, the incentives and the tools to measure and save energy may not be there. That's where Steve Heinz comes in.