It heats. It powers. Is it the future of home energy?

Down in Bernard Malin's basement is a softly thrumming metal box that turns natural gas into hot water and generates $600 to $800 worth of electricity a year - a bonus byproduct of heating his home.

"It's like printing money," says Mr. Malin, the first person in Massachusetts - perhaps in the nation - to own a residential "micro combined-heat-and-power" system, also known as micro-CHP.

But he's not likely to be the last.

Since Malin changed his home heating system to micro-CHP in February, 18 other families in the Boston area also have adopted the technology, which squeezes about 90 percent of the useful energy from the fuel. That's triple the efficiency of power delivered over the grid.