The Freewatt in-home system produces heat with a generous helping of electricity on the side. When a house needs heat, a natural-gas-powered Honda engine produces up to 12,000 Btus and feeds them to an Energy Star–rated furnace or boiler. At the same time, the engine spins a generator that produces 1,200 watts of electricity. You end up buying less power off the grid or, in some cases, selling it to the utility. At about 48 decibels, it’s reportedly quieter than a refrigerator.
Estimated cost with installation: About $20,000; Freewatt