This old house: It wasn’t green when I bought it two years ago. It had single-paned windows, a heat-pump-style air-conditioning and heating system and all incandescent lights. It was so 20th century.

First green renovation: The first thing I did was replace the incandescent light bulbs. I switched to compact fluorescent light bulbs, or C.F.L.’s.

Next big purchase: Double-paned windows, which I think will cut down my heating bill by half. The windows will cost more than $20,000.

Image Bill Nye, the television host and science educator. lives in a retrofitted, eco-friendly, 1,300-square-foot, 1939 stucco home in Los Angeles. Credit... Emily Shur

Eye-opener: I’ve got a grapefruit and an orange tree in my backyard, and if you care for them, they produce like crazy. My neighbor lent me her juicer, so I have fresh-squeezed juice every morning.