Lawrence, Mass.
Green bona fides: Monarch Lofts has one of the largest residential geothermal heating and cooling plants in the United States.
Twenty wells sunk deep into the earth contain water that remains 50 to 55 degrees year-round. Heat pumps, which act like refrigerators, transfer heat from the water in winter and cold from in hot weather.
No fossil fuels are directly consumed, but the heat pumps do draw electricity. The savings on utility bills total 25 percent to 50 percent. And because no fossil fuels are burned on site, there is no exhaust.
Other green features: The building has rooftop gardens and a private park that has a small lawn but uses water-efficient native plants.
The building itself is recycled. It was once the world's largest textile plant, the Wood Mill, where wool was spun into worsted fabric. When the textile industry abandoned New England for points south and overseas, the mill went dark.
Prices: From $189,000 for an 868-square-foot studio to $499,900 for a 2,063-square-foot penthouse with an 800-square-foot private roof deck. The 6,000-square-foot penthouse costs $1.5 million.
For further info: Monarch Lofts 
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