Mini-split heat pumps were a major topic at the Northeast Sustainable Energy Association (NESEA) BuildingEnergy 14 conference in Boston this year, and with good reason: Heat pumps have grown beyond their roots as a southern-state solution and are making in-roads in cold climates from Idaho to Minnesota to Maine.Heat pumps don’t use electricity to create heat; they simply transfer heat from outdoors to indoors (or vice versa). In mild climates, where the difference in temperature between inside and outside the house is relatively small, heat pumps are a no-brainer. As the air gets colder, though, air-source heat pumps lose capacity....

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