Heat pump in cold weather

Thomas Simon has been trying to cut back on fossil fuels. He weatherized his home and added a wood stove. But in the dead of a Vermont winter, Simon still had to rely on an oil burner to get through those cold nights and days.

But now he has found something that suits his environmental beliefs and is much easier on his household budget: heat pumps.

Once an expensive add-on that did not work well in cold climates like New England’s, heat pumps have gotten a technological makeover. The new generation of machines can keep a backwoods home warm even in extreme conditions — some to as low as 20 degrees below zero. And though they are powered by electricity, which is usually a very expensive way to heat a home, the new heat pumps are so efficient that they cost much less to run than a conventional oil heat system.

“We’re estimating that this should save us about , 200 a year, ” Simon said as workmen were preparing to install three cold-climate heat pumps at his home in Putney. “The electric will be higher, but the savings over oil should be significant.”

The new heat pumps work so well that environmental groups are pushing them as a high-efficiency supplement to or replacement for oil-burning systems and conventional electric heaters. Many utility companies offer rebates to help soften the installation costs.

Indeed, sales have been climbing steadily over the past few years since manufacturers have improved the various components — including refrigerants, compressors, and heating coils — that deliver heat from an outdoor pump.

They’re becoming especially popular in rural parts of New England, such as the Berkshires, where many homes live well off the networks of pipelines that deliver low-cost natural gas for heating.

Indeed, Massachusetts and Vermont each have programs that help consumers switch to heat pumps.

“A lot of people are familiar with air-sourced heat pumps as a technology that’s often used in the South, where they don’t get temperatures below freezing, ” said Peter McPhee, who is leading a study of heat pumps for the Massachusetts Clean Energy Center. With “a few tweaks” to those old models, McPhee said, some manufacturers have made heat pumps that can stand up to the coldest weather New England has to offer and still operate at peak efficiency.

One big improvement that has allowed heat pumps to function in cold climates is the introduction of variable-speed motors. These save energy by running more slowly — but not shutting off — when the house is at a comfortable temperature.

“A lot of older equipment is either on or off, ” McPhee said. “It would be like driving a car by either flooring it or putting it in idle. It makes it less efficient.”