For more information about heat pumps and rebates: www.efficiencymaine.com.

LEWISTON — Brian Babbidge was interested but skeptical about heat pumps as a green and inexpensive way to heat his home.

“I did a lot of research on it,” he said. “I did not want to throw my money away.”

Most heat pumps sell for about $3,000 and qualify for a $500 rebate from Efficiency Maine, Babbidge discovered.

“I insulated my attic to keep the heat in,” he said.

He had a heat pump installed this past summer.

“I’m very pleased with it,” Babbidge said. “It works.”

He said he’s burning a lot less oil. He turned on his oil-fueled heat for the first time in December.

“My electric bill went up only $8 to $10 a month,” he said. “I’ll pay that before paying the oil guy. Plus the heat pump air-conditions my whole house in the summer.”

Mark Grenda put a heat pump in his Bridgton store a few years ago. Now on his third winter, he considers heat pumps one of the greatest inventions.

“It’s great. It’s quiet, efficient,” Grenda said.

After his rebate, his heat pump cost about $3,000. It’s saving him money on winter heating and summer cooling, he said. He’s burning less oil.

“You should get one,” Grenda said.

Heat pumps are taking Maine by storm, said Dana Fischer of Efficiency Maine, which offers $500 rebates for one heat pump, $750 for two.

“Heat pumps are being installed in Maine faster per capita than any other state I’m aware of,” Fischer said. It’s a phenomenon, he said. Like Maine, “Nova Scotia is going through this. There’s been a huge influx of units. The trend is exciting.”

In the past year, 5,000 heat pumps have been installed in Maine homes and businesses, Fischer said. Based on the number of rebates paid out, there are about 22,000 heat pumps in Maine.

At the rate they’re being installed, Fischer expects there’ll be 50,000 units in Maine over the next five years. Business and homeowners who have them “love them,” Fischer said.

“When we ask people to rate them 1 to 10, they’re almost always 9 or 10,” he said. “People hear and see about heat pumps from their neighbors. It’s word of mouth.”

But not everyone loves them.

Roger Caron of Lewiston has two heat pump units, one upstairs, one downstairs. He’s not thrilled.

“The air-conditioning parts work pretty good,” Caron said. “It does a good job dehumidifying.”

But he’s not happy with the heat.

“It puts out heat, but for us, it’s not enough,” he said.

The heat pump works like a wood stove, Caron said. In the room with the heat pump, it’s 75 degrees. “At the other end of the house, it’s 66 degrees.” That’s not freezing but it’s not comfortable either, he said.

The salesman did a good job of selling it, Caron said, adding that the two units cost about $8,000.

“We spent a lot of money,” Fischer said. “You have to have an open concept for it to work well.”

Heat pumps are not central heat, he said.

How much heat they provide depends on the size of the home and how well-insulated it is. For a small- to medium-sized home with good insulation, one heat pump may do all or most of the heating, except when temperatures dip very low.

Experts recommend having a backup heating system for when it gets very cold. But Fischer said heat pumps not working well in extreme cold “is a myth we’re trying to overcome.”

If you want your home to be 70 degrees in the winter, you have to set your heat pump higher than 70, Fischer said.

Heat pumps are inexpensive and highly efficient, Fischer said. It’s one of the cheapest ways to heat your home, he said, short of a homeowner who gets free wood to burn in a wood stove.

Heat pumps use electricity to run, but the heat is not electric; they extract heat molecules from the outside air — yes, in the winter — and turn them into heat inside a building.

Another big advantage is there’s no combustion, Fischer said.

Josh Karkos of Karkos Heating and Plumbing in Auburn said heat pumps sales are good. And they do lower heating costs.

“I’ve been really busy,” Karkos said. “I put in 30 this summer; I have another 20 to go as of right now. Everybody’s been happy with them.”

He recommends heat pumps for the shoulder seasons. They work in the dead of winter, but he recommends a second source of heat.

Environmentalists say heat pumps are clean

AUGUSTA — In addition to being an inexpensive source of heating and cooling, heat pumps get the thumbs-up from environmentalists.

Heat pumps are a cleaner source of energy and result in less carbon pollution than heating with oil or gas, which heat the majority of Maine buildings, experts say. In fact, several Natural Resources Council of Maine staffers have heat pumps in their homes.

Heat pumps use electricity to operate. How green heat pumps are depends on the source of electricity. When using electricity from renewable sources, heat pumps are a green way to heat, said Dylan Voorhees, NRCM’s Climate and Clean Energy project director.

Solar panels on a building make heat pumps 100 percent renewable, Voorhees said. Solar panels require a big investment, often more than $10,000. Voorhees says consumers “don’t need to have solar panels to be all renewables; you can also buy 100 percent renewable electricity from a variety of sources. Those options make heat pumps among the greenest ways to heat a home.”

Much of Maine’s electricity comes from renewable sources.

Government energy web sites show that two-thirds of Maine’s electricity comes from renewable sources: hydro, biomass (wood products) and wind. The Natural Resources Council of Maine estimates that 40 percent of Maine’s electricity comes from renewable sources.

Either way, a lot of Maine’s electricity is renewable.

“Heat pumps are really an efficient energy source,” Voorhees said. The way the units take the heat from the air and generate heat in buildings means “that it’s not an injustice to say it’s the energy coming from the sun,” Voorhees said.

More heat pumps in Maine means more consumers are using less oil, which means less fossil fuel.

While many people can’t afford to invest in solar panels, heat pumps can be a good first step to cleaner energy, Voorhees said. “You don’t have to solve the whole house at once.”