AUGUSTA — Gusty winds rattled the master-bedroom windows in the 181-year-old Blaine House during last winter’s sub-zero cold snap, but Gov. Paul LePage said he never had to turn on the oil heat. The governor’s sleeping quarters, while poorly weatherized, were kept warm by a high-efficiency electric heater that doubles in summer as an air conditioner.

Now, workers are installing 22 more of those units in the governor’s mansion.

“After this winter, it was phenomenal,” LePage said. “I’m sold on them.”

LePage is hot on ductless, air-source heat pumps, which are emerging as the fastest-growing energy alternative in Maine. From nearly zero two years ago, more than 5,000 have been installed, according to Efficiency Maine.

The latest versions can warm homes and small businesses at less than half the cost of heating oil.

On Thursday, the governor and his energy advisers offered the Portland Press Herald and the Kennebec Journal an exclusive tour of the project.

The units are getting a high-profile stamp of approval from a political leader who has been at odds with environmental groups about shifting state efficiency dollars from reducing electricity waste to funding cheaper sources of heat. And while LePage said he’s embracing heat pumps, he’s also encouraging residents to use state rebates for high-efficiency propane, natural gas and wood-pellet conversions.

“What we’re trying to do is lower the cost of heat for Maine families,” he said.

Efficiency Maine offers $500 rebates for homeowners who buy heat pumps. Small businesses also have a rebate program. Much of the $7 million in the home energy savings program comes from the state’s share of the Regional Greenhouse Gas Initiative and is available first-come, first-served.

“I think it really shows that this new technology is going mainstream,” said Michael Stoddard, executive director of Efficiency Maine, an independent trust that promotes energy efficiency. “We’re putting them in apartment buildings, and we’re putting them in the Blaine House.”

The heat pumps are sometimes called “mini-splits,” because one part is indoors while the other is hung or mounted outdoors. They use refrigeration technology to extract heat from outdoor air. In the summer, they work in reverse to provide air conditioning.

The devices are popular because they cost about one-third as much as a central heating system. They come in various sizes; typical retail prices for single-zone models range from $3,000 to $5,000. Depending on how big a home is and how well it’s weatherized, a unit can satisfy 50 to 75 percent of year-round demand.

The work underway at the Blaine House is part of an effort this year to convert heating systems in state-owned facilities in the capital, mostly from oil to natural gas. The conversion will displace 1.1 million gallons of oil a year and pay for itself in energy savings in about two years, according the Bureau of General Services.

The Blaine House was a good candidate for a heating system makeover. The oil boiler in the basement was installed in the mid-1990s. It guzzled 5,074 gallons of fuel last year at a cost of $16,775.

The boiler’s burner will be converted this summer to burn natural gas. It doesn’t make financial sense to buy a new, high-efficiency gas boiler, said Jim LaBrecque, chief technology officer of Flexware Control Technology in Bangor, because gas will be needed only on the coldest days.

The basic contract for the heat pump installation is about $68,000, plus some related building repairs. Along with the natural gas conversion, the total heating upgrade is expected to cost $115,000.

Workers from Augusta Fuel Co. are busy completing the project. On Thursday, they were involved with the refrigerant lines connecting the indoor and outdoor components. The outdoor compressors are behind the mansion, hidden amid shrubbery. One goal, LeBrecque said, was to remove the 26 window air conditioners that protruded each summer from the historic public building. Indoors, the heat pump “heads” are mounted on walls or floors. They are appliance-like, louvered boxes that could be mistaken for any common heating or ventilating units. On Thursday, the heat pump in the governor’s staff room was quietly emitting cool air, welcome on the warm morning.

Stoddard noted that Efficiency Maine’s website has a searchable link for approved installers in Maine, and said people should shop around for the best deal and service, as they would for any appliance.

“We want people to have a good experience,” he said.