Brian DeGidio admits he hasn't thought much about the environmental benefits of the air-source heat pumps he's working on atop a large apartment complex under construction in St. Paul.

It's a drizzly Friday and DeGidio is hooking refrigerant lines to condensing units that look like window air conditioners lined up across the roof. Greenhouse gas emissions aren't top of mind.

But the HVAC system he's working on swaps fossil fuels for cleaner electricity, and DeGidio is part of a quiet revolution underway in Minnesota as the state chases ways to cut global-warming gases. Buildings — and the fossil fuels to heat and cool them — are a big overlooked source of the heat-trapping gases.

"Things will be evolving more toward this, I'm sure," said DeGidio, with Wenzel Heating & Air Conditioning.

Electric heat pumps are gaining new traction in cold-weather states such as Minnesota thanks to recent advances in the technology. The systems can now heat when it's as cold as minus 22F — and even lower in at least once case, said Ben Schoenbauer, senior research engineer at the St. Paul nonprofit Center for Energy and Environment. They're getting more economical and are seen as a front-runner in decarbonizing northern buildings.

"It's only in the last 10 years the technology has advanced to the point where you can do it for really cold temperatures," Schoenbauer said.

It's the way the industry is going, said Jacob Wise, a manager with Auer Steel & Heating Supply Co. in Plymouth: "It's grown into a huge part of our business in the last 10 years."

To speed the shift, state lawmakers are considering expanding utility rebates to install the pumps. They also want to set ambitious statewide goals for getting all new commercial buildings and large apartment complexes to net-zero emissions.

The movement is a sea change, said Minneapolis architect Elizabeth Turner of Precipitate Architecture.

"Five years ago it was difficult to find someone who would install a heat pump here," Turner said. "And now I'm seeing neighbors on neighborhood social media recommending multiple contractors for installing heat pumps."

Modern electric heat pumps have been around since at least the 1940s. They use electricity and equipment to expand and compress a refrigerant to transfer heat from the air, the ground (think geothermal systems) or water into a building for heating and cooling. Air-source heat pumps are the most common.

For single-family homeowners with a furnace running on cheap natural gas, the systems can be more expensive to operate but can cut greenhouse gases by at least half. Owners of large buildings such as apartment complexes, however, can see significant savings, HVAC professionals say.

With the higher price of propane, heat pumps have taken off faster with homeowners in rural Minnesota.

The state's 40-plus rural electric co-ops have promoted them for decades — largely for the cost savings, said Steve Kosbab, energy services manager for Meeker Cooperative Light and Power Association in Litchfield. Kosbab says nearly 1,200 of his customers now rely on them. He estimates homeowners who have relied on propane can save 40 to 60% on heating and cooling with a heat pump.

"Then there's the environmental benefits of it as well as our electric grid keeps getting cleaner," Kosbab said.

But according to Richard Graves, director of the University of Minnesota's Center for Sustainable Building Research, cheap natural gas and a building industry that has resisted change have been major roadblocks to faster adoption. If the goal is getting heat pumps in all new construction and retrofitting existing ones, Minnesota is not even in the first inning of the ballgame, Graves said.

There are other challenges. Despite significant improvements in heat pumps, most buildings require a backup heat source during Minnesota's severe cold snaps. Some new systems can run down to minus 30F, said Schoenbauer, but performance is reduced at lower temperatures.

The advances can't come fast enough.

Buildings generate an estimated 12% of the state's greenhouse gas emissions, according to the latest state inventory. If Minnesota wants to hit its legislated targets for cutting the gases — goals the state is missing by a wide margin — people must reduce the amount of fossil fuels burned for heating. From 2005 to 2018 greenhouse gases rose 32% in the residential sector and 15% in the commercial sector, according to the inventory.

In fact, Minnesota is one of the Top 10 states for greenhouse gas pollution from buildings, according to the Rocky Mountain Institute, a Colorado organization focused on energy efficiency.

"It's a big problem and one that doesn't get nearly enough attention," said Tim Schaefer, head of the nonprofit Environment Minnesota Research & Policy Center, which recently issued a report on it.

Measures in the Legislature would help speed conversion.

The ECO Act, for example, would allow utilities to offer more rebates to customers installing heat pumps. Right now they can only give them to customers who already use electric heat, such as electric baseboard heat, because utilities aren't allowed to encourage fuel-switching.

The measure enjoys broad support among utilities and conservation groups, but propane dealers aren't happy.

"It would harm our members and the residents of rural Minnesota who rely on propane," said Dave Wager, executive director of the Minnesota Propane Association. "Minnesota needs fuel choice. If the grid goes down, propane is still there."

A second measure would update Minnesota's building codes, creating new standards for all new commercial and large multifamily residential buildings to have net-zero carbon emissions by 2036. That involves cutting gases outright as well as offsetting them.

Right now only a dozen or so large commercial building in Minnesota use heat pumps. Examples include the Bagley Outdoor Classroom at the University of Minnesota-Duluth, a dormitory at Wolf Ridge Environmental Learning Center near Finland, the St. Louis County Government Services Center in Virginia, and the Rose and Hook & Ladder apartments in Minneapolis.

The proposed new codes are a modest step. Even if all new commercial construction meets them, that's a fraction of existing commercial buildings, said Ben Rabe, director of building performance at the research and advocacy group Fresh Energy in St. Paul.

But it's a start, Rabe said: "This is just one piece of the puzzle."

Jennifer Bjorhus • 612-673-4683