For many Minnesotans who long have held out against air conditioning, this is the summer they joined the crowd.

A second uncomfortably warm July in a row prompted a run on central air-conditioning systems, keeping installers busy and even helping to drive one-day electricity use to a record high for a northeastern Minnesota utility that previously had seen records only in the winter.

In the Twin Cities, air-conditioning installations for one company were up 40 percent compared with 2010, when a federal tax credit boosted business.

"They call and say they can't take it anymore," said Scott Spanjers, sales manager at Twin Cities Plumbing, Heating and Air Conditioning. "We've broken the spirit of true Minnesotans that can take anything."

Same for Corrin's Plumbing, Heating and Air Conditioning in International Falls, aka Icebox of the Nation.

"People are thinking this is what's going to happen every summer now," said controller Jerry Kustiak. "It used to be we'd have a few hot days here, a few hot days there. This summer it's been every day. They're sick of being hot."

Customers of Minnesota Power, a utility serving northeastern Minnesota, used more power July 16 than on any other day in the company's records -- 8 percent more than normal for the date. Peak usage for the company always has been in the winter; the July 16 mark broke the old single-day record set in January 2011. It exceeded that mark by only one megawatt, but spokeswoman Amy Rutledge said seasonal demand is likely to become nearly even year-round.

A large portion of Minnesota Power's customers are taconite mines and paper mills, whose round-the-clock demands are consistent through the year, Rutledge noted. July's peak was clearly residential and weather-related, she said.

"A lot of folks in our region say, 'Lake Superior is our natural air conditioner. Why would we need air conditioning if it's hot only two weeks out of the summer?'" Rutledge said. "But we do believe more people are retrofitting their old homes with air conditioning, and we're also seeing that with new construction, central air is really a standard. Twenty years ago that may not have been the case. Now it's considered something that adds value."

'Can't dress for the heat'

July tied for the warmest on record in Duluth, was second-warmest in the Twin Cities and warmest in La Crosse, Wis. Rochester's average daily low temperature -- most often experienced at night -- was the highest for any month on record. The previous July stood out for a number of dew point records, including the all-time high in the state, in Moorhead.

Those are some of a raft of statistics that show an overall long-term warming across the region. While the trend has been most pronounced in the winter, it's arguably been felt most keenly in summer, coming on top of customary seasonal warmth.

"You can always dress for the cold, but you can't dress for the heat," said Kustiak in International Falls.

Marketing tool

In the Twin Cities, the percentage of homes with central air conditioning more than doubled between 1985 and 2007, from 30.4 percent to 69.5 percent, according to the Minnesota state demographer.

Central air conditioning has become "as necessary to people as your kitchen appliances," said real estate agent Jude Dugan Olson, who buys and sells homes all over the Twin Cities.

Olson said prospective buyers now use air conditioning as a negotiation tool, asking sellers either to install it or cover closing costs if they are close to the cost of a new system. Meanwhile, she encourages sellers who don't have it to put their homes on the market in cool weather, or at least to have an estimate for installation prepared. Lack of air conditioning is a competitive disadvantage for comparably priced homes, she added; prospective buyers of vintage, million-dollar Twin Cities homes are often shocked to learn the homes, built in a different time and climate, and for people perhaps with different expectations, don't have air conditioning.

Air conditioning also has become a standard amenity even at Minnesota's mom-and-pop resorts. Fifteen years ago, only one of the handful of resorts around Rush Lake in Otter Tail County had air conditioners, said Aggie Pendy, who runs Four Seasons Resort with her husband, Mike. Now they all do.

Pendy said she and her husband decided to start installing window units six years ago when they spotted some pregnant cabin users periodically sitting in their air-conditioned cars to cool off.

"I've got to tell you, my Iowans and Nebraskans love the weather," she said, indicating that they have continued to regard Minnesota as a place where the weather is cooler than at home. "They say it's great to have the cabin windows open at night. When we were in that heat, Minnesotans were running those babies 24-7."

Burning energy to stay cool

Xcel Energy residential customers used only 1.8 percent more energy this July than they did last July, but that was 24.5 percent above normal. This year's peak use to date came on July 2, when the heat index in the Twin Cities hit 105, and fell just short of the Xcel record, set July 20, 2011, when the heat index reached 108.

Homes with central air conditioning use an average of 1,636 more kilowatt hours of electricity than those without it, kicking out an additional 2,800 pounds of carbon dioxide, according to the Minneapolis-based Center for Energy and Environment (CEE). Moving the thermostat from, say, 74 degrees to 76 can save 13 percent of that use. (Xcel Energy's recommended setting is 78.) The average household emits 40,000 pounds of CO2 each year, according to CEE.

Energy use was on John Gustav-Wrathall's mind when he and his partner, Göran, ordered central air conditioning for their 100-year-old home near Powderhorn Park in Minneapolis in July. But so was comfort. John Gustav-Wrathall, a paralegal who works at home and has lived in Minnesota 20 years, said he never envisioned living in an air-conditioned home. But he struggled with the heat last July, and during this July's heat wave was having trouble concentrating on his work and was worried about his computer overheating. What sealed the deal was when he and Göran were planning a dinner and game night with friends, and the friends suggested going to a different house.

"When we were the ones that said, 'That might be nice,' we knew it was time," he said. "We did feel a little guilty about it ... until we realized how nice it was."

Guilty? Gustav-Wrathall said he and his partner would rather cut down on their energy use than increase it. They don't own a car. So the new comfort came with some conflict.

"If we are experiencing some kind of global-warming phenomenon, buying more air conditioning is probably not the long-term solution to the problem," Gustav-Wrathall acknowledged. "We have some hard questions to answer."

Bill McAuliffe • 612-673-7646