This 'cold' gym is kept as low as 45 degrees Fahrenheit inside to help you burn more calories

The studio at Brrrn. 

The average October temperature in New York City is 63 degrees Fahrenheit, but it's much colder inside Brrrn, a 3,000-square-foot fitness studio that opened in Manhattan this May.

Brrrn is the world's first cold-temperature fitness studio. Inside, the temperature is kept anywhere from a brisk 45 degrees to 60. Owners Jimmy Martin and Johnny Adamic say the cold air during exercise helps you burn fat and more calories.

Inside Brrrn studio. 

"When you exercise in cooler temperatures, you optimize the fitness experience, because you burn more calories than in ambient or hot. You burn fat, you can grow a tolerance to cold, and cooler temperatures provide the optimal temperature for working out," Adamic, a nationally-certified trainer with the National Academy of Sports Medicine, tells CNBC Make It. "Heat can limit your body's ability to perform at its best."

Brrrn is located in Manhattan's Flatiron District, in an area dubbed "Fitness Alley" because of the close proximity of Barry's Bootcamp, Flywheel, YMCA, Rumble Fitness, Equinox and other studios. The studio has a 1,300-square-foot workout space, showers, lockers and a communal eight-seat infrared sauna.

It offers just three fitness classes: Hit, a high-impact, strength training class using dumbbells and a battle rope with the temperature set at 45 degrees; Slide, a core and cardio workout at 55 degrees; and Flow, a yoga and mobility-inspired class at 60 degrees.

Though Slide and Flow are not set at the chilliest temperatures, they are still cold. To put it in perspective, the average November temperature in New York is 52 degrees. According to Brrrn, fitness studios traditionally operate between 72 and 110 degrees.

"It's just as safe to exercise in a chilled studio as it is in a room temperature class," Nayda Swedan, MD, FAAPMR, a physical medicine and rehabilitation specialist for sports injuries tells Men's Health. "You can actually burn more calories working out in the cold because your body is not only exercising, but it's also working to raise your core temperature, so it's working harder. Research has shown that the heart and lungs both have to work harder in colder temperatures."

A 2017 study found that people who hiked in 15 to 23 degree temperatures burned 34 percent more calories than those who hiked when it was 50 degrees.

Brrrn encourages the use of the infrared sauna after class because it helps improve blood circulation, relieves pain and relaxes the body. Infrared saunas are known to heat the body more directly and deeply than traditional 185 degree stove-heated saunas. Infrared heat penetrates more deeply than warmed air, even at 140 degrees, offering the potential of a more vigorous sweat at a lower temperature.

Brrrn owners Jimmy Martin and Johnny Adamic.

Martin, a former personal trainer, said he'd been playing with the concept of a cold-temperature fitness studio for a while, but it wasn't until he lost his wife to cancer at age 29 in 2014 that he "gave full attention to making this dream a reality."

"Months later I met Johnny," Martin tells CNBC Make it. "Learning about his background and passion for health and wellness, I knew without a doubt that this was finally going to happen with the right person."

Adamic had already been researching the benefits of cold-temperature fitness. He also had substantial experience in public health, having worked at New York's Department of Health & Mental Hygiene in the Bureau of Chronic Disease Prevention and Tobacco Control, as well has having served on then-Mayor of New York Michael Bloomberg's Obesity Task Force.

Hit class at Brrrn. 

A single Brrrn class is $34, slightly cheaper than the offerings at SoulCycle and Barry's Bootcamp, which each cost $36.

Since opening, Brrrn's success has surpassed the two men's expectations. "We've been seeing 30 percent growth in new customers each month since May," says Martin. "Equally if not more important is our retention within our customer base — 30 percent of our first-time customers have returned a second and third time."

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