It was 105 degrees — as hot as a typical steam room — at Pure Yoga on the Upper East Side on a recent Saturday, but for the 16 women already perspiring through a series of plié squats in a ballet-based barre method workout, it wasn’t blistering enough.

“We’re turning it up to 110 degrees by popular demand,” the instructor, Kate Albarelli, 31, announced in the sort of cheerful tone that would usually signal a time to rest. The women looked as delighted as if she’d given them one.

The demand for ever-hotter exercise rooms is sufficient enough that Chad Clark, a former college wrestler turned Bikram yoga instructor in Scranton, Pa., has built an entire business turning studios tropical. He recently worked with a manufacturer to design a special heater that could maintain temperatures of up to 175 degrees.