As the country emerged from the Great Depression in 1937, Nashua native J. Lawrence Hall decided to open a heating and refrigeration service in the city.

A mechanical engineer by trade, Hall converted his Chevy Roadster into a pickup truck for service calls and set up shop in a modest office on Pearson Avenue. The oil heating and refrigeration industries were new in those days, so Hall was a pioneer.

More than 75 years later, the J. Lawrence Hall Co. is a third-generation family business that designs, builds and installs and services HVAC systems for commercial and industrial customers. With each generation, the company has multiplied.

“My grandfather started with just himself,” said Charlie Hall, of Nashua, now company president. “Maybe we had 10 people when my father took over, and we got it up to 30 with my father here. Now we’re at 65.”

Business isn’t the Hall family’s only pastime; community service is another. Charlie Hall is president of the Rotary Club of Nashua. His father and grandfather before him were also Rotarians. Charlie has volunteered for the YMCA of Greater Nashua and Nashua’s Adult Learning Center, and he was instrumental in developing Conway Arena, Nashua’s public hockey and ice skating facility.

In the early days, it didn’t take long for J. Lawrence Hall to make a name for himself. By 1945, the business had outgrown its modest Pearson Avenue space. Hall moved the company to 11 Main St., where it remained until the 1980s.

Hall’s son Phillip joined the company in 1951, after earning his bachelor’s degree in mechanical engineering from the University of New Hampshire and serving four years in the Air Force. He took over around the late 1960s or early 1970s.

The company expanded again in 1983, moving to 10 Cotton Road. That was around the time that Phillip’s sons, Charlie and Elliot, got involved. Charlie worked on the business end of things, while Elliot focused on engineering. In the mid-1990s, the brothers took over.

Charlie, 54, and Elliot, 56, ushered in a period of rapid growth. They added sheet metal fabrication and started a plumbing division. Two years ago, they moved the company again to a larger facility at 17 Progress Ave., and in the last two years, sales have increased 20-25 percent.

“We’ve got pretty consistent growth going on,” Charlie Hall said. “But it has been fairly controlled, not out of hand. … We try to do a conservative approach.”

The jury is still out on whether the fourth generation will eventually take over.

“That’s yet to be seen,” Hall said. “We certainly hope so.”

Either way, the company has a group of long-term employees that feel like family. A couple of them have been with the company 40 years, Hall said.