Vermont Energy Investment Corp. has outgrown its 30,000-square-foot office on Burlington’s South Champlain Street. This spring, VEIC is moving into a far larger space in the former General Dynamics building on Lakeside Avenue — now dubbed the Innovation Center of Vermont.

VEIC executive director Scott Johnstone confirms that a lease was signed in December, and that the energy nonprofit’s 200 employees will relocate sometime between April and June. The move is a major score for Pomerleau Real Estate and the Michigan-based owners of the South End building, which lost its namesake tenant last year when the defense contractor moved to the IBM campus in Williston. The departure left 167,000 square feet empty in the four-story, brick building.

VEIC operates Efficiency Vermont, the nation’s first statewide energy-efficiency utility. Its headquarters are in Vermont, but VEIC has offices in Ohio, Boston and Washington, D.C., where it consults with area utilities on energy-saving strategies. The nonprofit also has done work abroad.

Johnstone says the move will allow VEIC to consolidate operations under one roof — the company has a smaller office in the Cornerstone Building at Main and Battery streets — and minimize administrative costs. In its current office, the company has four different leases, each with a different rate, as a result of incremental expansions, according to landlord Jason Adams of Adams Real Properties.

The new offices will occupy 50,000 square feet on the fourth and fifth floors of the Innovation Center.

Since moving into its South Champlain quarters 13 years ago, VEIC has grown exponentially. In the three years Johnstone has been at the helm, it’s added 35 employees; Johnstone says the staff now numbers “about 200.” Publicly available tax records from 2008 show the company reported close to $38 million in total revenues, which come from a variety of fee-for-service energy programs.

Thanks to geothermal cooling and state-of-the-art energy systems, the U.S. Environmental Protection Agency considers the Innovation Center to be one of the most energy-efficient structures in the country. That doesn’t mean VEIC won’t try to button up the place even more.

“We’re working with an architect to see what else we can do before we move in there,” Johnstone says. “We expect that space will be highly energy efficient, hopefully surpassing where we are now.”

VEIC is the largest tenant by far in the Independent Block, says Adams. He tried to accommodate the nonprofit — and even considered adding to the north end of the property — but determined it would take too long to meet the company’s needs. Numerous smaller tenants share the building, including Seven Days, WIZN-FM/The Buzz, QuantaSpec and Vermont Wine Merchants.

“It’s gonna hurt us,” Adams says of the coming vacancy, “but with the kind of building it is and the location, I think we’ll have a good opportunity to get a bunch of smaller companies.”