It’s hard to miss the gold-plated dome atop the Colorado State Capitol, but the nearly invisible geothermal system that heats and cools the building is every bit as compelling.

Operational since 2013, the system was a first for a state capitol building.

“The building is uniquely situated over the aquifer in downtown Denver,” says Doug Platt, the capitol’s spokesperson. “The way our geothermal system works is it pulls the water out from underground, circulates it through a variety of heat exchangers throughout the building, and then we put the water back into the ground so that there’s no net gain or loss of the water from the water table. We just borrow its temperature: a constant 64 degrees underground.”

Notes Platt: “It’s a more moderate baseline to both heat and cool the building.”

Designed with a target reduction in energy costs of $29 million, the geothermal system “pays for itself with energy savings,” he adds. “Should there not be energy savings demonstrated, the builder of the system has performance contracts where they would offset if there was any increase in cost. At the end of the day, the system was built with no state tax dollars.”

Geothermal heating and cooling is not the capitol building’s only superlative when it comes to sustainability.

“The Colorado State Capitol was the first one ever to get LEED-certified,” says Platt.

The implementation of recycling and water conservation programs and a move to energy-efficient LED lighting helped garner the certification from the U.S. Green Building Council, he adds, noting, “We have converted over 22,000 lights not only in the capitol, but in the entire Capitol Complex.”


The biggest sustainability challenge at the capitol involves bringing a building built in the 1890s into the 21st century.

“With the technology that’s hardwired into the building, sometimes it makes it a challenge to do that, but that doesn’t deter us from doing a lot of common-sense things as well as technologically advanced things,” says Platt.

“Despite the fact that you don’t see this stuff as a tourist, a lot of its going on in inconspicuous areas,” he continues. “We need to always consider the architect’s vision of the building and the historical significance of the building so that when we do these things, we don't disrupt that historic character. Putting in a geothermal system, for example, we didn’t run new ductwork where people can see anything. It all has to be done without disrupting the historical vision of the building.”

Gov. Jared Polis has also promoted sustainable practices via executive orders, including one in 2023 that established a sustainability office to promote government efforts and reduce energy and water consumption in state buildings.

It also pushes the greening of the grounds at the capitol and other government properties.

“This executive order talks about xeriscaping, it talks about converting all of the equipment that we use to landscape from gas power to electric power,” explains Platt.

All of these initiatives add up to a significant whole. “When we talk about sustainability, it’s sort of a journey rather than a destination,” says Platt. “We’re walking the walk.”


Take a free tour of the capitol building, Monday through Friday, where you can admire the intricate stained glass, towering columns, gilded crown molding, gleaming brass chandeliers and, of course, the gold dome atop it all.