In downtown Boise, the sidewalks aren't just warm with summer heat — they're literally powered by it. Beneath the Idaho Capitol, a massive underground hot spring fuels the nation's oldest and largest geothermal heating system, The Arbiter reported.
Unlike most geothermal systems in the U.S., Boise's taps directly into natural hot water from the earth, a rarity in American cities.
"Our geothermal system is essentially tapping into a hot spring that sits under Boise — and that's unique," Amy Parrish, sustainability director at Boise State University, told The Arbiter. "It's not something that a lot of communities have access to."
Boise began harnessing this subterranean heat resource in 1982, The Arbiter reported, and it remains the only U.S. state capital that heats its Capitol building using hot water from beneath the ground. Boise State University also relies on the system to heat major buildings like the Student Union, the Center for Visual Arts, and the Administration building as part of its commitment to achieving carbon neutrality by 2050.
Today, this network quietly delivers clean, renewable energy to more than 6 million square feet of homes, offices, and schools. It's a powerful example of how legacy infrastructure can still lead on climate.
Keeping that system running, however, takes careful coordination. The Arbiter reported that this past spring, the city began a multi-month project to replace aging geothermal pipelines along 10th Street, a necessary investment in long-term reliability and safety.
As with any major infrastructure project, the work has brought temporary disruptions to nearby traffic and businesses. But once complete, the new system will be stronger and more efficient, ensuring the benefits of clean geothermal energy continue for decades to come.
Because the city's geothermal system is a shared resource, Boise State has a contract designating it as an "interruptible service." That means in the rare case of a service pause, like during maintenance or a repair, campus buildings can temporarily switch to natural gas heating. "If the flow was low for some reason, they could stop giving us service and prioritize buildings downtown," Parrish explained to The Arbiter.
Geothermal energy is one of the most dependable renewable power sources available. It doesn't rely on sunshine or wind to function, and it emits far less pollution than dirty energy sources like oil or gas. That makes it a critical part of the broader shift toward clean, diversified energy — a win for both the climate and public health.
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"I think one of the exciting parts about it, seeing that it's not just a beneficial source of clean energy in Boise, but something where we can set an example for other communities to follow," added Ryan McGoldrick, the program director of Conservation Voters for Idaho, per The Arbiter. "They can come and learn from our experts and help implement a new clean energy source in other places."
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