Boise began drilling for geothermal water in the late 1890s; four systems now heat an estimated 7.4 million square feet, including much of downtown

Your winter heating bill probably makes you wince a little. In the city of Boise, Idaho, though, a large section of downtown is warmed with water that has been heated in the ground already, and has been that way, in various forms, since the 1890s. According to a 2017 paper, "The Nation's Oldest and Largest Geothermal District Heating System," by Leland Mink, published in the journal GRC Transactions, drilling for hot water there began in the late 1890s. Boise now has four geothermal heating systems, which together heat an estimated 7.4 million square feet. The figures Mink cited are as of 2017, so take them with a grain of salt. The details behind the numbers are more interesting.

A 19th-century system with real staying power

The city's early geothermal push moved quickly. According to Mink, crews hit 175-degree water 404 feet underground in January of 1891. Homes on the system were paying "$2 to $3 dollars a month," while other residents in Boise were paying $7 to $8 a ton for coal. A huge indoor swimming pool, the Natatorium, opened in the city in 1892, and its pool was among the largest in the country.

The system did not stay fashionable, as a windstorm destroyed the Natatorium in 1934. Rotting wooden pipes, cheap hydropower, and the advent of natural gas in 1956 shrank the network to about 200 homes and a handful of businesses by 1970. Rising gas prices and a new interest in renewables in the 1970s pulled it from the brink, and it's still running today as the Boise Warm Springs Water District, serving several hundred homes in the city's East End. That 1970s comeback is a separate thread from the story of downtown's newer, larger city-run system, which came later: Boise didn't add its city-owned downtown geothermal system until 1983, and the state capitol and VA hospital systems were built out in the 1980s as well. So the old East End network was never a visionary master plan; just a story of what was cheapest at the time, one that happened to survive.

Free heat, but with limits

Even a hot spring can be abused. As per Mink’s accounts, Boise's geothermal aquifer dropped nearly 50 feet between 1981 and 1989. A 1999 injection well fixed much of the problem by returning the used water underground, and the aquifer climbed back up close to its pre-development level. That decline and recovery is specifically about the shallow, naturally occurring hot-water aquifer that all four of Boise's systems draw from: a local, finite resource that has to be actively monitored and topped up. The lesson for proponents of "unlimited" clean energy is that a resource like this can be renewable, and still require careful management.

According to Yale Environment 360's 2020 coverage by Jim Robinson, the city's downtown system alone, one of the four, and the largest of them, heats about a third of downtown, or about 6 million square feet, across roughly 90 buildings. The remaining 1.4 million square feet in the 7.4-million total comes from the other three systems: the Idaho State Capitol Mall complex (about 800,000 square feet), the VA Medical Center (about 500,000 square feet), and the older Warm Springs Water District network (roughly 500,000 to 1 million square feet across several hundred homes and businesses). Robinson reports that the electricity to pump the water comes to around $1,000 a month. That's only pumping, though. The same article puts the yearly cost of depreciation, maintenance, staff, and repairs at about $750,000, which is still a small number for that many square feet of heating.

But why aren't we all just doing that?

Blame the geology and the money. According to Robinson at Yale E360, few places have naturally hot water underground, so this kind of heating system has been a local curiosity. The article also covers that the deep geothermal resource has lagged mainly due to high start-up costs. Cornell professor Jefferson Tester, quoted there, said, “ Wherever we are on the surface of the planet, and certainly the continental U.S., if we drill deep enough we can get to high enough temperatures that would work like the Boise system. It’s not a question of whether it’s there; it is there, and it’s significant. It’s a question of getting it out of the ground economically.” Tester is talking about deep heat in the Earth's crust generally, which is essentially everywhere if you drill far enough down, a different resource from Boise's shallow, naturally recharging aquifer, which is what actually needs the careful management described above. Boise had a head start because nature happened to put hot water close to the surface right where the city sits, at a depth that was cheap to reach even in the 1890s.

Multifamily housing, still waiting

Here's the crucial insight. According to the city of Boise's announcement in February 2026, the network is serving about 100 downtown buildings. The city also says regulatory and billing issues have made it difficult for multifamily housing to connect. A $1 million award from Bloomberg's Mayors Challenge is meant to help them do so. The city talks of a planned affordable housing pilot in the Lusk District, expected to be finished in 2028, with potential utility savings of up to 80%. Those are the city's projections, not results. Yet it's telling that renters could be among the last to get plugged into a system which began more than a century ago.

You can't copy-paste Boise into someplace else. It's a demonstration of how municipal-scale heating can be powered via geothermal, with the limits that entails: geology, start-up costs, and who actually gets connected. As other cities weigh cleaner heating options, the open question isn't whether geothermal district heating works, Boise has shown that it does for well over a century, but who gets access to it first.