The city of Boise says its geothermal heating system is the largest of any city in the country. Now, with climate change looming, Boise is looking to expand the system to new buildings and residential homes.
The city pumps about 250 million gallons of geothermal water — usually 177 degrees Fahrenheit — per year to 96 buildings through 21 miles of high-temperature plastic pipe, mostly located in and around downtown. It accounts for 2% of the city’s energy resources.
This unique system stems from Boise’s unique geography. Underneath a large swath of Idaho lies a batholith, a large igneous rock intrusion. It releases heat, which in turn heats up water that comes into contact with it, typically snow runoff. A large fault line runs through the Boise Foothills, giving the heated water a chance to come to the surface, Boise Geothermal Program Manager Jon Gunnerson said.
That water is then pumped from city-owned wells in the Foothills and piped to buildings on the system and returned, cooler, to the aquifer.
Now, with City Hall having pledged to make Boise carbon neutral by 2050, city leaders are seeking to expand the resource as a clean, pollution-free source of heating in some of Boise’s busiest areas. Geothermal doesn’t create the same emissions found in coal and natural gas.
“Geothermal really provides that clean energy alternative,” Climate Action Manager Steve Hubble said.
The city’s goal is to expand usage of its geothermal system by 5 million gallons per year until it delivers about 355 million gallons, about 40% more than it does now, according to Boise Climate Action Roadmap.
The plan also hints at possible future requirements for new buildings to be heated by geothermal, but Hubble said that plan is still “hypothetical.”
It’s also attractive because supplies remain relatively stable. Under the current model, the city returns a gallon to the aquifer for each one it uses, keeping levels stable and providing a perpetual source of heating.
Boiseans have been using geothermal heat for about 130 years. Residents living in the Warm Springs water district first started using geothermal water to heat their homes in 1892, creating what is now the oldest system of its kind in the country. City Hall began setting up its own geothermal system in the 1980s.
The system is one of at least four geothermal networks in Boise. A private system heats homes on Warm Springs Avenue. The state of Idaho owns a system that serves the Capitol and several state-owned buildings near it. The U.S. Department of Veterans Affairs’ campus has another.
Many of Boise’s most iconic buildings have geothermal heat, including the Capitol, City Hall and the Ada County Courthouse.
“It’s kind of one of those hometown assets that (Boiseans are) really proud of,” Hubble said.
The system also heats 11 buildings on the Boise State University campus, the farthest point on the city’s system. Brian Emtman, Boise State’s energy manager, said not having to add extra heat makes geothermal an attractive resource for such a large institution.
He said the university has hired a consultant to plan how Boise State will use energy in the future, and he expects expanding geothermal to new buildings to be a part of that.
But not everyone will have the option to switch to geothermal. That’s because as water moves away from its heating source, its temperature cools. By the time the water would reach buildings in western parts of Boise, most of its benefit would be lost.
“It’s really going to be the downtown core and within an arm’s reach in each direction,” Gunnerson said.
While there’s a state moratorium on constructing new wells in the area, city spokesperson Colin Hickman said there are no plans for new production wells, as current wells still have plenty of capacity.
While some homes have been connected, Gunnerson said the city anticipates serving mainly commercial clients in the downtown area.
Hubble said for residents living outside the geothermal area, the city is working on providing “clean electricity,” which can come from solar and wind instead of fossil fuels.
Another complication is maintenance the system requires. The system had multiple major leaks in 2018, leading to road closures and expensive repairs. The city settled claims for nearly $450,000 resulting from damage caused by geothermal leaks in 2018, according to the city’s loss run reports.
Gunnerson said some of the pipes are still original and have started to age. The past two years have been spent replacing those pipes, but also addressing any potential problems. As of last summer, the city’s geothermal system is “leak free,” he said.
“The city has to balance the budget that we have for repair and maintenance items against the budget that we have for growth,” Hubble said.
Customers are charged a geothermal rate, which helps fund maintenance for the geothermal program. That rate is competitive to natural gas prices, according to the city. The rate for geothermal is about 85 cents per therm, Hickman said. Intermountain Gas Co., by comparison, charges about 41 cents per therm for its gas, not including fees it adds to monthly bills.
Gunnerson said those interested in switching to geothermal should contact his office for more information.