Geothermal District Heating in the US: 23 Systems and What the Count Leaves Out

Yes, geothermal district heating exists in the United States, and it is rare and old — though the one national figure in circulation is also narrower than it looks, covering hydrothermal systems only. As of 2021, the National Renewable Energy Laboratory (NREL) counted 23 geothermal district heating systems in the country, most of them more than 30 years old and every one of them in a western state. The oldest has been running in Boise, Idaho, since 1892. The newest of the 23 opened in 2017.

That count has a boundary most write-ups skip. NREL's paper states that the systems it considers "utilize hydrothermal resources as the energy source" and that it "does not consider geo-exchange systems." So the 23 are places piping naturally hot water out of the ground. The shared ambient-temperature loop Eversource switched on in Framingham, Massachusetts, in 2024 — the recent Massachusetts project that gets called by the same name — is a geo-exchange network, and it is not one of the 23. No source here counts systems like Framingham at all.

Three Things Get Called Geothermal District Heating

NREL's count covers only the first of these.

(a) Hydrothermal direct-use district heating — what NREL counts

Naturally hot water from a hydrothermal reservoir, brought up a well and piped to a group of buildings. Boise and Klamath Falls, Oregon, are the American examples; Reykjavik is the famous one abroad. The U.S. Department of Energy (DOE) describes the reservoir under Klamath Falls as ranging from 200–220°F and Boise's water as "naturally heated water at a toasty 177 degrees." NREL's 2021 paper puts the usual serving range at "heating loads between 0.5 to 50 MWth" (megawatts of thermal output).

This is what NREL's 23 systems are. It is also the district-scale version of direct use generally, which our guide to what geothermal energy is used for covers — the same hot water that, at higher temperatures, feeds the turbines described in geothermal power plants. Direct use never generates electricity; it moves heat.

(b) Networked geothermal — a thermal energy network (TEN)

Framingham's configuration: a shared water loop buried at ordinary ground temperature, connecting many buildings, each running its own heat pump against the loop. DOE's description: "Networked geothermal systems offer a community- or district-scale heating and cooling solution, using shared infrastructure among many buildings." DOE frames these as heating and cooling systems, and because "they can balance out buildings with different heating and cooling needs," one building's rejected heat can become another's supply.

DOE's definition is wider than Framingham. A network can be built from "systems using geothermal (ground source) heat pumps, direct use of geothermal heat, or both," and "TENs can draw from a variety of heat sources, including bodies of water, excess heat from buildings in the networked system, wastewater systems, or the stable temperature of the earth." So "TEN" names how buildings are connected, not where the heat comes from — DOE's own list of networked systems includes Boise and Klamath Falls alongside Framingham. What separates Framingham from NREL's 23 is the heat source: NREL counted hydrothermal systems and excluded geo-exchange ones, and Framingham's ambient loop is geo-exchange.

In Framingham, the building-level machine is the same one a homeowner installs, described in our ground-source heat pump guide. What changes is that the ground loop is shared. No hot reservoir is required; the loop sits at whatever temperature the shallow ground is. Eversource's Framingham pilot is the flagship. DOE's page neither restricts where these networks can be built nor gives a ground-temperature range; what it establishes is that they do not need hydrothermal water.

(c) One building's ground-source system

A single house or school with its own loop and its own heat pump. Not a district system at all, though it is often what a search for "geothermal heating" turns up. It appears here only so it can be set aside.

The US Inventory: NREL's 23 Systems, as of 2021

The primary source is Kolker, Beckers, Pauling, Flores, and Robins, "Geothermal District Heating in the United States: 2021 Update," published by NREL in GRC Transactions, Vol. 45 (2021). It presents extracts from the 2021 Geothermal Power Production and District Heating Market Report (Robins et al. 2021). Its abstract: "As of 2021, there are 23 geothermal district heating (GDH) systems in the United States. Most are over 30 years old." The paper is five years old, and every figure below is a 2021 figure.

The paper's Table 1 is titled "U.S. Geothermal District Heating Systems, Net Capacity, and Annual Energy Use (thermal energy dispatched by the GDH system)." Its data note credits the OIT Geo-Heat Center, Snyder et al. (2017), Mattson and Neupane (2017), and 2020 operator interviews. Here is the whole table, transcribed:

Source: Kolker et al., NREL, GRC Transactions Vol. 45, 2021, Table 1. "no data" is carried over from the paper. The paper publishes no totals.

What the table adds up to — our arithmetic, not NREL's

NREL publishes no national total, and two rows are incomplete: Canby/I'SOT and Lakeview Prison have no capacity figure, and Modoc/Alturas and Lakeview Prison have no energy figure. So any sum covers 21 of 23 systems. Summing the rows that report:

• Capacity: the 21 systems with a published figure sum to 89.7 MWth.
• Annual energy: the 21 systems with a published figure sum to 192.3 GWth·h/yr — gigawatt-thermal-hours, heat delivered rather than electricity.
• By state: Idaho 7, California 4, Nevada 4, Oregon 4, South Dakota 2, Colorado 1, New Mexico 1. Seven states, all western — which matches the paper's own sentence that "all of the existing U.S. GDH systems are located in the western states."
• Concentration: Boise City District Heating alone, at 20.6 MWth, is roughly 23% of the 89.7 MWth summed capacity, and its 42.3 GWth·h/yr is the largest energy figure in the table. Idaho's seven systems together account for 37.6 MWth of the sum.
• Age: the paper states that "the majority (15 of 23) of the existing U.S. GDH installations were installed in the 1970s and 1980s," and the table bears that out. Only four rows opened after 2000 — Canby (2003), Lakeview Prison (2005), Lakeview District (2014), and Modoc/Alturas (2017) — all in California or Oregon. The paper names Alturas as "the most recent installation."

The paper also gives one cost figure, and it is a range rather than a number: "Estimated LCOH for existing U.S. GDH systems ranges from $15 to $105/MWhth." LCOH is levelized cost of heat — the all-in cost of delivering a megawatt-hour of thermal energy over the system's life. A seven-fold spread across 23 systems says more about how different these installations are than about what a new one would cost. No capital cost per connected building is published for any of them.

Boise: The 1892 System and the 1983 System

Boise appears twice in the table in two different senses, and keeping them separate matters because one is the oldest system in the country and the other is the largest.

The 1892 entry is the Warm Springs Water District, 3.6 MWth and 8.8 GWth·h/yr in NREL's 2021 table. The paper's own account: "Geothermal energy has been used for district heating in the United States since the Boise, Idaho, GDH system was built in the 1890s. The original district was made up of homes and a natatorium, and the system is still operating today." Homes and an indoor pool, on hot water from the ground, still running 129 years later as of the paper's 2021 writing.

The 1983 entry is Boise City District Heating, the municipal system, at 20.6 MWth and 42.3 GWth·h/yr — the top of the table on both measures. From the paper: "In the 1980s, the City of Boise expanded the GDH system and now holds the record for the largest GDH system in the United States, supplying heat to 92 buildings in downtown Boise (King, 2018)." DOE's page puts the resource temperature at 177°F.

Idaho holds five more rows — the College of Southern Idaho (1980), Idaho Capitol Mall (1982), Fort Boise Veteran's Hospital (1988), Kanaka Rapids Ranch (1989), and Ketchum District Heating (1929) — for seven of the 23, more than any other state in the table.

Networked Geothermal: Framingham and Thermal Energy Networks

Every one of NREL's 23 runs on hot water from the ground. Framingham's network does not, and it is the kind a town without a hot spring would actually be looking at.

Framingham, Massachusetts — what Eversource publishes

What follows comes from Eversource, the utility that built the pilot — its pilot page and reference guide, a vendor's statements about its own project. Eversource calls it "our first-of-its-kind pilot" and says it is "piloting its use at scale in Framingham." Per its pages:

• "On June 4, 2024, we hosted a ribbon-cutting ceremony to mark the commissioning of the pilot."
• "The system is turned on, circulating fluid, and ready to serve approximately 135 residential and commercial customers."
• The shape of the network: "The loop consists of approximately one mile of main pipe and 90 boreholes serving 36 buildings (five commercial and 24 residential for a total of 135 customer accounts)." Elsewhere the same source has "The project route consists of approximately 135 customers: 36 total buildings, 9 housing authority buildings, 5 non-residential and 24 residential buildings." The two breakdowns of the 36 do not reconcile — 5 + 24 = 29 in one, 9 + 5 + 24 = 38 in the other — though both agree on 36 buildings and 135 customer accounts, which are different units.
• On money: "We pay for the cost of building and installing the geothermal system, as well as all the equipment to be installed in homes and businesses." Customers "will pay a low fixed charge each month for access to the geothermal network." The amount: "For residential customers, the rate will be approximately $10 per month, for commercial customers it will be approximately $20 per month, and for our income-eligible customers the rate will be approximately $8 per month."
• On ownership: "The loop system, including the pipes, will be owned and operated by Eversource in perpetuity."
• On performance: "The system has performed well overall, providing consistent heat even on the coldest days. We have had no incidents where the temperature of the loop deviated from our design ranges as of December 2025."
• On federal money: a "$715,000 award" in April 2023 from DOE's Community Geothermal grant program, and "In December 2025, the Department of Energy announced $8.6M in funding awarded to joint partners HEET, the City of Framingham, and Eversource to expand the existing pilot infrastructure in Framingham into the adjacent neighborhood."

The performance statement is Eversource's own; no independent evaluation has been published. Neither Eversource nor DOE publishes an efficiency figure, a customer-savings figure, or a total project cost.

The federal program behind the next ones

DOE's networked-geothermal page reports that "the Office of Geothermal selected 11 community coalitions in 10 states to plan and design community-scale geothermal heating and cooling systems," and that from those, "the Office of Geothermal selected three to install their TENs." The same page notes an earlier federal role in the technology: a Ball State project "funded in part with a $5 million grant under the American Recovery and Reinvestment Act in 2009." DOE's page gives no dollar figure for the 11-coalition program itself.

DOE names the three: "a utility-owned heating and cooling system in Framingham, Massachusetts; a district-scale system to be retrofitted in 1950s buildings in Ann Arbor, Michigan… and a project to support multiple buildings on Tribal lands in Oklahoma." Framingham is therefore both the commissioned pilot and one of the three selections, not a separate project, and the December 2025 $8.6M award extends it.

DOE's page also says there are "many existing or in-progress networked geothermal systems nationwide," and names Boise, Klamath Falls, Ball State University, Barry Farm Redevelopment in Washington, DC, Brown University, Notre Dame, Whisper Valley in Austin, Texas, Seattle Public Schools, Framingham, and New York City. Two of those, Boise and Klamath Falls, are hydrothermal rows in NREL's table — the overlap in one list. What DOE does not publish is a number: no census of operating US thermal energy networks, and no capital cost per connection for any of them.

Iceland: The Contrast Case, Dated 2020

The country everyone reaches for is Iceland, and its number is real: per Orkustofnun, Iceland's National Energy Authority, "about 90% of the energy used for domestic heating in Iceland comes from geothermal energy (2020)." The agency dates its own figure — 2020, not current — and publishes no earlier-year comparison from which a growth rate could be read.

Iceland's heating runs overwhelmingly on the ground's heat and America's barely touches it. Two cautions before leaning on the ratio, though. Iceland's systems are hydrothermal — hot water from the ground, Reykjavik being the well-known example — so Iceland says nothing about how a Framingham-style network would perform. And the American figure usually set against it is a different measurement: NREL's paper states that "direct-use geothermal only provides 0.1% of the current total U.S. thermal demand (McCabe et al. 2019)," which is all direct use against all thermal demand, not domestic heating alone. The two shares point the same direction; they are not the same ratio. Our Iceland geothermal energy guide separates Iceland's heating, electricity, and primary-energy figures, which get merged as often as the two populations on this page.

Why the United States Has So Few

NREL's abstract names the constraints, and geography is only one of them. In the abstract's words, "the market for GDH in the United States has been weak over the past 40 years due to the combination of inexpensive fossil fuel alternatives (mostly natural gas), lack of incentives focused on heating/cooling, and other factors". Geography sets a separate limit: a hydrothermal system needs water hot enough to heat buildings directly, close enough to the surface to reach with a well. The paper reports that all 23 systems are in western states, and the table's seven are Idaho, California, Nevada, Oregon, South Dakota, Colorado, and New Mexico. The same paper discusses resources in many parts of the country, including deeper development in lower-gradient eastern regions, so the western map records where systems were built, not the only places one could be.

Neither NREL nor DOE gives a temperature threshold below which a reservoir is too cool for direct-use district heating. The two figures DOE does give — 200–220°F under Klamath Falls and 177°F at Boise — describe two specific reservoirs, not a minimum requirement.

Fifteen of the 23 were built in the 1970s and 1980s; four opened after 2000; and "most are over 30 years old" as of 2021. The paper's most recent installation, Alturas in 2017, is a 0.44 MWth school system. The record is of a technology built out where the resource was easiest to reach, mostly within two decades, with small additions since — against, in NREL's account, cheap natural gas and no heating-focused incentive to push it further. And the cumulative result, per the McCabe et al. figure NREL cites, is 0.1% of US thermal demand.

What Would Have to Be True for Your Town

It depends on where the heat would come from.

For conventional direct-use heating: is there hot water underneath you?

A hot-water system needs a reservoir within reach, and every one of NREL's 23 sits on one. NREL discusses deeper development in lower-gradient eastern regions, but none of its 23 systems is there. The 23 systems in the table serve loads from 0.1 MWth (Midland, South Dakota) to 20.6 MWth (Boise), and the paper's general range for the technology is 0.5 to 50 MWth. NREL's one cost figure, the $15 to $105 per MWhth levelized range for existing systems, is too wide to plan a budget on. What finding and tapping a hot resource involves is covered in our guide to geothermal drilling and wells.

For a networked system: what is and is not known

A thermal energy network does not need the hot reservoir, which is why it is the version being piloted in Massachusetts rather than Idaho. What is established: one utility pilot, commissioned in June 2024, serving approximately 135 customer accounts in 36 buildings. The utility paid for the network and the in-building equipment, owns the loop in perpetuity, and charges approximately $10 a month to residential customers, $20 to commercial, and $8 to income-eligible customers. Eversource reports the system has performed well through December 2025. DOE has selected 11 coalitions in 10 states to plan and design such systems and three, Framingham among them, to build, and in December 2025 it awarded $8.6M to expand Framingham into the adjacent neighborhood.

What NREL, DOE and Eversource do not establish: how many such networks operate in the US, what one costs per connected building, or how Framingham performs by any independent measure. A town weighing this today is weighing a technology with a published concept, a published rate, and a vendor-reported operating record.

If the physics is new to you, start with what geothermal energy is — the difference between hot water from a reservoir and the stable temperature of shallow ground is the one NREL's scope statement draws.

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