By Jackie Snow

It took seven years, but Jocelyn Hittle finally got what she wanted: a heating and cooling system fueled by wastewater at Colorado State University's new Spur campus in Denver.

When Hittle finally moved into one of the buildings served by this system, the most surprising thing was how utterly unremarkable it felt.

No unusual odors. No strange noises. Just the same comfortable indoor climate she'd experienced in conventional buildings throughout her career.

"As an occupant of the building, everything feels exactly the same," says Hittle, associate vice president at CSU for special projects and the Spur campus, a three-building complex at the National Western Center in Denver. "The only difference is that we get to tell that story and have our visitors understand that we're doing something new and how it helps us to meet our energy and climate goals," she says.

According to Energy Department estimates, Americans flush the equivalent of 350 billion kilowatt-hours of energy from hot water down their drains annually. A substantial portion of this thermal energy is recoverable, yet most municipalities and building managers have barely begun to tap this resource.

Wastewater heat-recovery systems, which have been widely adopted in Europe, are gaining momentum in North America as the technology becomes more accessible and cost-effective. Major projects in Denver; Vancouver, British Columbia; New York state; and King County, Wash., are either expanding existing systems or breaking new ground.

And dozens of smaller installations in individual buildings are happening around the country.

Several benefits

The technology is relatively straightforward. The temperature of wastewater is typically between 54 and 67 degrees Fahrenheit, making it a source of thermal energy. Heat-pump systems can recover that energy and use it to help warm buildings and heat water, and to cool buildings in warm weather. That helps cut carbon emissions and boost energy efficiency by replacing fossil fuels.

"Sewage is warm because we take hot showers and wash our hands with warm water, run the dishwasher -- all of that thermal energy is literally just flowing down our drain and into the sewer system," says Derek Pope, who oversees a wastewater heat-recovery system in Vancouver.

In the National Western Center's system in Denver, the cooled wastewater flows into the city's sewer system. That reduces the amount of water, time and energy that sewage treatment plants need to cool wastewater, which they do to avoid ecological damage when the treated water is released into waterways.

"The system saves the equivalent of six million passenger vehicles of emissions and five Olympic pools worth of water a year," says Brad Buchanan, former planning director for the city of Denver, who now heads the National Western Center Authority.

Vancouver was an early adopter of this approach in North America. The city's False Creek Neighbourhood Energy Utility began operating the first sewage heat-recovery system on the continent in 2010.

The system started with providing heat to nine buildings in the 2010 Winter Olympic Village and has grown to serve 47 buildings housing about 10,000 residents, along with a community center, science center, university and various office and retail spaces.

The utility now delivers 70% of its energy to customers using renewable energy, with wastewater heat recovery being the "primary" piece of it, Pope says. That has reduced carbon emissions by around 7,000 tons a year compared with natural gas, according to Pope.

Gaining traction

Despite its efficiency and proven record, wastewater heat recovery remains relatively uncommon in the U.S., while European cities have widely implemented these systems. The difference comes down to infrastructure. Countries like Sweden and Denmark developed extensive district heating networks decades ago, making it easier to integrate wastewater heat recovery. These centralized systems already have the pipes in place to circulate recovered heat throughout neighborhoods.

"In Sweden, any area that is densely populated is served with district heating," says Semida Silveira, professor of energy systems planning at Cornell University. "District heating is a very efficient way of heating homes."

In contrast, most U.S. buildings rely on individual heating systems, which can still recover heat but require new infrastructure for each building. That works, but not as efficiently as centralized solutions, according to Silveira.

However, these projects on a smaller scale are gaining traction, thanks to new systems sized specifically for multifamily properties. In New York state, construction of a wastewater heat-recovery system has begun at Whitney Young Manor, a multifamily housing development in Westchester County, and a system is being designed for the Amalgamated Housing Cooperative in the Bronx, both with support from Nyserda, the New York State Energy Research and Development Authority.

Nyserda is receiving inquiries from other building owners interested in the possibility of replicating the approach, says Michael Reed, the agency's acting head of large buildings. But they need some questions answered before diving in.

"When there's a new product, people are interested, but they're also skeptical," Reed says. "They need their preferred engineering consultant to really dig into the tech and come back to them and say, 'Yes, this makes sense, and it can work.' "

Jackie Snow is a writer in Los Angeles. She can be reached at reports@wsj.com.

(END) Dow Jones Newswires

April 19, 2025 10:00 ET (14:00 GMT)

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