ON A WEEKDAY MORNING in Boston’s Longwood Medical Area, patients hurry between hospital buildings for appointments. Parents push strollers toward Boston Children’s Hospital. Doctors and nurses rush as ambulances arrive outside the emergency department. At other nearby hospitals, just blocks away, the everyday whir of activity continues: Babies are born, broken bones are mended, and patients with respiratory problems, who are especially vulnerable to the effects of pollution, shuttle to their doctors.

Within sight of Boston Children’s Hospital — and many of the other medical facilities — another structure rises above the neighborhood, smoke billowing from its massive chimney. The Medical Area Total Energy Plant (MATEP) supplies electricity, steam, and chilled water to Children’s and many of the hospitals and research institutions in Longwood where doctors care for thousands of patients each day.

The plant rarely appears in conversations about public health, but it’s a key reason why many hospitals in Boston — powered in part by the fossil-fuel-driven MATEP — are also among the city’s largest sources of greenhouse-gas emissions, contributing significantly to the pollution that is closely linked with asthma, cardiovascular disease, kidney disease, and even dementia.

Regina LaRocque, an associate professor of medicine at Harvard Medical School who researches the effect of climate change on human health, said the implications of fossil fuel use are not in question.

“As doctors and health professionals, our primary responsibility is to do no harm,” she said. “But what often gets overlooked is that the operations of our institutions can actually cause harm. Hospitals and health care systems have a footprint. That includes pollution and climate impacts.”

About 70 percent of Boston’s greenhouse gas emissions come from buildings, according to city data.

“If the city wants to make real progress on climate goals, the building sector is where the biggest changes have to happen,” said ​​Hessann Farooqi, executive director of the Boston Climate Action Network, a community-based organization that works with Boston residents to advocate for climate justice and stronger clean energy policies.

That’s the goal behind Boston’s Building Emissions Reduction and Disclosure Ordinance (BERDO). The policy, which was enacted more than a decade ago, requires large buildings to report their energy use and gradually cut emissions to reach net zero by 2050 — a task that remains especially complex for hospitals. Hospitals are required to reduce emissions under BERDO, but they have limited control over the energy system.

“There’s only so much they can do; they can’t force MATEP to do things differently,” said Mireille Bejjani, co-executive director of Slingshot, which organizes communities facing environmental pollution.

Building owners are “just starting to understand how their buildings perform,” said Aidan Callan, Boston’s BERDO program manager, adding that reporting data is the first step toward reducing emissions. Already, there’s one clear takeaway: Hospitals stand out as some of the lowest-performing buildings in the city, according to CommonWealth Beacon’s analysis.

BERDO tracks compliance with emissions goals by analyzing a building’s size, energy consumed, and the types of fuel used. It also includes an Energy Star rating, which compares a building’s performance to similar buildings across the US, though it doesn’t always capture emissions intensity.

It’s similar to the rating on most home appliances, but takes into account factors such as a building’s size, type, occupancy, and energy use compared to similar buildings. Four out of five buildings in Boston fall into just two categories: multifamily housing and office buildings. These tend to perform relatively well in the city’s energy data, with both having an average Energy Star score of about 71.

The ratings for hospitals are a different story.

To better understand what drives these low scores, CommonWealth Beacon reached out to hospitals across the city, including Beth Israel Deaconess Medical Center, Massachusetts Eye and Ear, and Brigham and Women’s Faulkner Hospital. Most declined to comment or did not respond, but Smith from Boston Children’s Hospital explained MATEP’s role in its energy use and emissions. (Officials with MATEP and its parent company, ENGIE North America, did not return emails seeking comment.)

Because the plant operates as a private utility and is not subject to the same regulations as the traditional grid, “the emissions can be higher associated with the plant and the utilities,” Smith said, calling it one of the hospital’s “most unique challenges.”

But the structure of the energy system is only part of the story. Hospitals themselves have far more demanding energy needs.

“Hospitals are energy-intensive buildings because they’re running 24/7,” said Farooqi. “They have a lot of specialized equipment. So any hospital is going to be a high power user.”

At Boston Children’s Hospital, Smith points to ventilation as one of the biggest drivers of energy use. In clinical spaces, he said, systems may require “20 to 40 air changes an hour at 50 or 60 degrees, when it’s 100 degrees outside,” which means hospital systems are constantly pulling in outside air, cooling it, filtering it, and replacing the air inside, sometimes every few minutes, to prevent the spread of infection.

That level of demand can increase dramatically during periods of extreme weather, when energy use spikes across the system. Peaker plants run on the hottest and coldest days, to meet the rising energy needs as people need to cool and heat their homes — days when people are already more vulnerable because of the temperature swings.

Those requirements help protect patients, but they also push hospital energy use far beyond most other building types.

A similar tension is visible from inside the hospitals themselves.

“It’s a very fascinating trade-off,” said Maddy Kline, an MD-PhD student at Harvard Medical School. “You have to be able to provide patients with the best possible care … but at the same time, it’s mind-boggling that the air inside the hospital has to be so clean, and then you step outside and you’re right next to these fossil fuel burning power plants.”

MATEP operates on a co-generation model, producing electricity and heat from the same fuel source. Two natural gas turbines and six diesel engines generate power on site. Instead of venting hot exhaust as waste, the facility captures that heat to produce steam for nearby hospitals and research buildings, allowing the system to extract more energy from each unit of fuel than a conventional power plant.

MATEP was built in 1974 with one priority in mind: keeping the lights on. Each year, the plant releases roughly 290,000 tons of carbon dioxide, nearly 600 tons of nitrogen oxides, and significant amounts of particulate pollution. Today, the environmental cost of that model is being thrown into sharp relief.