For energy savings on a tight budget, look for the leaks

To comply with Local Law 97 (LL97), One50 West End Avenue had limited options. The Upper West Side co-op was constructed in 1963 with 454 units across 29 stories as part of a larger devel­op­ment meant to serve middle class New Yorkers. But when starting to look at improve­ments several years ago, the building, which now describes itself as an ​“upper-middle-class resi­den­tial haven,” lacked the upfront capital dollars for a full overhaul. 

And perhaps, space was an issue, too: ​“We found out that this building would’ve required more than a foot­ball field of solar panels to meet our rising costs,” said resi­dent Daniel Mori. ​“That wasn’t going to happen here.”

Mori lived at One50 for years before relo­cating to the West Coast. When he moved back to New York in 2022, he returned to the building — this time eager to get involved. So, he joined its board in 2024, which had been weighing a project which fit his back­ground in engi­neering and data. It involved leaks.

Luckily, the water systems were just fine, but an earlier audit had found that the building’s venti­la­tion — the system that removes stale indoor air and brings in fresh air — was eating up about a fifth of One50’s carbon foot­print, nearly twice as much as expected for a prop­erly func­tioning system of that size.

A pre-project assess­ment found One50 was moving far more exhaust air than intended: roughly 150,000 cubic feet of airflow per minute (CFM), compared with a design target of about 78,500 CFM. That’d be like if a garden hose was spraying out water, and suddenly it upgraded to an indus­trial fire hydrant. The differ­ence in flow is massive.

At One50, much of that excess airflow came from leaks in the building’s vertical riser shafts that worked to pull exhaust air out of the building. So, in the summer, when the building’s elec­tric-powered central cooling system ran, the venti­la­tion system pulled this cooled air out of the building; in winter, it was doing the same with air heated by district steam. Each extra CFM of condi­tioned air exhausted from the building cost nearly $2 per year. Pre-project testing found about 71,000 CFM of leakage. In other words: wasted energy — and dollars.

After conducting market research, the board in 2025 approved an opti­miza­tion project with AeroSeal, a company that has for over 20 years sealed duct­work using a sprayable aerosol sealant. The $1 million price tag for the project was nearly halved through subsi­dies from ConEd’s Affordable Multifamily Energy Efficiency Program, in part­ner­ship with NYSERDA. The building covered the rest with a loan.

But the esti­mated annual savings of more than $200,000 in utility bills, which put them on a pathway to comply with future LL97 require­ments, made the pitch appealing. ​“The public-private part­ner­ship allowed us to test this out,” said Mori.

Now, with several months of post-project data, the project has some­thing to show to One50 — and maybe many other build­ings elsewhere.

Riddled with holes

It’s tough to spot air leaks, in large part because they’re invis­ible. Outside of causing a higher energy bill, which could have multiple culprits these days, the signs are subtle. One leak on its own may not be notice­able, but at One50, they added up over time. And for a building this old, outdated envelopes coupled with older insu­la­tion can compound the issue.

All together, they began to have a small but notable impact on everyday life in a building.

Excessive exhaust at One50 created a persis­tent low-pres­sure envi­ron­ment inside the building. That made the lobby doors diffi­cult to open due to the differ­ence between the indoor and outdoor pres­sure. It was common to hear apart­ment doors slam. If a window was open inside, the air was just trying to close the gap. Elevators would hiss. Smells would freely waft between units, and a back­draft that came out of the trash chutes certainly didn’t help. ​“You would always feel a small draft wher­ever you were,” said Mori.

The building staff tried to adjust fans and cover up indi­vidual vents, but to no avail. If anything, it inad­ver­tently made things worse: airflow was now unevenly distrib­uted, leaving some apart­ments with better air quality than others. The under-ventiliza­tion even landed several units with mold and air quality concerns.

When AeroSeal measured apart­ments for airflow, not a single one passed the company’s field testing. The average airflow in a kitchen at One50 was about three to five times the usual airflow, and the bath­room, two to four times. And the building was paying the price: highly inef­fi­cient venti­la­tion meant that in winters, without any inter­ven­tion, the building was set to spend anywhere between $100,000 and $170,000 each month on heating bills. 

“It was costing us a fortune,” said Mori. ​“And for the last three years, it has only been getting worse.”

Plugging it up

On a recent warm and sunny Friday after­noon, Hector, a main­te­nance worker at One50, escorted us to the rooftop. ​“The view is beau­tiful up here,” he remarked. Our focus wasn’t the horizon, but the building’s fans — 24 large metal cylin­ders that dotted the roof. Each one connects down verti­cally to a set of apart­ments through vents and shafts.

The opti­miza­tion work that Aeroseal did sealed the exhaust system from the rooftop curbs, added new airflow controls, and recal­i­brated the rooftop fans. Importantly, it also sealed up the apart­ments them­selves — all 454 units. 

Here’s how the process gener­ally works: First, vents are closed to trap the air inside the duct­work. Then the company hooks up a special machine that pumps air in to test and measure leakage, which is recorded by a computer. Once the gaps are revealed, the aerosol sealant is applied; water-based polymer mist — using chem­i­cals found in most hair sprays — is blown inside, with adhe­sive parti­cles that ​“stick” to the escaping air, sealing up the ducts as it goes.

Each week, the AeroSeal team worked through about two exhaust shafts and several dozen apart­ments. After the leaks were sealed, new vent controls were installed at the kitchen and bath­room exhaust connec­tions, and the rooftop fans were recal­i­brated to run at lower, more effi­cient airflow levels.

In total, the effort took about three months from its start in the summer of 2025, with extra time budgeted for any setbacks. They had to move very method­i­cally: ​“We do these build­ings riser by riser, exhaust shaft by exhaust shaft,” said Christian Weeks, a vice pres­i­dent at AeroSeal. ​“And if there’s one unit on a line that we can’t get into, we can’t do the whole line.”

Thus, commu­ni­ca­tion is essen­tial. At One50, Mori and the other board members acted as primary liaisons between AeroSeal and resi­dents, letting people know when they’d have to offer unit access so the company could get to work sealing gaps. They ended up receiving only a handful of complaints, some from resi­dents with larger main­te­nance issues and others with genuine concern. ​“One person commented about a haze that the aerosol sealing left behind in the hallway for a day or two,” Mori said. ​“But it was nothing we couldn’t handle or respond to.” Board members were able to point resi­dents to AeroSeal’s infor­ma­tion indi­cating that their sealant is non-toxic.

Thankfully, the board had been briefed before­hand. With any project, Weeks said, the company meets with stake­holders — like co-op boards and tenant asso­ci­a­tions — to review both the product and process. ​“We answer all of their ques­tions about our tech­nology, how it works, how we’re going to fix the prob­lems in their building, but also, how we’re going to impact the resi­dents when we mobi­lize to perform the work,” Weeks explained. ​“That upfront engage­ment is critical.” 

It’s airtight

As fate would have it, the new setup faced a formi­dable chal­lenge shortly after instal­la­tion: one of the worst winters in the city’s recent history. Within a few weeks of comple­tion, New York was battered by one of its harshest winters in decades, marked by bliz­zards, polar vortex-driven cold, and subzero wind­chills. This placed a partic­ular strain on heating systems as resi­dents sought to stay warm. At One50, it also made for good data.

AeroSeal’s project team compared One50’s actual heating bills with what the building was expected to spend without the retrofit, using more than two years of past bills and outdoor temper­a­ture data. The test period included major winter weather, including an 11-inch January snow storm and a 19-inch February blizzard. 

From Dec. 22 to Jan. 20, the building’s actual heating bill was $75,000, compared with a predicted $129,000, a savings of 42 percent. From Jan. 21 to Feb. 19, the actual bill was $122,000, compared with a predicted $167,000, a savings of 27 percent. 

Across the first four post-retrofit billing cycles, One50 saved $155,000 on district steam heat.

The 94 percent reduc­tion in leak­ages recorded by AeroSeal contributed to a 75 percent reduc­tion in total exhaust volume — the cubic feet per minute of air mentioned earlier. In other words, the system was now func­tioning far closer to what it was actu­ally designed to do. Now the fans on the rooftop operate at much lower speeds, which reduces elec­tricity costs as well. Anecdotally, Mori reports that many of the previous issues reported by resi­dents have subsided as well.

The pock­et­book savings applied to the foot­print, too: by cutting signif­i­cant amounts of steam, it is esti­mated that 208 tons of CO₂ were avoided in the first four months after instal­la­tion. The building already complied with the initial emis­sions limits in 2025, but this project puts One50 on track to curb steep fines when stricter limits go into effect in 2030.

Now, the AeroSeal team is busy moni­toring the summer season. But based on how a record winter went, they’re expecting a solid return. The impres­sive stats, Weeks said, will be useful in making the case to other build­ings who are looking to afford­ably and strate­gi­cally meet LL97 targets.

“When the board [at One50] looked at the parts of their budget they controlled, it became clear that the energy compo­nent was one of the largest that they could actu­ally do some­thing about. And with utility costs increasing so signif­i­cantly year after year, that was the focus,” said Weeks. ​“That’s a universal issue; I don’t think that’s unique to this building. In New York City and else­where, these rates are a stress, and this can help alle­viate that.”

At One50, the promising imple­men­ta­tion has excited the board about the poten­tial of other cost-cutting endeavors. The team — encour­aged by Mori’s enthu­siasm for a data-driven approach — is exploring ideas like predic­tive analytics, where smart meters and energy modeling can preset venti­la­tion for real-time changes, and digi­tizing asset manage­ment, so the building can prevent main­te­nance issues before they emerge.

“The results here went beyond our expec­ta­tions,” Mori said, while over­looking the Hudson River. ​“We’ll keep moni­toring how it goes. But now we’re wondering: ​‘Where else can we opti­mize? What other wasted energy can we find?’”