As New Yorkers sweat through relentless heat this summer, many are cranking up electric fans in a desperate bid for relief.

But a shocking new study throws cold water on the popular cooling fix, warning it could actually backfire for older adults under certain conditions.

Studies have indicated that in intensely hot environments, the use of a fan can actually raise the body temperature of elderly individuals, potentially increasing their susceptibility to heat exhaustion and other hazardous health conditions.

The study, conducted by scientists in Australia and Canada, tested how electric fans affect older adults under both dry and humid heat conditions.

In the initial study phase, 31 participants, all aged 60 and above, were exposed to harsh, dry heat conditions—specifically, temperatures of 100.4°F with a low humidity of 15%—to mimic extreme indoor heatwave scenarios.

During the study, each participant underwent four distinct three-hour trials, each spaced at least 72 hours apart. These included using a fan only, wetting the skin without a fan, wetting the skin with a fan, and employing no cooling method at all.

Instead of cooling them down, fan use in dry heat caused participants’ core body temperatures to rise by 0.5°F. They also reported feeling hotter and less comfortable.

The findings suggest that, rather than cooling the body, the fan was actually pushing heat into it.

Previous research from the same team found that fans used in hot, dry conditions tripled cardiac strain in older adults — a potentially deadly consequence for people with heart disease.

“In very hot and dry heat, fan use worsened all outcomes and should be discouraged for these conditions,” the study authors wrote.

The second phase of the study focused on hot, humid conditions. This time, the researchers included 58 older adults — including 27 with a history of coronary artery disease, who had been excluded from the dry heat tests due to potential heart risks.

In these tests, room temperatures again reached 100.4°F, but with 60% humidity.

Unlike in dry heat, fan use in humid conditions slightly lowered participants’ core temperatures by an average of 0.18°F. It also boosted sweating and made participants feel cooler and more comfortable overall.

An earlier study by the same team showed that fans — with or without skin wetting — also helped reduce cardiac strain under similar humid conditions.

Together, researchers say the findings challenge CDC guidelines that advise against using fans when temperatures exceed 90°F, citing a potential increase in body temperature and related health risks.

“While air conditioning is an effective way of staying cool, it’s not available to everyone, especially those most vulnerable to the heat such as the elderly and people with heart disease — so it’s positive news that low-cost alternatives are effective, Dr. Daniel Gagnon, a researcher at the Montreal Heart Institute and co-author of both studies, said last year.

“Importantly, the study has shown that the weather conditions affect the type of cooling strategy that should be used — a vital piece of information that will help older people to stay safe in heatwaves,” he added.

Heat waves are becoming more frequent across major US cities — and more dangerous, as sweltering overnight temperatures offer little relief from the day’s heat.

Each year, an estimated 60,000 Americans end up in the emergency room due to heat-related illnesses like heat exhaustion and heat stroke — and more than 13% of those cases require hospitalization, according American Medical Association.

In New York City, the danger is already playing out. On June 25, a record-breaking 99°F scorcher sent 141 people to emergency rooms with heat-related issues — the highest single-day total since 2017.

Extreme heat is the deadliest weather-related hazard in the US, with more than 14,000 deaths directly linked to heat since 1979. But experts warn the true toll may be far higher, as heat is often underreported or overlooked as a contributing factor.

In New York alone, more than 500 people die prematurely each summer due to extreme heat — the vast majority inside their homes without air conditioning.

The city operates cooling centers to help vulnerable residents, but for those relying on electric fans at home, the new research makes one thing clear: check the humidity.

If it’s dry, that fan could leave you even hotter than before.