A woman cools off in the fountain at Washington Square Park Thursday in New York City. Getty Images

If you're in the Big Apple, you might need to adjust your weekend schedule, because it's getting hot in herre.

The National Weather Service issued an excessive heat warning Friday for New York City and the southern part of the state through 10 p.m. EDT Sunday. The service warned that heat index values — or how hot it feels outside — could reach 110 degrees on Saturday.

CBS reported that at a news conference, Mayor Bill de Blasio warned the city, telling New Yorkers not to be outdoors this weekend unless they must be. Then he added a catch: He requested you chill out on your A/C usage.

"The last thing any of us wants to go through is a blackout," de Blasio said. "If you set your air conditioner to 78 degrees, you’ll be fine, and you’ll help protect yourself and everybody else from the danger or a power outage."

Now, 78 degrees may sound nowhere near the temperature you want your home to be in what the weather service is calling "oppressive heat and humidity." But it might not actually be such a crazy idea.

As noted in "The Building Environment: Active and Passive Control Systems" by Vaughn Bradshaw, the American Society of Heating and Air Conditioning Engineers' comfort standards states that "the preferred temperature range" for people wearing summer clothes is 73 to 79 degrees Fahrenheit.

This is especially true if you're trying to save money on utilities: The U.S. Department of Energy explains that cranking the thermostat to be colder than normal "will not cool your home any faster and could result in excessive cooling and unnecessary expense."

However, Consumer Reports notes that cooling rooms with window units, which are everywhere in New York City, may be a little harder. It recommends turning on the A/C to 78 degrees, waiting a while and adjusting accordingly.

Still hot? Don't forget you can keep yourself cool in other ways, like closing your blinds, drinking lots of water and using fans.

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