The final day for landlords to keep the air conditioning on in Massachusetts is Sunday, Sept. 15. That means for many apartments without window units, landlords will switch over from air conditioning to heat for the cold winter months.

The change isn't based on yearly temperatures. Instead, it changes based on a set day.

"If you're living in a large building or even a semi-large building with an HVAC system, it's not always easy to switch between cooling and heat," Ethan Masscoop, a clinical instructor in environmental health at Boston University, told GBH.

The local boards of health can decide to change the date of heating season, instead starting on Sept. 30. Temperatures also should not exceed 78 degrees, the state clarified.

Air conditioning will then turn back on starting May 31.

"That means officially we have three months of spring, summer, and fall in Massachusetts," Mass Landlords, a non-profit for owners and managers of Massachusetts residential real estate, states on its website. "The rest is legally considered the dead of winter!"

Prior to April 2023, heating season lasted until June 15, meaning landlords couldn't turn on air conditioning until then.

Mass Landlords said they worked to change the date "in response to climate change."

Representative Bud Williams told Western Mass. News he hopes one day every tenant will have their own A/C unit.

"I understand the frustration," Williams told the news outlet. "When you're in those apartments and it gets to 90 and you're there, doesn't matter if it's for one day or two days and you have to live through it and bear through, it's almost unbearable."