My first summer electric bill was $340. I lived in a 900-square-foot apartment. I called the power company thinking there had been a meter error. There was not — I had just been running the AC at 68 degrees around the clock with zero strategy.

The next summer, I kept the apartment comfortable and cut the bill by 40%. Here is what I changed.

Raise the Thermostat When You Are Not Home

This is the single biggest lever. If you set the AC to 78 or even 80 while you are at work, and drop it to 74 when you get home, you save significantly. An AC unit works harder to maintain a temperature difference than to create it. Letting the house warm up during the day — when nobody is there — and cooling it down in the evening uses less total energy.

Get a Programmable or Smart Thermostat

A basic programmable thermostat costs $25 and lets you set a schedule: 78 during work hours, 76 in the evening, 74 at night. A smart thermostat like a Nest or EcoBee learns your patterns and adjusts automatically. The smart versions cost more upfront but pay for themselves in about two years through energy savings.

Clean or Replace the Filter

A clogged AC filter restricts airflow and makes the unit work harder. Change or clean it every one to three months during cooling season. A $5 filter can save you $20+ per month in electricity. I mark my calendar for the first of every month during summer — it takes two minutes.

Use Ceiling Fans

A ceiling fan makes a room feel 4 degrees cooler without actually lowering the temperature. It cools people, not the room — so turn it off when you leave. Running a ceiling fan costs about $0.01 per hour. Running an AC costs 50 to 100 times that.