Box fans are cheap to run 24/7

Running a box fan 24/7 will increase your electricity bill, but not by much — usually under $10 a month.

Most box fans draw around 50–100 watts on high. Let’s say 75W average. Run it 24 hours a day for 30 days, that’s 54 kWh. At the US average of $0.14/kWh, you’re looking at about $7.50. Even if your fan is an inefficient hog at 120W and your rate is higher, you’re still under $15.

Compare that to a central AC or even a window unit, which can pull 1,000–1,500W. A box fan is practically nothing. If it keeps you from cranking the AC, it’s actually saving you money.

One thing: fans cool people, not rooms. If you leave it running in an empty room, you’re just moving hot air around. That’s still cheap, but also pointless.

Final thought: Don’t worry about the fan. Worry about the AC.