Should windows be open while the AC is running? Does an AC need ventilation?

Keep windows closed while the AC is actively cooling — open windows let conditioned air escape and outdoor heat in, making the unit work harder and less efficiently for no benefit. Periodic fresh air when the AC is off (between sessions, or briefly each day) is a reasonable general practice for any sealed room, AC or not.

📐 Calculated estimate Based on real BEE-certified data — see the exact numbers below.

This is really just basic thermodynamics, not an AC-specific rule — any time conditioned air can freely exchange with outdoor air, the system has to work harder to compensate, which shows up directly as a higher electricity bill for the same comfort level. It's not that the AC "needs" ventilation to function safely; it's that keeping the room sealed while it's running is simply how the unit was designed to work efficiently.