New Delhi, Nov. 19 -- Every winter the same question comes back. Do you really need a separate room heater when you already have an AC on the wall. In cities across North India, families move from one plug point to another with blowers, rods and oil filled radiators, while the split AC just sits there, waiting for April.

Hot and cold ACs promise to change that and turn one machine into your year round comfort setup. But can they actually handle a sharp north Indian winter night on their own.

In this story we look at that question in a clear, real world way. We break down how hot and cold ACs heat a room, what changes when the temperature outside drops, and how much of a difference insulation and room size make. Along the way we have pic...