Given equal room size and same temperature differential, what uses more electricity: A/C or Electric Heater? : Eco Answers

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Question by Jay Horita: Given equal room size and same temperature differential, what uses more electricity: A/C or Electric Heater?
I’ve been hearing conflicting answers to this. Some say an A/C because all it does it moves heat from one place to another, others say a heater because it uses 100% of the energy to do so (whereas energy would be lost as heat in an A/C).

I don’t like the last answer because “efficiency” is looked at in a thermodynamic sense. Yes, 100% of the energy is used to heat up the molecules, but maybe it doesn’t require 100% of the same amount of energy to move heat from the inside to the outside. To change temperature, you have to consider specific heat, whereas moving something just uses the energy required to make the molecules move at a certain velocity.

For example, 1 kilogram of air could be heated up 1 degree with 1000 joules (assuming a specific heat of 1 kJ/kg*K). With 1000 joules though, you could move 1 kilogram of air @ 45m/s.

I could be thinking about this all incorrectly… in which case, I’d appreciate being corrected. Thank you!

Best answer:

Answer by Steve B
All appliances of the same rating (say 1kw) and placed in the center of the room will heat the room by EXACTLY the same amount SO LONG as nothing they generate leaves the room …

Thus a 1kw lamp will have the same heating effect as a 1kw heater or 1kw A/C …

HOWEVER MOST A/C units are mounted on outside walls AND they have vents allowing air to be exchanged between the room and the outside.

In such circumstances an A/C will ‘leak’ heat to the outside (by conduction through the walls and via hot air escaping to the outside) and will thus be less efficient than a heater (especially if the heater is placed away from the walls)

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Given equal room size and same temperature differential, what uses more electricity: A/C or Electric Heater?

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JamesGallo
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