Dick wrote:
I have 2 window units:

1. an 18,000btu 220V
2. a 10,000btu 110V

I remember reading somewhere that, while obviously bigger & more
powerful, the 18K unit is cheaper to run because it's 220V.
This is counter-intuitive but does anyone know?

A question that sounds easy, but is complex.

Let's start with your question about using less power. If you mean how
much total electrical power (and cost) it uses per minute while it is in
cooling mode, you will need to check the number of amps and multiply the
220V (likely 240V) times to and then compare them.

Of course this does not really help since one will be producing more
cooling than the other. Generally the larger units are more efficient using
less total electricity to produce the same amount of benefit and thereby
often run less long so over a 24 hour period they may use less total
electricity.

While it is often true that a 240V unit will be more efficient than a
120V unit it is not always the case. New units should carry a SER number,
higher is better. The SER number tells you how efficient a unit is at in
test situations and fairly compares units using different voltages.

Finally it is not all about cooling. Humidity control is also
important. Have a unit that is too large can short cycle and not be able to
remove enough moisture from the air to be comfortable.
--
Joseph Meehan

Dia duit