Energy Usage, Conservation and Weather Stripping - 110v vs. 220v heat and A/C- Which costs more to run?

My buddy and I were talking about window A/C units and we came up with a question neither one of us could awnser. If I run a 110v A/C unit (or heater for that matter) does it cost more than a 220v unit? I understand 220v is probably more effecient overall, but I am more so wondering how the power company charges....

Another way to look at it would be 2 light bulbs. Does it cost more, less or the same amount if both bulbs runs on the same 110v leg instead of balancing the load between both 110v legs in the house? Do you see what I am asking? If most of the power is being used from one leg vs. both legs evenly.....Beer 4U2

Excellent question, I would like to know the answer also. You should post this in the electical forum, the experts there will have an answer.

As far as the light bulb it does not matter what leg they are connected to, there is no change in wattage even with different amounts of bulbs on each leg. Hope that makes sense.

So you think it is most likely total watts, no matter which leg. That makes the most sense to me (and probably the power company as well).

Milemaker is right in that you pay for power in watts.
Watts of consumption has nothing to do with the voltage.

If you have a 1000 watt heater it would in rough numbers draw 8.3 amps at 120 volts.
A 1000 watt heater at 240 volts would draw 4.15 amps.
Wattage equals volts times amps and is the same no matter what the voltage.

Having said this it is sometimes better to operate devices on 240 volts for the fact that you can carry the same wattage on smaller wire because the amperage is half on 240 volts.