Is it much more cost effective to use 220v on a portable air conditioner for a small room vs using 110v:confused:

Assuming the same BTU rating between a 240 volt and a 120 volt AC unit, there will be no or negligible difference in energy costs.

Using 240 volts over 120 volts, for any device that draws the same power, does not help save power.

I believe you need to refer to the Energy Star SEER rating to find the lowest rating to compare units for energy costs.

I will copy this over at HVAC forum, to see if any of the HVAC experts can help with choosing a unit.

No. Just make sure the circuit can handle whatever you're plugging in.