I'd stick with the 240 volt unit as well. A modern unit with a EER of 10 will consume the same amount of power whether its' 120 or 240 volts though. It will also deliver the same 10K BTUH at either voltage, BTU's are BTU's either way
EER or SEER numbers are ratio's of work performed vs. energy consumed.
If the unit you have / had was 10, 000 BTUH and it consumed a total of 2000 watts of power it would have an E
atio of 5. 10000/2000 = 5.
A more modern unit would have an EER number closer to 9 or 10, so if it's that 10,000 BTUH unit again and it's now only consuming 1000 watts it archives an EER of 10 (10000/1000 = 10).
Double the voltage means half the amperage but = the same in KW's at the meter and out of yer pocket.
But I'd stay with the 240 volt unit as no need to change anything and with this unit drawing half the amperage at start up, there is much less a likelihood of the lights dimming in the house at start up.