Air Conditioning - Not the usual A/C size question...

...because I know the minimum size I need.

I'm in the market for a new window A/C. I've already calculated that I need 10-12.5K BTU (probably closer to the 12.5 given southern exposure and # of windows) for what I'm looking for. However, in shopping around, I've found an 18K BTU for about the same price as at the 12k BTU.

My question is, since they have the same EFF rating would I end up saving more money in the long run by buying the larger one, because in theory, since it's more "powerfull" the compressor would not have to run as long to cool the same area as the smaller one.

Thanks for any insight you can give. Is there a formula for figuring this out so I can find the tipping point where one would be more cost-effective in the long run or is it just a common sense thing?

Thanks,

Matt

Is this for just a window unit are like a whole house unit?
If window just go for the bigger unit to drop the temp faster. if like for a home go smaller so the unit has to work and run that way it gets the humidity out of the home and you will be cooler at a higher temp.


ED ;)

...a window unit and whole house unit. It will be used to cool most of the 1st floor (approx 500-600 sq ft), but primarily a large living room (360 sq ft) connected by large arch to a seldom used dining room and kitchen.

-Matt

What electrical outlet do you have available?? The 18,000 will more than likely need 220. The 12,000 you can use 120.

...I only have a standard outlet on that side of the room, so it looks like my question is now mute. Either way, it'll be a lot better than the heinously loud monster it will be replacing.

Thanks,

-Matt