Best height for thru wall AC unit?

I'm about to install a 14500 BTU AC unit as a thru wall and have to physcial or electrical restrictions on how high to install it so was wondering what would be the best place. The room is 20'x21' and it will go midway down the longer side, about 1/3 of which has a suspended floor the rest is open cathederal ceiling. AC can go anywhere from the main floor to just below the suspended floor height.
As a side question does anyone know how to compare for example if a 9 seer unit at $100 is a better deal or not than a 10 seer at $130? Is it linear, ie a 10 seer uses half the electricity of a 5 seer?
Thanks
Nick..
BTW. Home Depot has 30% off all AC units right now.
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Its not linear but depending on kwh cost it could pay for the 30+ in a month.
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according to an energy star a/c chart I have, 14500 btu eer 11.1 (friedrich rs10j10) is 14% better than a 9.7 (federal standard eer).
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Since hot air rises, as high as possible should theoretically be better. However, if over shoulder height, it may make periodical maintenance and removal for service more difficult and sounds from it might seam louder if installed at head level (either standing or seated).
JMO
Dan O. - Appliance411.com http://ng.Appliance411.com/?ref411=air+conditioner
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