There is a drawback to these, compared to a window unit or a split system as someone mentioned above- In both a window unit and a split system, you are basically using a closed system, similar to when you set the A/C in your car to recycle using inside air rather than drawing in fresh air from outside. Since A/C systems, depending on their cooling capacity, have the ability to lower the temperature of the air passing through by Xnumber of degrees, the temperature of the air being pulled into it for cooling purposes is key to efficiency and associated costs. As an example- if your A/C unit will cause an 18 degree cooling differential, how long and hard it runs is greatly impacted by your source of "return" air and it's temperature. For a window or split unit, you're continously cooling the same air, so in a 400 sq foot garage shop as you keep pushing the same roughly 3200 cubic feet of air through, as the temp lowers in the room overall the output of the a/c unit will keep lowering by that 18 degree cooling differential, until it turns off if you have it set with a thermostat. On the unit that has to be vented to the outside, you're pushing the heated air out which can cause negative pressure if you're in a fairly snugly constructed building. There neeeds to be a source for replacement air, so if you do provide fresh air from outside, you lose a lot of the benefit of continously chilling the same air in a closed system. So say for example, your return air is coming from a secondary vent pulling in outside air, and like me you're here in Texas (and yes, I did have one of these systems, and a pretty nice one, before converting to a large cooling/heating window unit). July comes along and at 3:00 in the afternoon it's 98 - 100 degrees outside. Maybe 103. Definetly 103 if it's August. If that's my source for replacement air, I'm fighting a loosing battle if I'm trying to cool the whole Garage. At least I'm loosing if I'm trying to get it down into the 70's (which is the temp I find turning at most pleasant). If I set the thermostat to 75, and the replacement air is coming in at 98, and my cooling differential is 18 degrees, I can count on a pretty hefty electric bill 'cuz that puppy is not ever going to quit running. Granted, if you fire it up first thing in the morning when it's cooled off to about 80 here (July/August), you can get ahead of the curve for a decent part of the day, but you still maybe looking at running that puppy all day long. The two years I tried running mine I gave up on trying to cool the entire shop. I was able to patch in an extension hose so I could roll it around and have it blow directly on me, which ended up meeting my needs though it got a bit agravating after a while, and still came along with high electric usage. I'm much more happy with the window unit I have, and am going to actually move it from the window I have it in currently to the wall itself- I'll cut through the brick and wall, frame in a sleeve and get it watertight, and put in a nice arbor with something that can stand a little heat a bit out from it in order to camoflauge the install. The cost for the window unit I purchased with both heat and air was just about the same as what I spent for the unit that needed venting, just under $500. Had to run a 20 amp 220 circuit for it, but was able to do that myself. Ended up with heating and cooling both, and my electric usage is about 1/3 of what it was previously (not 1/3 overall, 1/3 of what I saw the electric bill increase by that I estimated was related to adding the A/C unit), while maintaining a comfortable temperature level throughout the garage/shop. Obviuosly, the climate you're in can make a big difference to the situation, but if you're having to pull in outside air and that's coming in most of the day at 90 degrees plus, expect to be running your unit quite a bit. And on a side note, the rollaround unit has found a home on our trailer we keep all our camping equipment loaded with, and does a marvelous job cooling off our big cabin tent when we can manage to get away for some camping!!
