Hello: I am renovating an office that is in my garage. The space is about the size of a parking space (sorry - don't have measurements in hand). I'm a professor and use it only sporadically - most days in the summer, most days in January, and on and off the rest of the year, depending on what I'm working on. It currently has an ancient wall AC unit that barely works (though the brick garage stays quite cool in the summer and there are big french doors to the garden so I don't use it much anyway). It has ancient baseboard heaters some of which are hidden behind shelving units and cost a fortune to run (my January electric bill is the highest of the year). My contractor has recommended a mini split unit instead of a new AC unit and new, relocated baseboard heaters. My question is: is this worthwhile even if I don't use the AC very much? Also, I have read that the heat pump aspect of the minisplit unit doesn't really work in sub-freezing temperatures. January and February are exactly when I most need heat and in Washington DC it is certainly below freezing during those months. In other words, my main need is for heat not AC - it can be REALLY cold out there on a January morning! does it still make sense for me to install a minisplit? what do I need to know to get one properly installed? Many thanks Jess

If your current ductwork can handle the airflow required of an air conditioner matched to your home's needs (you NEED a load calculation to determine size requirements), I would consider installing a split air conditioner (not heat pump) and indoor coil to go with your existing furnace. There are variables involved, and ductwork/airflow is especially of importance in this case, especially in older homes (how old is your home?). Higher efficiency furnaces/air conditioners/heat pumps need more airflow than older systems, resulting in problems in retrofit installations with undersized ductwork. As I've said before, ductwork is an often overlooked element of the installation but is extremely important in overall comfort/efficiency. Unfortunately not all contractors are well versed with duct sizing, and with existing ductwork systems in older homes, it's often impracticle to change the ductwork. But with a load calculation and envelope improvements, oftentimes a knowledgable contractor can provide a good solution. Another possible option would be ductless minisplit systems such as Mitsubishi's Mr. Slim system. They work very well and I believe in the product, but if you have existing ductwork I would try to go with central a/c. Have you gotten any estimates yet? What is the model/information of your current furnace? Full model number preferred -- should tell us your blower/heat capacity. This post was edited by ryanhughes on Thu, Feb 14, 13 at 13:50

OK, first to worthy: Believe it or not, statistics are one thing, but reality another. My cute little 5000 btu adequately cools the SW bedroom as well as the larger living room nearby. I sorta shiver when I go in there. ...The identical AC adequately cools both the SE kitchen, and even somewhat extending into the NE room where I sleep. Any cooler, and I'd get sickened, due to my health condition which causes me migraines and achiness in cold/dry temps. Which is why for me, a quite-distant 5000-btu set on high, is perfect. Furthermore, I have it on a Brinks timer, where it's on awhile, off awhile, on awhile, off awhile. To Ionized & others: Actually (as stated above) I had already had a handyman build a wall fan into the wall. Problem is, the current fan is cheap plastic and very weak. But if that cheapo fan were replaced with a high end one, it could circulate the AC air from SW b.r. into the NW master b.r. can it not? Now, regarding the 10-by-10 north-facing b.r. which has stupid sliders all along the north wall. So what to do about that? So my question is, if I put a high-power AC into the wall in the spot where the attic-fan switch is (see pic of NW master b.r.)... ...would that reach down the narrow hall all the way to 10-by-10 north-room too, if I close the bathroom door? In which case, the problem is solved. Because I'd have one AC for SE kitchen & NE b.r. (works fine) the other AC for SW b.r. & living room (works fine) finally, a larger AC for Master b.r. & 10-by-10 north room ......with both bathroom doors closed (or need they be? If you analyze my layout carefully, do you agree to that as a solution? Would there be problems with putting the AC where the attic fan switch is? (The fixture has both the switch, and an outlet in it). Also, as you can see, that pitiful strip of wallspace is only 20 inches, so can an adequately powered AC be put in there, so as to reach the fairly distant 10-by-10 room down the hall? Lastly, would Central AC be cheaper than running three ACs?

They've GOT to be better than window/wall units, plus no ducts running through HOT attics, dropping your laboratory-measured 16 SEER to a real-life 11. ;') OTOH, though the condenser+compressor are now outdoors, you still have fundamental issue with the warm return-air and the cool outflow-air being co-located... but, apparently this problem has been engineered away to a significant degree. It is very difficult to find someone who is NOT happy with their "mini-splits", though correct sizing and installation are still paramount... as is patching up the huge holes left by the window units. ;') I wonder if Brickeyee could provide the details on how his noisy units are MOUNTED in his industrial setting, i.e. perhaps on exposed metal studs, uni-struts, or some similarn base that does not dampen vibration? One does not hear the noise complaints from residential users.