As our planet is getting warmer, more and more people are considering getting an AC. Those who own a home often opt to get a central AC - a unit that attaches to the houses furnace and channels cold air via the floor vents to cool the entire house, as opposed to installing individual AC devices in each room. 

Keeping the entire house cool 24x7 is cool in both senses of the word, and seems like the sensible thing to do…but it is? Today I'll be making the case for the opposite solution.

The main driver for writing this piece is that my state is going through a major heat wave now, and it is slowly becoming a regular thing. Every time we have one, the central AC systems used by many people and business craps out, as these systems were not designed to handle continuous 100 degree heat for several days. The result is that the people who repair these things are insanely overbooked, and anyone whose unit has stopped working might find themselves waiting for several weeks for a repair. Similarly, anyone who is now baking in this heat and wants to have a unit installed might find themselves waiting until September or even October to book an install. Quite unfortunate.

I, on the other hand, have chosen to adopt a model similar to the RAID concept used in computers. When building servers, it is customary to install a set of simple and cheap hard drives, rather than one large and expensive one. RAID stands for "Redundant Array of Inexpensive Disks". The idea is that each drive costs about $100-200 and isn't large, but when you put 8 of them together, you get a lot of space. Not only is this cheaper than a much-larger single drive, but also provides redundancy. The data is programmatically spread across all the drives, so that if one of them fails, the others "step in" and no data is lost. In the case of air conditioning, I also opted to buy three simple window AC units, each costing about $300, and have one in each room of my house. Installing a central AC would have cost at least $6000, and possibly as much as $9000, as my furnace and vents are old from 1961 and would probably need to be replaced or upgraded significantly. And as I noted above, having one central unit also is a risk for it being unable to handle the crazy weather and leaving me stranded with zero cooling for weeks. 

Another advantage of individual units vs central is the fine-grain control, as the cooling can be tuned differently in every room and part of the house. For example, if your house has two floors, then the top floor typically receives more radiation from the sun and gets hotter. The AC will blow the same amount of air into each room, so depending on thermostat settings and where the sensor is located, it might either have the bottom floors nice and cool, but the top floor will be too warm, or it might keep the top floor nice, but the bottom floors uncomfortably cold. Similarly, if grandma is living with you, then the 69-70 degrees most people like might be too cold for her bony ass, putting either all of you at her mercy, or vice versa (I've seen people who literally have a space-heater on in one room at their AC-cooled house!). 

A counter-point that was brought up is the fact that central AC units are designed to be more efficient than individual ones, so it would consume less power than running multiple individual units. In theory, if you were indeed running individual ACs in each room, 24x7, then that's true. However, if there are 2 or 3 people living in a large house, then they don't need all of it cooled, certainly not 24x7. With individual ACs, they can turn each on or off and set different levels of cooling based on their actual needs (and today, with Google Home and Alexa, you can easily control all of that with your voice, as well as timers and "routines"). Rather than waste all that electricity cooling a room you might rarely be-in, or during times when you're mostly not at home, you can set it to be more specific and save a lot on energy. The price for this, of course, is the need to manage all of this, and the fact that if you only remember to turn the AC on when you walk into a room, you might need a few minutes until it cools down. 

Naturally, the bigger one's house is, the more challenging it can be. If you live in a 5000 square-foot house, it can be unreasonable to have to buy 15 AC units, and another factor is noise, as individual units are typically more noisy as well, and can be quite an eye-sore, both from the inside, as they block a big part of the window, and from the outside of the structure (some HOAs may even forbid these). But for smaller places with good room separation (unlike big, open-space), I vote for individual units. Disagree? Comment here and convince me!