How can we use our ACs most efficiently?

July 5, 2008 9:28 PM

We have two (okay, four) window air conditioners. How can we best use them to cool our house?

We live in a two-story, 1400 square foot house. It was built in 1895, and obviously they didn't have central air back then, so we use window air conditioner units. We have four of them, but two are kind of old/junky/possibly broken, so we're really only using two.

We've already taken other steps to keep the house cool such as adding extra insulation and vents in the attic, keeping the windows covered during the day, using ceiling fans, and running appliances like the washer/dryer and dishwasher early in the morning or at night.

The first couple years we lived here, we set up one AC upstairs and one downstairs (at opposite ends of the house), and only turned them on when we were in the room. Those were terrible summers.

Last year and this year, we've been setting up both ACs upstairs (at opposite ends of the house), and leaving them on at a low setting all the time. The cool air sinks to the downstairs, and its generally tolerable in the house, as long as you're not doing anything too active (like, say, vacuuming).

Are we using our ACs as efficiently as possible? Is there a different arrangement that could keep our house cooler and/or use less energy?

(For reference, here is a general floorplan - the ACs are currently in the front and back bedrooms upstairs.)

PS: We have three cats, so they need to be comfy all day, too.

posted by LolaGeek to home & garden (8 comments total)

I live in a house built in 1905, so I feel your pain. First thing you need to do is get a fake sliding door at all doorways (more expensive - they are basically sliding plexi glass on a rail) or drape blankets (less expensive) between rooms so that you can maximize your cooling per room. (Take the blankets down when folks come over)My recommendation is only keep one room of the house cool during the day when you are gone. The cats will figure out what part of the house is cool - cat's are really resilant and aren't stupid. Enjoy your summer!
posted by Drama Penguin at 11:36 PM on July 5

Clean the filters!! Regularly. (With three cats you'll almost find enough in there to make another cat.)

Closing/opening doors or better yet making (rental friendly) curtain partitions* (Kitties can just slip through that way.) Then you can concentrate/direct the cold air exactly where you want it. (If there's a wall it will pool, a path and it will flow.)

*To really be effective you need 2 curtains, with a gap in the center. (It doesn't matter how wide really, just as long as they're not touching.) Thumbtack-ed to the top edge of door frame skirting on either side is perfect! (And the landlord will never know it was there!) **

Ransack an extendable pole off something (mop ect.), put door stops at either end and hang a curtain off that if there's nothing else. This one is tricky to get the balance with. Too tight and it was going to ding the walls. Not tight enough - and Loopy would pull it down from dragging his tail in it. If any of your cats like poking their tails in dresses ect. you would probably have the same problem. (The pole works it's just not as simple as thumbtacks in the skirting.)

**PLAIN single sheets, gathered, with the overhang pinned into attractive scallops works best I think :)
posted by mu~ha~ha~ha~har at 12:07 AM on July 6

Your house is similar to ours, 'cept ours was built in the 20th century (1905).

How many BTUs are the A/C units? Are you using window fans for cross circulation? Those, with the ceiling fans, keep our living and dining room nice, while the A/C units control the bedrooms, which are important being able to sleep in the heat. Note that we use two window fans a room, one to draw air to the outside, the other to pull in air from the outside. This creates a nice, gentle breeze in the room, even if their isn't one outside. It also helps to have screens for the front and back door to let air flow.
posted by Brandon Blatcher at 5:37 AM on July 6

Don't just clean the filters, you need to take them outside and blow out the fins with an air compressor. Be careful not to bend them over. If those two junky ones will run (can you hear the compressor kick in?) this is often all they need. Dirty coils not only make the units transfer heat poorly, it also kills the compressor pronto.

I second Brandon's call for the BTU of the A/C units. A common (and improper, but that's a whole 'nother discussion) rule of thumb used in the industry is 500 sq feet per 1200 BTU. This is for central air, and does not take into account things like climate, size of windows, southern exposure, etc. It is a place to start however. Use it to figure out how many square feet each unit is good for, and if you're being realistic in your expectations.

The key thing is airflow. I wouldn't worry so much about efficiency. Efficiency don't mean squat if you can't sleep because you're too hot.

If you ever have a shit pile of money to spend and fix this properly, you could always look at a ductless split like this. They run several indoor air conditioning coils off of one outdoor condensor, with only small refrigeration pipes connecting them (often pulled through the walls of older buildings).
posted by vonliebig at 9:49 AM on July 6

Also, Consumer Reports has a nice calculator for figuring out what size window units to buy. It's detailed and involves some measuring on your part, but it worked out well for us
posted by Brandon Blatcher at 12:02 PM on July 6

We have two small window A/C units that do a pretty good job of keeping our house cool. They also get some help from a window fan that is used to suck hot air out of the upstairs, a dehumidifier to keep our basement drier, and a couple of good fans to help keep the air moving a little bit when we're in our family room or bedroom.

First, I suggest that you start by trying to keep the sun and heat out of your house by keeping your curtains and blinds closed. If you need them, you can get halfway decent vinyl blinds for $6 or $7 a piece.

If you live in a humid area then keep your doors and windows shut even if it feels cooler outside at night. The temperature might be cooler but the air is still probably going to be loaded with humidity that you want to keep out of your house so you'll feel more comfortable and the A/C won't have to work as hard the next day.

If you have any rooms you don't use then keep closed off to them if you can.

Our window fan is designed to suck air out of the house and it runs almost all the time at a low setting. It's on the second floor where the heat rises and it is also on the side of the house that gets the most sun. Besides getting rid of air that is 10 to 30 degrees warmer than it is downstairs, it also helps pull cold air from our upstairs air conditioner over to that side of our house. This fan probably does as much or more than the A/C to keep our upstairs comfortable. It can also be used blow air into the house and I'm sure we paid less than $30 for it.

Once last thing, our air conditioners are too small to cool the house down very quickly once it gets really hot, so we try to give them a head start by turning them on before we really need them.

Good luck from upstate NY.
posted by 14580 at 4:01 PM on July 6

Thanks for the answers so far. Of the two units we're using, I think the newer one is 1200 BTU (bought last summer). The older one came with the house, and I don't know how many BTU it is, but imagine it's about the same.
posted by LolaGeek at 1:02 PM on July 7

Unless your house is very tiny, you need more BTUs. I'm buying an AC unit tomorrow and I'm planning on getting a 10,000 BTU for the entire apartment. It should keep the place livable but not "cool." (This apartment building is also cold). I'd recommend getting a stronger unit and putting it in the room you are in fairly often, ideally one near the bedroom but not right next to the kitchen. This way your bedroom will also be relatively cool, but you won't actually have to have the AC in the bedroom (ACs are noisy).
posted by Deathalicious at 1:42 AM on July 18