Do you run your wall AC unit constantly?
July 8, 2018 8:18 AM   Subscribe

My new apartment in LA has wall AC units, and I'm wondering if they're meant to run all day (even while I'm at work), or if they should only be turned on while I'm at home. All of my previous apartments had central air.

I've seen these threads, which gave me an idea, but I still have a few more questions:

1) Given that LA's heat is dry, is it safe to leave the units off during the day? In my previous apartments, which had central air but were in humid areas, I was cautioned against this to prevent mold.
2) Are there any other non-economic considerations behind leaving the units off during the day?
3) Am I correct in understanding that, if I just keep the fan on all day, it won't do anything to actually cool the apartment?

I would prefer to leave them off while I'm out during the day in order to save energy and lower my electricity bill. If it helps to know, the apartment is small - about 500 sq ft - and has about 10' ceilings. The windows are closed and covered during the day. No pets. There are two rooms, each with its own unit. I myself run cold and can tolerate higher indoor temps, so I don't expect to need much adjustment if I were to I come home to a warm apartment.

Thank you everyone!
posted by aquamvidam to Home & Garden (15 answers total) 2 users marked this as a favorite
So, we've got a monster in-wall unit here in Cambridge, MA (where the heat is very much not dry, witness this last week's nasty heat wave that felt like walking through a swamp), and we generally leave it on when the weather is hot. If we're out of the apartment, we crank it up to 80-82F, and then crank it down to 70F (which means the apartment gets to about 75F) when we get home. The building is a bit of a concrete bunker, so it holds heat bad otherwise. In your case, you probably can leave it off safely if you're ok with coming home to a really warm apartment, but there's a question as to how quickly your ACs will be able to pull the temperature down. Probably the best way to figure that out is by experiment.
posted by Making You Bored For Science at 8:22 AM on July 8, 2018 [1 favorite]

I’m dont know what you’re supposed to do but my andecdata is that when I lived in Togo in West Africa people (in cictieswoykd could afford them) would just run them in their office or bedroom while they were in it (or a bit before) and then leave them off the rest of the day. Especially in a place with dry heat it seems it would be fine to leave them off during the day.

Leaving on the fan all day won’t keep the place any cooler really but it does help a bit with stale air (IMO)
posted by raccoon409 at 8:35 AM on July 8, 2018 [1 favorite]

For your question 3--correct, fans don't lower air temperature, they make you feel cooler by helping to evaporate sweat from your body, so leaving it on when you're not home does nothing but run up your electric bill.

In my experience with window ACs, they are generally targeted for one room and it really doesn't take very long to get the temperature down to a comfortable level, so I always left them off (or on at a higher temperature for my dog, about 78.) Never had any trouble with either of these, except that in the latter example my electric bill was higher (obviously.)

If I were you, I'd leave them off during the day.
posted by Automocar at 8:40 AM on July 8, 2018 [4 favorites]

Lifelong Angeleno here, saying you absolutely do not need to run them to prevent mold. Unless your apartment has some particularly special humidity or preexisting mold issues, it's way too dry here to worry about that.

Because we almost always -- not this horrendous week, but usually -- have markedly lower temps at night, you may find it nice to run the fan at night or in the mornings before you leave, to draw in some cool, fresh air from outside. But I'd leave them off when you're not home.
posted by BlahLaLa at 8:46 AM on July 8, 2018 [1 favorite]

From a civic-minded point of view, I would leave the AC off when you're not home. The grid gets overloaded in extreme heat situations when everyone has their AC on (like Friday here in LA!) and this result in blackouts, which really sucks in the heat.
posted by queensissy at 8:51 AM on July 8, 2018 [3 favorites]

AC uses a ton of electricity. I would leave it off when you're not at home. It'll take ten minutes when you get home to cool down your apartment.

(My wife, who grew up with AC and in a place with very high electricity rates, would probably kill me if I left AC in an empty apartment all day.)
posted by JamesBay at 8:59 AM on July 8, 2018 [2 favorites]

Your last paragraph describes my living situation exactly, except that I’m on the east coast sonit is sometimes humid. In my opinion it would be ridiculously wasteful to leave the AC running when I’m not there. Even upon coming home after a weekend away, it only takes ten minutes for the AC to bring the room temp down to a comfortable level.

In addition to the hit to your electric bill, running your AC constantly when you’re not there will presumably result in more wear, and having to repair or replace the unit much more quickly than otherwise.
posted by ejs at 9:11 AM on July 8, 2018 [1 favorite]

Ideally* I set it high when I leave and turn it down when I come home, then high (but not as high) when I go to sleep. "High" is 76° for me, because I have a piano that doesn't like temperature extremes, but if I didn't have that, or a pet, or some other excuse, I'd keep it higher when not around. I have an efficient unit, so it only takes minutes for the temp to come down. Obviously, the higher you keep it, and the weaker your unit, the longer it will take to come down, so you might want to experiment to find a good off-line temperature maximum. If the rooms are distinct (closing the door to one means it doesn't get much air from the other), you might also want to experiment with different usages for the different units. A week of experimentation could have a big payoff in terms of electricity bills, even in as short a period as a month.

* In practice, due to memory and other issues, I am far from "ideal", but that's another story.
posted by ubiquity at 9:27 AM on July 8, 2018 [1 favorite]

Mold is generally not a concern in a normal apartment in LA (normal meaning that it has standard ventilation, doesn't repeatly flood, etc).

Since you don't have pets, I would definitely turn the unit off during the day. If you find that it's unacceptably hot when you get home or that food is spoiling too quickly, I'd set the a/c to around 85 while you're out. Either way, I'd also close the blinds / drapes / shutters to any windows that get direct sun - that makes a surprising (to me) difference in keeping a room cool.
posted by insectosaurus at 9:37 AM on July 8, 2018 [1 favorite]

In addition to the hit to your electric bill, running your AC constantly

...may be annoying your neighbors.

Just open some windows, in the morning, before you leave -- or maybe even, the night before.
posted by Rash at 10:01 AM on July 8, 2018 [2 favorites]

I would never run my AC constantly in any of the climates that I've lived in, including when i live in Los Angeles. Mostly it was a cost factor but also because it's not necessary.

The only room where I ever worried about mold is the bathroom and I just made sure to use the fan/heat lamp in there while showering and leave it on for at least 10 minutes afterwards to make sure the moisture cleared out. AC units are really meant for the room that they're in an not the entire apt though there have been days where I would place box fans in doorways in order to circulate the cold air (only on very hot days) but again, that had nothing to do with mold and was only something I did for short durations in order to get some relief from the heat during the hottest parts of the day.
posted by acidnova at 10:26 AM on July 8, 2018 [1 favorite]

Thank you everyone for your replies! I'm reassured that I can safely leave the units off all day. I have noticed that the wall units are quite noisy, as some pointed out, so there's another reason to leave them off.

Thank you again everyone!
posted by aquamvidam at 10:29 AM on July 8, 2018

If you have older/underspecced wall wiring, running a large one nonstop can heat the wire up enough that it burns through.
posted by Candleman at 11:34 AM on July 8, 2018

I run mine on "dry" to keep the humidity down. It seems to mean they fire up quieter and less often than when they're running on "cool" but it still stays cool enough.
posted by lagomorphius at 12:45 PM on July 8, 2018

I also turn it off when I'm gone. If it's really hot when I get home, I turn it on, take a shower, pat dry, then stand in front of the AC. Ask your doctor first if you have a medical condition because you will get REALLY cold really quickly.
posted by AFABulous at 2:56 PM on July 9, 2018

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