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I live in a flat in an older house and I have the disadvantage of living next to an outer wall. In autums/springs there is a period when the central heating isn't turned on yet, but it's already getting cold outside. During this time the wall (and generally air inside) gets quite moist and mold starts forming. Also the moist air makes it feel much colder than it really is (the thermometer shows 20C, but it feels like 15C).

Thus I'm looking at dehumidifiers and air conditioners. The first are cheaper by half, the latter are more powerful (according to spec) and can also be used for cooling the air in the summer.

But I really wonder how much I can trust the spec and how much it would really help. Does anyone have any experience with this?

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You mean "dehumidifier". –  ChrisF Oct 5 '10 at 12:03
    
@ChrisF - Yes, thank you! Changed the text. –  Vilx- Oct 5 '10 at 12:53
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4 Answers 4

I would consider a dehumidifier which will pull moisture out of the air. I'd also check into why the wall is getting moist. Are you sure there is enough insulation in the wall, because you definitely should not have moisture condensing on or in the walls.

An air conditioner will make the room colder which you probably don't want if the weather is already turning cold. The dehumidifier will pull the moisture out of the air without cooling the air the way an air conditioner would.

For the time being the dehumidifier should pull moisture out of the room for you. The specs for the appliances (dehumidifier or air conditioner) are usually fairly accurate, most notably on larger name brands. I've found knock-off and smaller brands to be a bit sketchy when it comes to performance, so I've learned my lesson and usually go for the larger more established brand names when it comes to things like this.

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The wall is bare reinforced concrete inside and out, no insulation whatever besides about 15cm of iron and cement. Well, as far as I know. Some of neighboring houses have received extra insulation on the outside, but mine is still waiting for the necessary budget. And for various reasons I can't make more insulation on the inside right now. As I said, some air conditioners include a "dehumidification" mode of operation as well. I don't intend to cool my room. :P –  Vilx- Oct 5 '10 at 12:58
    
@Vilx ahh ok ... I've actually never had a window mount or portable air conditioner, I've always had central air so I didn't know they had a dehumidification setting. –  Scott Vercuski Oct 5 '10 at 13:31
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+1 for mentioning insulation - this is likely the real problem. The wall is getting cold enough that it's below the dew point of the air inside the house. –  Eric Petroelje Oct 6 '10 at 15:33
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Every air conditioner I've ever seen works not only to cool the air but also to pull moisture out of it. That's often why you get dripped on when you walk underneath a window unit. There might be condensation on the cooling coils, but more often than not the "conditioning" of the air includes bringing it down to a comfortable humidity: literally pulling moisture out of the air and draining through a pipe -- often that part of the a/c's job is more important than altering the temperature in terms of comfort.

So yes, an a/c will be more expensive than a dehumidifier, but that's because it does both jobs: cooling and reducing moisture in the air. I'd go the double-duty air conditioner route, but then again, I live in Florida and we really can't get enough a/c down here!

Also, I've seen dehumidifiers in action and I wasn't impressed. You usually have to manually empty the water collection area, and even then it really doesn't do all that great of a job lowering the humidity.

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a dehumidifier actually does 3 jobs by your definition: cooling, reducing moisture in the air, and warming the air back up again, something desirable in this case since Vilx is complaining about the cold. –  Philip Ngai Jul 26 '12 at 7:26
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I use my Sharp portable AC to dehumidify my man-cave/office fairly often, it works really well - and doesn't require any condensate drains or tank emptying nonsense.

Really all the machine is doing is running the AC at a minimum setting to remove the moisture from the air, but this is the most effective method of dehumidifying a room - short of purchasing a dedicated dehumidifier which realigns the airflow path across the condenser and evaporator to give you warm/dry air.

Or as a second alternative - buy a pallet of desiccant packs and spread it around the room :) In all seriousness - I actually do something like that in my motorhome (I bought a big desiccant holding "bucket" from West Marine and it does a decent job keeping the dampness out, but you have to replace the pellets and drain the water periodically, so it's kind of messy).

Good luck!

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Just for a more concrete example, we have a portable air conditioner in a 15'x15' finished room (in a fairly new house) that's currently filling a 5-gallon bucket every 12 hours (currently investigating draining it to the outside), so using them as a dehumidifier will certainly work. Ours also has a mode to dehumidify without cooling which seems like what you were interested in.

Dehumidifiers tend to produce a fair amount of heat, which is fine if you're only worried about cool weather. If you think you might also use it in the summer then you might want to go for the A/C unit. Even if you weren't going to use the cooling feature, at least you can exhaust the heat it creates to the outside. (I haven't seen any non-A/C dehumidifiers that have exhaust connections.) In the winter you can disconnect the A/C's exhaust to keep the heat inside, and then it really would be just a giant dehumidifier.

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