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?

  • 1
    You mean "dehumidifier".
    – ChrisF
    Commented Oct 5, 2010 at 12:03

7 Answers 7


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.

  • 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-
    Commented Oct 5, 2010 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.
    – user45
    Commented Oct 5, 2010 at 13:31
  • 1
    +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. Commented Oct 6, 2010 at 15:33

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.

  • 1
    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. Commented Jul 26, 2012 at 7:26

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!


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.


I would get a portable A/C unit with dehumidifier option. The thing no one mentioned is that an A/C and dehumidifier are almost the same thing. The difference is an A/C unit separates the hot and cold air, sending the hot air outside and the cold inside. The dehumidifier blows the air across a cold coil where the water condenses and than across the hot coil returning warm dry air to the room. A/C units also remove water but the water that condenses is either blown outside as vapor or drips out of the unit. The reason I said portable A/C with dehumidifier is during the summer you can remove the water and stay cool. During the winter you run it as a dehumidifier so you don't cool your space during winter.

  • Thanks! :) In time though I bought both an air conditioner and a dehumidifier (because the air conditioner doesn't offer water removal - it just blows it out the other end). And I'm quite pleased with the results. :)
    – Vilx-
    Commented May 10, 2015 at 10:11

Don't ever make my mistake. I bought a portable A/C with dehumidifier option ( Delonghi ) with the hope that it can cool me in summers and dehumidifi in winter. But the fact is it gives cold wind in winter, not as cold as it gives in summer but it decreases the room temperature significantly. So because it is winter now i had to go and buy a dehumidifier unit , dehumidifiers give +2 degrees of room temperature but A/C units give -2 degrees of room temperature. And it's because of the logic of their designs. They work by same principle but different logic.

  • Well, there's hot air coming out one end of it. Can't you make that blow back in the room too? The net gain should be positive then.
    – Vilx-
    Commented Feb 22, 2017 at 9:18
  • @vilx - Many portable re-evaporate and blow most of the condensed moisture out the hot end. If you don't send it outside then the moisture will stay in the room.
    – Johnny
    Commented Feb 22, 2017 at 16:47
  • Ahh, in that case, yes. Bad design.
    – Vilx-
    Commented Feb 22, 2017 at 17:40
  • @Vilx- - Well, it's good design for the normal use case - it increases efficiency by evaporating the water from the hot-side coils and it exhausts the water outside so you don't have to drain the unit. Though in very humid environments, the unit still collects water because it can't evaporate it all.
    – Johnny
    Commented Feb 22, 2017 at 20:51

To use a portable AC as a dehumidifier during the winter I think you would need to remove it from the window place it on a level surface and run it so it blows both sides back inside the room. Then you only need to pipe the water drain through the wall with a rubber hose and a clamp. My theory that the a cold air that blow from the front side equal the warm air that comes from the back vent. If you leave it in the window then you blow the warn air out the window and the temp will drop significantly.

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