Does a dehumidifier cool a room?
By The Damp GuyLast updated
No. It does the opposite, slightly. The manufacturer's own figures are that the air leaving a compressor dehumidifier is about 2°C warmer than the air that went in, and the air leaving a desiccant one is about 10 to 12°C warmer. So if you are hoping to take the edge off a warm room, this is the wrong machine.
The reason is worth thirty seconds, because it also explains what a dehumidifier is for. Look at an air conditioner and you will find a part of it outside: a box on a wall, or a fat hose shoved through a window. That is not decoration. It is how the heat leaves. An air conditioner moves heat from in here to out there.
Now look at a dehumidifier. All of it is in the room with you. There is a water tank, a plug, and nothing going outside at all. Nothing it does can move heat out of the room, because it has no route out. It takes water out of the air, and the electricity it uses to do that ends up in the room as warmth.
So the two machines are answering different questions. One makes a room colder. The other makes it drier. They get confused because both produce water and both hum, and because a lot of pages answer this question without saying which type of dehumidifier they mean.
The two types give genuinely different answers
This is the part most pages skip, and it is the part that matters if you already own one. There are two kinds of domestic dehumidifier and they are not variations on a theme.
A compressor model, which is the common one, puts out air about 2°C warmer. Meaco is blunt about what that amounts to in practice: it "will not warm up the room the dehumidifier is being used in", and the air will "actually feel cold to touch". So for a compressor the honest answer to the question is no, and also no in the other direction. It is close to thermally neutral in a room of any size.
A desiccant model is a different proposition. Its output air is about 10 to 12°C warmer, and Meaco says that "will have a significant impact on the temperature of the room its being used in". That is the manufacturer describing its own machine as something that noticeably warms a room. If you have one of these running in a small bedroom and wondering why the room is stuffy, that is the answer.
Which is worth knowing before you buy rather than after. In a cold space the desiccant is the right machine anyway, and for a mechanical reason: below 10°C, Meaco says compressor models "spend more and more of their time defrosting themselves rather than dehumidifying". So for an unheated garage, a cold back bedroom or a caravan, the warm one is also the one that actually works.
What to do if the real problem is that the room is too warm
Then you want an air conditioner or an open window, and this site is not going to pretend otherwise to keep you on the page.
What a dehumidifier is genuinely for is the moisture, and moisture is a separate complaint that happens to travel with heat in summer. If the reason you are asking is damp, condensation or mould rather than temperature, the machine is right and the full guide to dehumidifiers here covers what one costs to run, how long to run it, and the cases where it is the wrong answer.
And if the thing you are actually chasing is condensation, temperature is still in the story, just not the way people expect. Condensation is decided by how cold a surface is rather than how warm the air feels, which is why a room can be warm and still run with water down the windows. The condensation guide here sets out where that line sits, and the one on heating deals with the related question of whether putting the heating on helps.
One last practical note, since the desiccant's warm output has a use. It is why that type dries laundry quickly, which is its own question and has its own answer here.