Will a dehumidifier cool a room?
Dehumidifiers and room cooling is quite a paradox. It has been at the center of urban myths for so long that we really need to clear up if a dehumidifier can cool a room.
If you ask an HVAC expert and a homeowner ‘Does a dehumidifier cool a room?’, you will get two different answers:
- HVAC Expert: ‘No. I’m sure a dehumidifier doesn’t help cool a room. In fact, it can heat a room’.
- Homeowner: ‘Yes. I’m sure a room with turned-on dehumidifier feels cooler’.
Now here is the interesting part: Both the HVAC expert and the homeowner are right.
In short, based on the 2nd Law Of Thermodynamics, dehumidifiers couldn’t possibly cool down a room.
But every room does feel cooler when you run a dehumidifier, right?
Let’s clear things up using thermodynamics. After that, we’ll look into why it feels that a dehumidifier cools a room.
Can A Dehumidifier Cool A Room? No.
If you run any electric device in an isolated space (a room, let’s say), it will always raise the room temperature. TV, computer, even an air conditioner, and a fridge will raise the room temperature if there is no heat exchange between the indoor and outdoor.
Every air conditioner has to interact with the outside to decrease the room temperature; that’s why you always have to vent it.
A dehumidifier’s job is to reduce indoor relative humidity from 50% – 100% to 30% – 50%. To do that, it doesn’t need to have any heat exchange with the outdoors. Hence, all the heat created by running a dehumidifier will not be able to leave the room.
Consequently, we can answer ‘Will a dehumidifier cool a room?’ with a definite ‘No.’.
Even the biggest commercial dehumidifiers don’t cool a room.
In short, a dehumidifier is an electric device that (besides everything else) also produces heat. In an isolated room, heat can’t escape. More heat in a room will increase room temperature.
Every physicist and HVAC expert is crystal clear on the dehumidifier raising the room temperature.
Now let’s look at why we all feel like a room with a dehumidifier running is cooler:
Why Does It Feel Like A Dehumidifier Can Cool A Room?
If you put a dehumidifier in, let’s say 80°F, and run it long enough, you will eventually measure 82°F room temperature. However, the real paradox kicks in when your experience is that the room with a dehumidifier is cooler. It should be closer to 78°F than 82°F.
Do we all of a sudden lose the ability to estimate temperature changes when close to a dehumidifier?
Well, kind of, we do. The reason for the ‘Does a dehumidifier cool a room’ is the relative humidity levels. A dehumidifier’s primary effect is on the humidity levels.
Here is an example of what happens if we put one of the best basement dehumidifiers in a room or basement an leave it on for a few hours:
- It decreases relative humidity from 70% to 40%.
- It increases room temperature for 0.3°F.
The reason why we feel that dehumidifier lowers room temperate is exclusively due to the change of relative humidity (30% change in our case).
Skin Moisture Evaporation Is Changed When We Change Relative Humidity
A normal human body temperature regulation includes the evaporation of moisture from our skin. For example, when our body is overheating, we sweat profusely; this is simply a human body regulation to cool us down.
To achieve the cooling effect, the skin moisture (sweat) has to evaporate. This evaporation process is directly proportional to how humid it is.
In the case of high humidity – let’s say 70% relative humidity – the air is already highly saturated with water. That means the evaporation of moisture from our skin will be more difficult. We won’t be able to cool down because of the high humidity.
We have all experienced this. In humid weather, it’s impossible to cool down. Our body sweats profusely, but the sweat can’t evaporate anywhere, leaving it hot.
What happens if we use a dehumidifier to lower the humidity to a comfortable 40% relative humidity?
All of a sudden, the moisture on our skin will be able to evaporate again. The surrounding air, being less humid, will take moisture from our skin much more willing. In effect, our cooling system will work again.
That means that our body has an easier way to cool down at low relative humidity (thanks to the dehumidifier). The net effect – what we feel when the dehumidifier is actively decreasing the air moisture levels – is a cooling sensation.
Answered: Dehumidifiers Don’t Cool A Room Down, But We Feel They Do (And That’s Completely Normal)
Feeling that dehumidifiers cool down a room has:
- Nothing to do with changes in temperature.
- Everything to do with changes in relative humidity.
At high relative humidity (70%, for example), the moisture from our skin – our cooling system – has a hard time evaporating.
When we use a dehumidifier to lower relative humidity (to 40%, for example), the evaporation of moisture on our skin is much easier.
The effect of that cooling system working again is that we will think that the room temperature is lower due to the dehumidifier’s action.
But the reality is that the temperature does not change significantly. The capability of our body’s cooling system via sweat evaporation is increased at lower relative humidity. That is why it feels like a dehumidifier can cool a room.