With the UK experiencing record-breaking summer temperatures, it is not unusual to wonder if the urban myth that dehumidifiers can cool a room is true. As a country in the northern hemisphere, the UK typically has a temperate climate with warm summers and cool winters. Our homes are geared up to retain heat rather than release it to guard against long, cold winter months.
It is only recently that the question of whether dehumidifiers can effectively cool the air in your home to give you a bit of relief during a short hot summer and whether they are a more cost-effective option than buying an air conditioning unit.
While an HVAC expert and homeowner with a dehumidifier can have a ‘heated’ argument over whether or not a dehumidifier will cool a room, in fact, rooms running a condensing dehumidifier can feel cooler even if the temperature gauge says otherwise.
Why a dehumidifier won’t cool a room
According to the 2nd Law Of Thermodynamics, dehumidifiers wouldn’t be able to cool down the air in your rooms. However, there is no denying that rooms do feel cooler when you run a dehumidifier.
Running any electronic device, such as a TV or desktop PC, will always raise the air temperature in the room. Even running an air conditioning unit will generate heat that will circulate in the room unless you have an effective heat exchange between the indoors and outdoors.
Air conditioners must be vented to expel warm air outside and draw fresh air into the room. Dehumidifiers work to reduce the air humidity levels in your rooms, but they don’t need to have a heat exchange and be vented to the outside. This means that the heat generated by your dehumidifier will remain in the room.
Using this logic, you can confidently say that dehumidifiers won’t cool the air in a room. Any HVAC expert will tell you that running a dehumidifier will raise the temperature in a room rather than reduce it.
Why does a room feel cooler when running a dehumidifier?
Dehumidifier owners will tell you that their rooms feel cooler when running a condensing dehumidifier but may not know the reason why. For example, if you switch on a dehumidifier in a room that measures 26 Celcius, after running for a while, the temperature in the room may rise to 27 or 28 Celcius.
However, the air in the room will feel more like 25 Celcius. This raises the question of whether we find it difficult to sense the actual temperature when close to a dehumidifier.
Changes in the humidity level in the air in a room can help you feel cooler rather than the dehumidifier cooling the room.
In an experiment where a dehumidifier was run in a room for a few hours, the room temperature increased by a degree, but the relative air humidity was lowered by 30 per cent.
The room felt cooler because of the lower relative humidity level, which can affect how we regulate our body heat. Humans regulate body heat by releasing moisture through the skin that evaporates and cools the skin’s surface.
We sweat more when we overheat to cool us down. But the amount of sweat we release and the evaporation process will be in balance with the humidity of the air. The air is highly saturated with water in hot, humid air at 70 per cent relative humidity. This makes skin moisture evaporation more difficult.
Reducing relative humidity
Reducing the relative humidity in a room in your home makes it easier for your skin to evaporate sweat and cool you down. Let’s say you reduce the relative humidity of a room to 40 per cent. The air around you will be less humid and absorb moisture from skin evaporation much easier, making you think the room is cooler when it is not.
Thanks to dehumidifiers reducing the relative humidity in the rooms in our homes during those few sweltering summer weeks, we can feel more comfortable and get a cooling sensation when we enter a room with a dehumidifier running.
As the weather in the UK tends to lean towards many months of cooler weather and sometimes a few weeks of scorching temperatures, it may be a more cost-effective choice to buy a dehumidifier rather than spend a lot of money on installing air conditioning in your home.
So to summarise, the feeling that dehumidifiers cool down rooms in our home has:
- Nothing to do with changes in room temperature
- Everything to do with changes in relative humidity in the air
- At low relative humidity, 40 per cent, for example, our skin evaporation is more effective at cooling the body
There is no doubt that people believe that dehumidifiers help to cool down rooms, but in fact, they can raise the room temperature. As we explained in our article: Can a dehumidifier warm a room? You can use a dehumidifier to take the chill out of the air in your colder rooms or hallways, especially if you choose a desiccant dehumidifier.