Youβve got air leaks. Set your desired humidity higher.
this post was submitted on 13 Jun 2025
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Technology Connections recently posted a detailed video about dehumidifiers that's worth watching. But a key takeaway is that on an AC, the hot side is outside (making the inside cool), while in a dehumidifier they are directly next to each other (condensing the moisture).
Without looking into the specifics, my guess is that it's not routing the cold air over the hot side to keep things inside the same temperature.
Sounds like either a) the dehumidifier is broken or confused b) your apartment has more moisture in it than you thought or c) the moisture is being replenished from somewhere.
I stayed in a friends house a few months ago and she had 4 dehumidifiers running since she bought it. The house was built before damp proofing was a thing and set into a hill, so the place is basically one massive wick for groundwater. It will never be over for her.
I'm curious if it actually has a humidity sensor or what the humidity is set to. In Florida it's basically impossible to get a dehumidifier to 35% and 40% is possible under certain conditions.
If the apartment is getting colder it will be harder to extract water from the air because the air can't hold as much water
Dehumidifier mode probably runs forever regardless of temp.
:((
Just use the temp setting. AC already dehumidifies.
To could also get those bags of beads that absorb water and hang a few in the worst parts of the house. My mom has a fancy one that you can plug in to dry it out, but that just shifts the humidity unless you dry it outside.
Unless thereβs a humidity setting, I would assume so.
Good point, didn't think of that.
... what @Thorry84@feddit.nl said!
That's not how AC works at all.
AC works by evaporating a gas, evaporation (going from liquid to gas) takes a lot of energy. By dong this inside a ribbed evaporator, the energy gets extracted from the evaporator cooling it down. Then a fan ventilates the air in the room over the evaporator, which in turn extracts the energy from the air. On the other side the AC has a compressor which turns the gas into a liquid. This takes energy to do, so the compressor puts all that energy in, heating up in turn. A large condenser (looks like a radiator) is used to cool the coolant down. The compressor puts in energy in the form of pressure, but as the gas is hot it can't turn into a liquid. By cooling it down in the condensor it can turn into a liquid. A fan is used over the condensor to dump the energy from the gas into the outside air.
For gas in the past something like R134a was used, these days something like R290 (propane, but very pure/clean) is used which is better for the environment. In a very real sense ACs are energy pumps, they take the energy from inside and dump it outside. But they can also work the other way around, taking energy from outside and dumping it inside. This leads to pretty cool effects where you can heat your home with more than 100% efficiency. Because the energy you need to put in is only the overhead for pumping the energy, but the amount of energy being pumped can by much much larger. Over 100% efficiency in a closed system isn't possible, but since an AC dumps the energy in the outside air it isn't a closed system. ACs are also known as heatpumps for this reason.
The way an AC can be used to dehumidify is because of the dew point in the air. This is a combination of the amount of moisture in the air, the pressure and the temperature. When the AC pushes the temperature from above the dew point to below, the air can't contain all the moisture it contains. This will cause the water to condens on the evaporator in the AC. This can (and probably will unless you are in a very dry area) occur during normal cooling operation. This is why there are normally lines to take the water and get it out of the AC unit. When the water would remain, it's a breading ground for all sorts of nasty stuff (look up legionnaires disease), so it's important to get it out of there. A lot of times a small water pump is used to pump the water away.
When cooling the AC tries to regulate the amount of energy pumped to keep a constant temperature in the room. Older/cheaper ACs just do this by start/stop, but better more modern ACs can regulate their power to prevent big swings in temperature and save energy. But when in dehumidify mode, the only purpose is to push the condensor below the dew point. Now the AC could do all sorts of fancy calculations to figure out the dew point and get it there. However that isn't done at all, most ACs just push the temperature down as hard as they can. This is because the further you get down below the dew point, the more water condenses, so it gets the moisture out faster. And it's also really complicated to calculate the exact dew point and get the measurements, because the AC itself influences the measurements a lot, so it would need sensors further away. Some big systems can do this and also measure the amount of moisture in the air and regulate to that. But small systems people have at home usually just go as hard as possible.
This is the reason why it just never stops in dehumidify mode and the air gets colder and colder. Nerds can probably get something cooking with sensors and homeassistant, but regular home systems won't go to a target when in dehumidify mode. There are hard limits to how cold it will allow the condensor to get, to protect the system and prevent frost, but that's not really the same as a target temperature in cooling mode.
Some better ACs also have a smart dehumidify mode, where it closes the inside unit, turns off the fan. Then cools down the condensor a huge amount. Then opens the inside unit and slowly blows air. This way it can get a lot of moisture out of the air fast and not cool down the air a lot at once. But in the end it's the same effect. The energy still comes from the room, so the room will cool down, it will just not have huge swings in temperature.
My guess is your heat pump doesn't have a good dehumidify mode. The thermostat does, but it's just turning on the A/C. A good dehumidify mode is a very slight A/C and moves a lot of air. So, if your compressor doesn't handle enough steps down, you're spending a lot of electricity for not much effect. A dehumidifier with a continuous drain might be a better solution for you.