When Should I Turn Off A Dehumidifier? Winter vs Summer, 50% RH Rule

“How do I know when I should turn off a dehumidifier? Should I run it in the summer as well as in the winter?”

Dehumidifier can run constantly. Especially in the summer, you set it to 50% relative humidity and forget it. However, there are two distinct cases when it makes sense to turn off a dehumidifier. These are:

  1. When relative humidity falls below 50% in the summer. The key here is that you don’t actually turn off the dehumidifier yourself; it will shut itself off when it reaches the 50% RH you set. When the humidity starts rising to 51%, 52%, 53%, and so on, it will turn on again by itself, decreasing the humidity back down to 50% RH.
  2. During the winter (October, November, January, February, March, even April). Summer months are humid; fall and winter months are usually dry. In living spaces, we can usually turn off a dehumidifier during October, since fall and especially winter months are drier.
what happens if you shut off a dehumidifier too early
Be aware that if you shut the dehumidifier off too early (when you still have 60%, 70%, 80%, even 90% RH), the air moisture can spur mold growth, and moisture can literally eat through the walls.

Here’s the thing:

According to the EPA, the ideal indoor relative humidity ranges from 30% RH to 50% RH. The reason why we are sometimes wondering when to use a dehumidifier – in winter vs summer – and when to turn it off is this:

  • In the summer, we usually have to fight high air humidity levels (higher than 50% RH). That’s why we use dehumidifiers mostly in the summer months (May, June, July, September).
  • In the winter, we usually have to fight low air humidity levels (lower than 30% RH, causing skin itching and so on). That’s why we use humidifiers (units that increase moisture levels; opposite to dehumidifiers) in the winter.

In short, dehumidifiers are mostly seasonal HVAC units (for summer). This is predominantly true for portable and whole-house dehumidifiers in living spaces.

Basement dehumidifiers, however, are another matter altogether. Basements are the most humid spaces in our house. Even in the winter, the relative humidity levels in the basement can be above 50%; that’s why it can make sense to use a dehumidifier in the winter in the basement.

Here is the 101 guide on when to turn off a dehumidifier and how to do it practically:

‘When Should I Turn Off My Dehumidifier’ Tips

In the summer, you can run a dehumidifier constantly 24/7, as we have pointed out in this post. Here is how to use a dehumidifier in the summer:

  1. Set a dehumidifier to 50% RH. The dehumidifier will turn itself on and run whenever its built-in humidistat measures relative humidity higher than 50% RH.
  2. At 50% RH, the dehumidifier will stop running. It will not be turned off completely; the humidistat will be on. When it records higher than 50% RH, it will start again.

In the winter, we have another set of guides. Namely, without the humidistat, we cannot determine if the humidity levels are above 50% RH or not. Here is how we should use a dehumidifier in the winter and when to shut it off:

  1. Turn off the dehumidifier yourself. In the winter, you will likely have below 50% RH humidity, so you don’t have to run a dehumidifier.
  2. Turn on the dehumidifier every 2 weeks or once per month, if you suspect you have humid air.
  3. Dehumidifier humidistat will measure the humidity levels, and act according like this: Case A) If the relative humidity is below 50%, the dehumidifier won’t start running because the moisture levels are adequate, or Case B) If the relative humidity is above 50%, the dehumidifier will start running until it reached 50% RH.

If in October and November, you experience case A (RH below 50%, dehumidifier doesn’t start), you can pretty much keep it turned off till April or even May.

If, however, you experience case B in October and November, and the dehumidifier starts running, you obviously need to keep it turned on. When the moisture levels fall even more in December and January, you can likely keep it turned off (turn it on once or twice per month just to check that you have adequate humidity levels). In March and April, you will probably need to turn it back on again since the humidity levels will increase over 50% RH again.

We hope this makes it clear when to turn off the dehumidifier. Dehumidifiers are mostly summer HVAC units that don’t need to run in the winter, but it is still smart to check from time to time (using a built-in humidistat) if you should run it in the winter as well.

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