Should A Dehumidifier Run Constantly 24/7? In Basement All The Time?

“I’ve got a new dehumidifier for the basement. Should you run a dehumidifier in the basement all the time? How many hours per day is optimal?”

This is a classic ‘how long should a dehumidifier’ run per day question. Should you run it for 8 hours? For 12 hours? Running a dehumidifier 24/7 seems a bit abnormal. But it’s actually not at all. Let’s have a look at a few things that will help you answer if you should run a dehumidifier constantly:

We all understand that high humidity is bad. This is a two-fold problem:

  • Nobody really likes high humidity in their homes. Breathing becomes harder, you sweat into your clothes, and so on.
  • High humidity causes mold growth, shortens the lifespan of furniture, rugs, and even walls.
Should A Dehumidifier Run Constantly
Dehumidifier usage only after high humidity caused wall damaged and mold growth. If we were to run a dehumidifier continuously before that (at 50% RH), the wall would be fine, and we wouldn’t see black mold growth.

That’s why the EPA specifically recommends lower humidity levels:

“Indoor relative humidity (RH) should be kept below 60 percent — ideally between 30 percent and 50 percent, if possible. Low humidity may also discourage pests (such as cockroaches) and dust mites.” (EPA on indoor humidity levels and mold growth)

Now, when you are running a dehumidifier, you are looking to get to 50% relative humidity or below. Let’s say you put a dehumidifier in a basement with 80% RH. After running it for 12 hours, the moisture levels fall to 70%. Should you now turn off the dehumidifier because you have already run it for 12 hours continuously?

Of course not. That 50% RH goal is not yet achieved. At 70% RH, you are still 20% away from ideal relative humidity levels. Mold doesn’t really care how many hours per day you run a dehumidifier; when it feels that sweet 70% RH, it will grow and cause you all kinds of problems along the way.

This is like if you had to do a 100-mile drive, but after 60 miles you would wonder if you should just park the car, and walk those remaining 40 miles.

In many cases, we are afraid that we will break the dehumidifier if we run it all the time. No worries; these units were made to handle that. What we should all be afraid of is that mold growth the EPA specifically warns about, caused by high humidity levels (not running a dehumidifier adequately).

Here is how long you should run a dehumidifier:

How Long Should A Dehumidifier Run Per Day?

Dehumidifiers are engineered to run constantly. That means they can very well run them 24/7 for weeks on end.

dehumidifier that has run constantly for weeks
Dehumidifier is a well-engineered HVAC device that can run uninterrupted for days or even weeks.

The key goal you want to achieve by running a dehumidifier is to bring the moisture levels below 50% RH. Here is how you should set your unit:

  1. Place a dehumidifier in a space with excess humidity levels. Basements, for example, are notorious for having very high 70%, 80%, and even 90% RH levels. That is why homeowners who don’t use dehumidifiers usually have a moldy smell in the basement, and green or even black mold spots.
  2. Set the dehumidifier to 50% RH. The direction you give the dehumidifier in this way is “Run constantly until you reach 50% relative humidity”.
  3. Leave the dehumidifier to run constantly, especially in the basement. It will do the job it is designed to do 24/7 if needed.
  4. When the humidity levels fall to 50%, the dehumidifier will stop running. It has done its job adequately.
  5. While the unit is not running, the RH levels can start peaking over 50% again (to 51%, 52%, and so on).
  6. When the built-in humidity sensor measures over 50% RH, it will start running again by itself. This is the Auto mode; the most useful dehumidifier setting.

Now, a lot of people ask us if running a dehumidifier continuously will shorten the lifespan of the dehumidifier. Well, yes, but that’s the point. If you have a car in a garage all the time, it will last longer, right? However, the job the car has is to drive you 200,000+ miles within 5-10 years. There is no point in having a car if you don’t use it.

Not running a dehumidifier constantly may expose you to high humidity levels. Mold, dust mites, cockroaches, wall fragmentation, sweating, heavy breathing, and a lot of other things is the cost of not running a dehumidifier 24/7.

Here is how to use the dehumidifier in the most basic terms:

Set it to 50% RH and forget it. It knows what must be done. Just be sure to empty the water bucket if your dehumidifier doesn’t have gravity draining or a pump.

If that means the dehumidifier in the basement runs all the time, that’s exactly the point of using a dehumidifier. It continuously decreases the basement relative humidity levels, and thereby protects your home.

Can You Dehumidify Too Much?

Yes. Setting a dehumidifier to 30% or even lower is a bit excessive. At 50% RH, you will stop mold growth almost entirely, and most people feel that 50% RH is quite normal.

Almost all modern dehumidifiers have built-in humidity sensors and a relative humidity setting. If you set it to 50% RH or even 40% RH, a dehumidifier will never dehumidify too much.

In short, every dehumidifier should run constantly until it reaches 50% relative humidity levels or lower. That’s what dehumidifiers are made for. What we should be afraid of is mold growth, and that will likely happen if we have high humidity levels and don’t use a dehumidifier we have on hand to remedy that problem.

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