As we have talked about in this post, you can run a dehumidifier constantly 24/7. However, at certain hours of the day, the dehumidifier is more effective (and useful) than at others. Let’s look at what is the best time of day to use the dehumidifier most effectively.
Namely, these 2 key factors play a role in what are the best hours of the day to use a dehumidifier effectively:
- Dehumidifier is most effective during the ‘humid hours’. At high humidity (70%, 80%, even 90% RH), a 30-pint dehumidifier can be as effective as a 50-pint dehumidifier at 60% humidity. The time of day when we see the highest humidity is during the night and in the early morning (we’ll explain why).
- Electricity rates. Dehumidifiers run on electricity. In this post, we see that a 30-pint dehumidifier runs on about 300 watts. That’s 0.3 kWh per hour. Here we can take advantage of the cheaper off-peak electricity rates (usually between 10 PM and 8 AM). Example: At peak electricity rates (let’s say $0.25/kWh), we will pay about 8 US cents/h to run a 30-pint dehumidifier. If the rates fall to $0.15/kWh in off-peak times during 10 PM and 8 AM, we are now paying about 5 US cents/h; a 40% reduction in dehumidifier running cost.
Now, it makes sense to use a dehumidifier in that part of the day when the humidity is the highest and when the electricity rates are the lowest.
We already know that we will pay less for electricity during off-peak hours (10 PM and 8 AM). Let’s now have a look at why the dehumidifier efficiency is the highest during the night and morning (and why it would be a mistake to run it in the afternoon):
How To Use Dehumidifier Effectively During The Day
Here is what National Weather Service says about when the humidity levels are the highest:
“The relative humidity will be highest in the early morning when the air temperature is coolest, and lowest in the afternoon when the air temperature is highest.” (weather.gov on daily humidity levels)
We can see that relative humidity is closely connected with temperature. This has to do with water dew point and how we measure relative humidity (due to this temperature effect, we call it “relative” humidity in the first place).
At low temperatures (night and morning hours), we will have high humidity (let’s say 70% RH). At higher temperatures (noon and afternoon), we will have low humidity (let’s say 55% RH or even 50% RH).
Since the purpose of a dehumidifier is to decrease relative humidity (ideally to 30% to 50% RH), it will be most useful when the humidity is the highest. The hours of the day that humidity is the highest quite nicely follows that 10 AM to 8 AM daily time window.
That’s why the best time of day to use a dehumidifier is between 10 PM in the evening and 8 AM in the morning.
Within these hours of the day, we have this perfect triplet of factors that make running the dehumidifier effectively:
- Relative humidity is the highest.
- Dehumidifier dehumidification rate is the highest (since the humidity is the highest).
- Electricity is the cheapest.
All these 3 factors add to the efficiency of using a dehumidifier. So, if you want to get the most out of your dehumidifier, run it during the night and in the early morning. Another thing you should also look into is getting the most energy-efficient dehumidifier you can get your hands on; here is a list of the most efficient dehumidifiers that will help you out.
You presume that electricity costs less at night. While I agree it cost less for the utility to generate power at night, I don’t believe most customers have time of use electric meters. Thus they pay an average cost for electricity for both kWh and kW.
Hi Tim, I get you, there is some merit to this, you are right. Nonetheless, the highest daily humidity levels are during the night and early morning; even without the cheaper electricity rates, it still makes sense to run a dehumidifier during early morning hours, for example.