Dehumidifiers – Everything You Wanted To Know About Dehumidification


Dehumidifiers – Everything About Dehumidification

Q) What does a dehumidifier do?dehumidifier selection guide

A) A dehumidifier takes moisture out of the air by sucking in moist air on one side, moving that air over some ice cold tubes that causes the moisture to collect on these tubes and then drip into a bucket or tube, and pushing the dry air out the other. This dry air then mixes with the moist air making it a little drier, which in turn is pulled into the unit to become drier over and over again.

Q) What size dehumidifier do I need?

A) Sizing Rule of Thumb for most areas except coastal is:
Up to 400 square feet: 25 or 30 pint
Up to 800 square feet: 40 pint
Up to 1000 square feet: 50 pint
Up to 1300 square feet: 65 pint

  • For coastal areas the square foot coverage will be reduced as much as 50%.
  • All of these figures are based on an 8’ high ceiling. So if the height is 10’, then add 25% more to the square footage and if 12’ high, then add 50%, etc.

Q) How much will my dehumidifier be able to lower the humidity?

A) That will depend on a lot of things. Most importantly, the temperature in your room will determine the minimum humidity level you will be able to achieve. With most dehumidifiers the air comes out at around 30% humidity. At 70 degrees and higher it is possible to reduce the humidity to 35% to 40%. As the temperature goes below 70 degrees and down into the 50’s this will rise to 60 %. If the humidity reached is not as low as you want, you can heat the room or raise the dehumidifier off the floor where it is coldest. Since heat rises the air temperature will be higher as you elevate it towards the ceiling.

This will enable you to further lower the humidity. There are other factors affecting how low you can bring the humidity level, such as the size of the area you are dehumidifying, construction of the room, and the area of the country where you live.

Q) What do you mean by 30 pint, 50 pint, or 65 pint dehumidifiers?

A) That number tells you approximately how many pints on water it can remove in 24 hours.

Q) What is a low temperature dehumidifier?

A) It is designed to operate at temperatures below 65 degrees. If the temperature drops to 65 degrees or below, the water will freeze on the condenser coils in the dehumidifier and either heat up and shorten it’s life, or cause it to cycle on and off as the water melts and quickly freezes without removing any moisture from the air. (Note – the Danby low- temp dehumidifiers and our Frigidaire low temp dehumidifiers are our top rated low temperature home dehumidifiers).

Frigidaire FFAD7033R1 70 Pint Dehumidifier
Frigidaire 70-pint Low Temperature Dehumidifier

Q) How do I know what the humidity level is in the area I want to dehumidify?

A) You can use a hygrometer to measure the humidity. It is like a thermometer, but reads humidity levels and not temperature levels. We offer a combination digital hygrometer and thermometer for measuring the humidity in your home and basement.

Q) At what humidity level should I keep the room?

A) We recommend 50% or just below because mold will not grow below 50%.

Q) What happens if I try to keep the room at 40% or 35%?

A) You will be wasting money on electricity. And you usually cannot dehumidify much below 40%.

Q) What is an adjustable humidistat?

A) A dial or digital input that allows you to set the machine to dry the air to the level you choose.

Q) What happens if I buy too small a unit?

A) The unit will operate continuously and probably not dehumidify down to 50% to prevent mold.

Q) Won’t it still make the room feel more comfortable?

A) Yes, but it won’t prevent mold from growing because the humidity may stay above 50%?

Q) Will I be wasting money if I buy too large a dehumidifier?

A) Not necessarily. The unit will shut off more quickly which can save you electricity and it gives you a margin of safety.

Q) How much will it cost to run?

A) It depends on how much moisture you need to remove and how long it needs to run to achieve your desired level?

Q) Should I turn off the dehumidifier in the winter?

A) If you want, but if you do leave it on it will work whenever the humidity rises should there be a leaky pipe or a quick thaw of the snow outside.

Q) How large is the water collection bucket?

A) Usually between 15 and 20 pints regardless of the capability of the unit.

Q) How often will I have to empty the bucket?

A) That depends on how much moisture you have in the room and how low you want to dehumidify.

Gray Aprilaire 1850F 95 Pint Dehumidifier
Aprilaire 1850F 95 Pint Portable Basement Dehumidifier

Q) Does that mean that if I have a 65 pint unit with a 20 pint water bucket, that I will have to empty it more than once a day?

A) Yes, if you have that much moisture in the room.
But you won’t have to empty at all if you set up constant drainage using gravity or an auxiliary pump.

Q) Can the bucket overflow?

A) No. Almost every unit has a float switch to shut off the unit when the water rises to a certain level.

Q) How will air conditioning affect the dehumidifier?

A) If the area that you want to dehumidify has air conditioning, then it will almost double the coverage of the dehumidifier.

Q) Can I mount this in the wall between 2 rooms?

A) Yes. It may not be as efficient as if it were in the same room. If you mount the dehumidifier in a wall, the moist air is pulled from one room and the dry air is pushed into the other, so you will have to leave the doors open between the rooms for air circulation or have a large gap under the door.

Q) Can I place the dehumidifier in a cabinet?

A) No. Some units produce a fair amount of heat that could cause a problem, and they need maximum airflow around them.

Q) How much heat do they produce?

A) It is partly a function of how long the unit needs to run to achieve a humidity level you want to attain.

In a large room or basement might be 3 or 4 degrees, but in a small room or a closet it could raise the temperature by 3-8 degrees.

Q) Won’t that heat make my air conditioner work harder and longer?

A) No. It is easier to cool or heat dry air than air with moisture and so the air conditioner will work less.

Q) Can I have windows open while I dehumidify?

A) No, or you will be trying to dry the air outside of your house.

Q) If I leave the cellar door open will it dehumidify the upstairs?

A) Only an insignificant amount. Better to leave it closed.
Also, if you have the windows open you will be trying to dehumidify the outdoors in addition to the upstairs. Therefore, it is recommended to keep the cellar door closed.

Q) Can I use an air purifier at the same time I’m using the dehumidifier in the room?

A) Yes, an air purifier will not affect the performance of a dehumidifier.

Q) Does a dehumidifier cool the room?

A) No, it actually adds heat, but it will feel much more pleasant because the air is drier.

Q) Which side is the bucket on? Or which side does the air come out?

A) The bucket will be on the side where the air is pulled in. Drawing from the front means front bucket.
(Note: Our Frigidaire and Danby dehumidifiers have front buckets with carry handles; the Winix have a rear bucket.)

Q) Do I need to place the dehumidifier in the center of the room?

A) Placement does not have to be in the center of a room, but placing it near the middle would be helpful. Since humidity will equalize itself in an air space it is not absolutely necessary for it to be located in the middle of the room.

Q) Can I dehumidify more than 1 room?

A) No, if the connecting doors are shut.
Yes, but not as well as a unit in each room. The room in which the unit is placed will become the driest. The dehumidification process can be helped by using a small fan to move the air out of the back of these satellite rooms.

Pure & Dry 70 Pint HEPA Air Purifier Dehumidifier

Q) Does the dehumidifier filter help clean the air that I breathe?

A) Not really. The filter is used to prevent dust from getting on the cold coils and reducing efficiency. Though there are some dehumidifiers that are also air purifiers like the Pure & Dry.

Q) How often should the filter be cleaned?

A) Check it monthly in the beginning to find out how often it needs to be cleaned and then clean accordingly.

Q) How do I clean the filter?

A) Remove it according to the instruction manual, and then wash it under faucet using low pressure or rinse it out in the sink. Try to wash the particles back out instead of forcing them through the filter.

Q) What can happen if I don’t wash the filter?

A) The clogged filter will restrict the airflow and reduce the efficiency and could cause it to overheat which will shorten the working life of the unit.

Q) What about a large basement or commercial area for dehumidifying?

A) We recommend the Aprilaire 1850F Basement Dehumidifier. Both are excellent dehumidifiers that can remove up to 110 pints/day for up to 2500 sq. ft with a drain tube to remove the water. A pump is optional as is a duct kit to allow ducting into multiple rooms. This ducting from room to room can be as simple as dryer hose or PVC pipe. It can be used freestanding, or add ducting to it to duct into multiple rooms, or be tied into a central air/ heating system’s ducting. has an extensive range of residential and commercial dehumidifiers and a great deal of information about each model we offer or call our dehumidifier experts at 1-888-236-7231 to discuss your needs. 


  • matt

    Is there a certain amount of time i should leave the dehumidifier to drain out after being switched off?


  • Do you mean after you are done using it? Or after the dehumidifier automatically shuts off because it is full of water? Either way, if the bucket is empty and you have the drain hose attached it should dry out within 24-48 hours.

  • New user

    First time user. I have a 70 pint for an approx. 600 plus size room. Larger than needed for what I consider to be a low level mold problem which we had cleaned. The instructions for my unit says to leave it on continuous setting for at least 3-4 days. Should I lessen that time for having a larger unit? The room feels warm. I cant say were breathing better because its warm.

    Also since dehumidifiers is supposed to take the moisture out of a room does this mean I should close the door to the adjacent half bath where the toilet is filled with water and also get rid of the fish aquarium?

  • Yes, let it run on continuous setting for 3 days. You can keep an eye on the humidity level of the room and if it is at your desired level (40-50% relative humidity) you could turn it to automatic setting where it would maintain the set humidity level. Though the toilet and aquarium water will evaporate into the air, the amount of additional moisture those are adding is so minimal they will not cause a moisture problem (unless you have a huge aquarium). If the dehumidifier is appropriately sized to the area it is dehumidifying, you should soon no longer be at risk for mold growth. If you continue to see mold growth check for water leaks and find the source of the excess moisture.