A dehumidifier is a device that is placed in a room in the house to remove excess moisture from the air. The right size of the dehumidifier is important to ensure the equipment is working effectively in the room or area. For example, a large area with high humidity may require several dehumidifiers or one large dehumidifier; whereas small bathrooms only need one small dehumidifier. Read on to find out how to choose the right dehumidifier for your needs.
Step
Step 1. Use a hygrometer to get an accurate measure of the humidity of a room or area
Hygrometers can be purchased at retail stores that specialize in home improvement and will give you the percentage of humidity present in a given area or room
Step 2. Use the specific characteristics of the room to determine the humidity level if you don't have a hygrometer
- If the room is very wet and has puddles or pools of water, the humidity will be between 90-100 percent and is considered “very wet”.
- If the room smells and feels damp, and has mold, mildew, leaks, and water spots, the humidity is between 80-90 percent and is classified as “wet”.
- If the room feels very damp and you can clearly smell mildew, the humidity is between 70-80 percent and is considered “very damp”. There may be water spots on the walls or floor.
- If the room only smells musty in damp or wet weather, the relative humidity is between 60-70 percent and is considered “moderately humid.”
Step 3. Determine the Air Change per Hour (ACH) to calculate the airflow required to properly remove the humidity in the room
- If the humidity is “very wet” or between 90-100 percent, the ACH will be “6”.
- If the humidity is at the “wet” level, or between 80-90 percent, the ACH will be “5”.
- When the humidity in the room is “very humid” or between 70-80 percent, the ACH will be “4”.
- Humidity in a "moderate" room, aka between 60-70 percent, will have an ACH value of "3".
Step 4. Calculate the area of the room or area that needs to be reduced humidity
- Measure the length and width of the room using a ruler or measuring tape.
- Multiply the length and width of the room to find out how large it is.
- For example, if a room is 3 meters long and 4 meters wide, the area is 12 square meters.
Step 5. Calculate the volume of the room from which the moisture will be removed
The trick is to multiply the area of the room by its height.
For example, if the area of the room is 12 square meters, and the height is 5 meters, it means that the volume of the room is 60 cubic meters (5 meters x 12 square meters)
Step 6. Determine the amount of air flow or cubic feet per minute (CFM) required to remove humidity using room volume and ACH
- Multiply the volume of the room by ACH, and divide the result by 60.
- For example, if the volume of the room is 60 meters, and the room is considered "very wet", multiply 60 by 6 to get 360. Divide 360 by 60 to get the required amount of airflow, which is 6 cubic meters per minute.
Step 7. Determine the pints of humidity that need to be taken each day to remove moisture from the room
- For moderate humidity conditions, you will need a dehumidifier that can take 5 liters of water from a 45 square meter room. For every additional 45 square meters, add 2 liters. For example, for a room of 140 square meters, you need a dehumidifier capable of taking 8.5 liters of water.
- For very humid conditions, buy a dehumidifier that can take 6 liters of water from a 45 square meter room. For every additional 45 square meters, add 2.5 liters.
- For wet conditions, choose a dehumidifier capable of taking 6.5 liters of water from 4.5 square meters. Add 3 liters for every additional 4.5 meters.
- For very wet conditions, buy a dehumidifier capable of taking 7.5 liters of water from 45 square meters. Add 3.5 liters of water for every additional 45 square meters).
Step 8. Purchase a dehumidifier that can meet both CFM and pint requirements
- Read the dehumidifier manufacturer's label and packaging to determine the correct size.
- If the CFM level is significantly higher than the CFM level the dehumidifier supports on the package, you may need to purchase some equipment for the room concerned.
- If the CFM levels are in the CFM range that the dehumidifier supports, we recommend purchasing a unit with a higher CFM than required, and reducing the frequency of use.
