Dehumidifier Size Calculator

Don’t purchase your dehumidifiers as though they’re grocery items. See one that seems large, look up the cost, and think: “I’ll get that one.” That never goes well. It’s not because these things don’t work. It’s because you’ve got the wrong size. It runs all day and burns power, but fails to remove much water from air.

Finding the right capacity take into account all sources of moisture in the room. There’s more math involved then there is gut feeling. To do this, we have a calculator (above) that will crunch all of the numbers for you after entering size of your room and relative humidity levels that you want to maintain. This begins with information like your room’s height, width, and length.

How to Choose the Right Dehumidifier

While it may seem like it should simply be based off your floor space, the reality is that it’s constrained by volume. The reality is that it is limited by volume. The air volume contained in a room with ten foot ceilings are much larger than a room with eight foot ceilings, even if they are both the same size on the ground. That means there’s so much more air that needs to be dehumidified down to your desired level before machine will begin to maintain that level.

Next: How much moisture are you trying to dry? That’s the part of most estimates people get wrong. They don’t realy understand the source of all that moisture. Are there wet spots on concrete? Is it mostly air replacement? Do you have laundry drying inside? All these factors help determine amount of moisture load per day. You will rate this on a scale, and the tool translate your rating into a daily moisture load factor.

If you’ve got a slightly damp room, you’ll want a small unit; if your space requires regular outside air exchange or has actual seepage, then the required capacity are much higher. If you undersize your unit, it will simply be cycling on and off without ever reducing the humidity.

The second big variable is relative humidity. Drying out what’s already in there is only part of the story. That air is being replaced by more from outside which often happens via cracks in your foundation, windows and doors. That’s where the air-change factor comes into play. While a tight bedroom may see its air exchanged a few times a day, a drafty basement could experience dozens. And each time fresh moist air comes in so does another job for the dehumidifier. Underestimate the leakage, and the unit will be working forever without ever catching up to the load.

What it produces is your suggested capacity class in pints per day. That’s what we call these standard buckets of capacity, matching existing products on the market. You’ll find everything from super-hi-load machines for heavy-wet applications to more compact units for smaller spaces like closet.

There’s a reserve margin built into the calculation. That’s a safety buffer so the system won’t be running full-out all the time. Running full-out cuts its efficiency and shortens its lifespan. Usually a good bet is to round-up to the next capacity class.

Then there’s placement. Even with the proper size, putting your dehumidifier in a corner or tucking it behind a piece of furnitures is meaningless; air must be able to flow through it. Airflow is how a dehumidifier functions. It takes in moist air, removes the water by condensing it, then blows dry air back into the room. Limiting its airflow means the sensor reads the correct humidity level near the unit but the remaining area remain humid. Keep it in an open area with at least several feet of space on all sides.

Last but not least: Keep in mind that a dehumidifier is a band-aid, not a solution. No amount of drying out will solve the root cause if your basement has serious structural leaks or standing water. The machine will handle what’s already there, but won’t prevent more water from coming in. Use the tool to determine proper size for your load and check the outcome. If the machine runs continuously at the correct size yet the humidity persists, this points toward a structural (rather than mechanical) problem.

Get the size right, make sure the air is circulating, and allow the machine to perform its function. You would of wanted a comfortable, dry space, not a machine that never sleeps.