The Silent Destroyer in Your Garage: Why Humidity is Your Enemy
I volunteered to help my friend clean out his father’s garage. He let out a sigh when he found his rusted childhood bicycle. The garage humidity was high enough for rust to set in.
It made me wonder: if there had been a dehumidifier in the garage, would his bike have survived?
A dehumidifier will absolutely work in a garage. It’s the key to stopping the silent, creeping damage caused by excess moisture.
Even a small “refrigerant-condenser” unit can reduce moisture throughout a two-car garage. For colder climates, a desiccant dehumidifier is the superior choice.
You can use the manufacturer’s “recommended square feet” to size the dehumidifier, but only if your garage has a drop ceiling. If the ceiling is exposed, there’s more air to treat. I’ll show you exactly how to calculate this to size your dehumidifier correctly.
Your Quick Guide: Choosing the Right Garage Dehumidifier
Yes, a dehumidifier will work in a garage. The trick is matching the dehumidifier type and size to your specific garage conditions.
Use our guide below to match the dehumidifier size to your garage volume. Even a small “refrigerant-condenser” unit can reduce moisture throughout a two-car garage, but this type is only effective for temperatures over 60°F.
For colder garages, you need to use a desiccant dehumidifier to get the job done right.
If you are also worried about moisture coming up through the concrete floor, a dehumidifier is a big part of the solution. Learn more in our article: Can You Really Waterproof a Garage Floor?
Why Are Dehumidifier Ratings So Confusing?
The Energy Star agency changed dehumidifier ranking requirements in 2019, causing a lot of confusion for consumers.
Where Energy Star once would have recommended a 25-pint unit, they now recommend a 12-pint machine for the same space. This is due to a change in testing conditions.
Unfortunately, not all manufacturers have adopted the new measurements, fearing it makes their products look less powerful.
A manufacturer who follows the new rules has to state “12-pint capacity,” while a competitor using the old standard can boast a “20-pint capacity,” even if the performance is identical. It’s a bit messy out there.
One way to cut through the confusion is to go by “square feet” rather than pints collected. However, this is also messy because the square foot recommendation assumes a standard 8-foot ceiling, which most garages do not have.
The Biggest Sizing Mistake: Why “Square Feet” Fails in Garages
Dehumidifier marketing often states something like “treats up to 500 sf.” The problem is, a dehumidifier doesn’t treat square feet; it treats cubic feet of air. It pulls moisture from the entire volume of your garage.
The manufacturer’s square footage recommendations assume the treated room has a standard 8 ft. ceiling. This works for most indoor rooms, but not for garages with high or vaulted ceilings.
If your garage has an 8 ft. ceiling, you can use the box’s recommended square feet. If not, you must calculate the extra air volume to avoid buying a unit that’s too small for the job.
For example, a 24 x 24 ft. indoor room has the same square footage as a 24 x 24 ft. garage, but if the garage ceiling is 16 ft. high, it contains double the volume of air. That requires a much more powerful dehumidifier.
How to Calculate Your Garage’s True Size for a Dehumidifier
Our goal is to translate your garage’s actual air volume into the “square footage” metric that manufacturers use. This simple method ensures you buy a unit powerful enough for your space.
Let’s determine what size dehumidifier is needed for a 24 x 24 x 16 ft. garage.
- Step 1: Calculate the garage volume: 24 ft. x 24 ft. x 16 ft. = 9,216 cubic feet (cf).
- Step 2: Divide by 8 to convert to “equivalent square feet”: 9,216 / 8 = 1,152 sf.
- Conclusion: You must buy a dehumidifier rated to treat at least 1,152 sf.
Think of the area above the first 8 ft. in your garage as another room stacked on top. For every additional 8 ft. of height, you have another room’s worth of air to treat.
Quick Sizing Examples for Your Garage
Here are a few quick examples to help you visualize the calculation for your own garage.
Example 1: The garage is 24 x 24 x 8.
- Calculate the garage volume: 24 x 24 x 8 = 4,608 cf.
- Divide by 8: 4,608 / 8 = 576 sf.
- Get a dehumidifier rated for a room that is at least 576 sf.
Example 2: The garage is 24 x 24 x 10.
- Calculate the garage volume: 24 x 24 x 10 = 5,760 cf.
- Divide by 8: 5,760 / 8 = 720 sf.
- Get a dehumidifier rated for a room that is at least 720 sf.
Example 3: The garage is 24 x 24 x 16.
- Calculate the garage volume: 24 x 24 x 16 = 9,216 cf.
- Divide by 8: 9,216 / 8 = 1,152 sf.
- Get a dehumidifier rated for a room that is at least 1,152 sf.
Warm vs. Cold: Which Dehumidifier Type is Right for Your Garage?
A dehumidifier will absolutely remove moisture from a garage. However, the type you need depends entirely on the temperature inside your garage.
Even a small “refrigerant-condenser” dehumidifier can reduce moisture in a two-car garage, but only if the temperature stays above 60°F.
A “desiccant” dehumidifier works in temperatures as low as 40°F. This type is most effective at removing moisture from the air immediately surrounding it, rather than pulling in damp air from across a large room.
You can get a specialized whole-room dehumidifier that works in cold weather, but according to experts at appliance manufacturers, you won’t find it in the standard household appliance section at the store.
How Dehumidifiers Work (And Why Most Fail in the Cold)
A standard household dehumidifier uses a refrigerant and a condenser, much like an air conditioner. It cools metal coils, causing moisture from the air to condense on them and drip into a collection tank.
This design relies on a temperature difference between the coils and the room’s air. As the garage air gets colder, the condenser has to get even colder to create condensation, causing it to freeze over and stop working.
As explained by home environment specialists like Stadler Form, a standard refrigerant-condenser unit loses efficiency below 60°F and is ineffective in a truly cold garage.
A desiccant dehumidifier, on the other hand, uses a chemical absorption process with a material like silica gel to pull water directly from the air. It doesn’t rely on condensation and maintains its efficiency in temperatures well below 60°F, often down to 40°F or even lower for industrial models.
What Is the Ideal Humidity for a Garage?
Excessive garage humidity fosters the growth of mold, mildew, and rust. It can also make the space feel muggy and uncomfortable, as high humidity prevents sweat from evaporating, which is your body’s natural cooling mechanism.
Getting the humidity down to about 50% creates a comfortable environment that actively discourages mold and rust growth.
If you are storing anything made of iron, steel, or paper in the garage, you must get the humidity below 60%. This is the critical threshold where moisture’s corrosive and deteriorating processes begin, according to research on corrosion prevention.
Moisture plus oxygen is the recipe for rust and corrosion. It can also cause irreparable damage to paper products over time.
Use a dehumidifier to protect your valuable tools, bicycles, classic cars, and even collections of magazines, newspapers, and books.
Where Should I Place My Garage Dehumidifier?
As long as the dehumidifier is correctly sized for your garage’s volume, you can place the unit almost anywhere it has access to the room’s air.
You will need it to be near an electrical outlet. More importantly, the machine must have clearance for proper airflow.
Manufacturers recommend giving it at least 6-12 inches of space on all sides. This means you should not place it directly against a wall.
While a specially designed wall-mounted dehumidifier is an option, a standard floor unit needs open space to breathe. Blocking its vents by pushing it against a wall will severely hinder its performance.
How to Set Up Continuous Draining
A dehumidifier collects water in a tank. Once that tank is full, the unit shuts off until you empty it. To avoid this constant chore, you can set up a continuous draining system.
You can use either gravity or a small pump to drain the dehumidifier automatically. This allows the unit to run uninterrupted, maintaining the ideal humidity level without your intervention.
For a gravity drain, simply attach a standard garden hose to the unit’s drain port. The dehumidifier must be elevated above the drainage point, such as by placing it on a sturdy table to drain water out a window.
If gravity isn’t on your side, a condensate pump is the perfect solution. Run the drain hose into a large tub or bucket, and place a small condensate pump inside. The pump will activate automatically to push the water up and out to your desired drainage location.
Ideally, the dehumidifier should run whenever humidity levels rise above 50%. You can achieve this with a unit that has a built-in humidistat, which automatically turns the machine on and off to maintain your target setting.
Another option is to use a simple plug-in timer. You can set it to run for a few hours each day and use a separate hygrometer to see if the schedule is keeping your garage’s humidity in the target 50% range.
How to Prepare Your Dehumidifier for Winter
A standard dehumidifier can break in freezing temperatures. Any water left in the pump, lines, or collection tank will expand when it freezes, potentially cracking plastic components and rendering the machine useless.
It’s not enough just to turn the unit off for the winter. You must bring the unit inside before the first freeze.
This simple act protects your investment and ensures your dehumidifier will be ready to fight moisture again next spring.
If you need year-round dehumidification in a cold garage, you must invest in a specialized desiccant model or a low-temperature refrigerant unit designed for harsh conditions.
Don’t let your cherished belongings end up like my friend’s rusted bike. Taking control of your garage’s humidity is one of the easiest and most effective ways to protect your property.
