Do Dehumidifiers Work in Garages?

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. I wondered if there had been a dehumidifier in the garage, would his bike have survived?

A dehumidifier will work in a garage. Even a small “refrigerant-condenser” unit can reduce moisture throughout a two-car garage. A desiccant dehumidifier works in colder garages.

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 will show you how to calcualte this to size your dehumidifier.

 

Save the bicycles!
Save the bicycles!

Energy Star Agency Dehumidifier Size Recommendations

The Energy Star agency changed dehumidifier ranking requirements in 2019. Where Energy Star would have recommended a 25-pint in 2019, they recommend a 12-pint machine as of 2020 and later.

Manufacturers are supposed to use the new measurements, but they fear it makes them look bad. A manufacturer who follows the rules has to say “12-pint capacity,” while the competitor doesn’t follow the rules and boasts a “20 pint capacity.” It’s a bit messy out there right now.

One way to know the dehumidifier size is to go by “square feet” rather than pints collected. This is also messy, because the square foot recommendation assumes the garage has an 8 foot ceiling. Rarely does a garage have one of these. I will show you how to calculate the dehumidifier size using your garage’s measurements below.

New dehumidifiers should use the new measuring system that you will find in the table below.

Garage Dehumidifier Size Guide (post 2019 Energy Star Dehumidifier Sizes)

Garage Size in Square Feet

500 sf.

1000 sf.

1500 sf.

2000 sf.

2500 sf.

Dampness

Minimum Dehumidifier Size

Moderately Damp (space feels damp and has musty odor only in humid weather)

10 pints

14 pints

18 pints

22 pints

26 pints

Very Damp (space always feels damp and has musty odor. Damp spots show on walls and floor.)

12 pints

17 pints

22 pints

27 pints

32 pints

Wet (space feels and smells wet. Walls or floor sweat, or seepage is present.)

14 pints

20 pints

26 pints

32 pints

38 pints

Extremely Wet (laundry drying, wet floor, high load conditions.)

16 pints

23 pints

30 pints

37 pints

44 pints

How Big Should a Garage Dehumidifier Be?

One and two car garages require dehumidifiers between 10 and 30 pints. The factors affecting the dehumidifier size include:

  • the garage temperature
  • the garage’s volume in cubic feet
  • the humidity level from “moderately” to “extremely” wet
  • whether the manufacturer is using pre-2020 or post -2020 recommendation standards

In temperatures above 60 deg. F, and using the post-2020 Energy Star dehumidifier sizes, a 10-pint dehumidifier is sufficient to treat a one-car garage that has an exposed ceiling; a 30-pint dehumidifier is sufficient to treat a two car garage with an exposed ceiling.

Manufacturers use “square feet” treated as a shortcut to help you size the dehumidifier. If your garage has a drop ceiling at 8 ft., you can use the manufacturer’s square feet to see what size machine you need to dehumidify your garage. If you have an exposed garage ceiling, you need to add in the air volume above that first 8 ft. to get the real size of the air you are dehumidifying.

Sample estimates to demonstrate sizing variables:

  1. a “moderately damp” one-car garage, insulated, with a drop ceiling, at 61 deg. F. or greater: 10-pint dehumidifier
  2. an “extremely wet” one-car garage, non-insulated, exposed ceiling, at 61 deg. F. or great: 16-pint dehumidifier
  3. a “moderately damp” two-car garage, insulated, with a drop ceiling, 61 deg. F. or greater: 14-pint dehumidifier
  4. a n “extremely wet” two-car garage, non-insulated, exposed ceiling, 61 deg. F. or greater: 30-pint dehumidifier

Are Indoor Square Feet the Same as Garage Square Feet?

The dehumidifier marketing will say something like “treats up to 500 sf.” The thing is, a dehumidifier doesn’t treat square feet of air. It treats cubic feet of air. A dehumidifier pulls  moisture from the whole volume of the garage’s air.

The manufacturer’s recommendations assume that the treated room has a ceiling at 8 ft. This caps the volume of the indoor room to length x width x 8 ft. tall. If your garage has an 8 ft ceiling, you can use the box’s recommended square feet. If not, calculate the extra volume as per the instructions below.

Compare a 24 ft. x 24 ft. Indoor Room to a 24 ft. x 24 ft. Garage

Does a 24 x 24 ft. interior room have the same amount of air as a 24 x 24 ft. garage?

  1. The interior room is 24 ft. x 24 ft. , or 576 square feet (sf.)
  2. The garage is 24 ft. x 24 ft., or 576 sf

There’s no way to know, because we don’t know the garage’s ceiling height. If the garage’s ceiling height is about 8 ft., then yes, they have about the same volume of air. You can safely get a household dehumidifier for 576 sf. for the garage.

But what if the garage ceiling is 24 ft. high? That’s 16 ft. higher than the indoor ceiling. It’s like having three 8 ft. rooms, each stacked on another. The dehumidifier is actually treating an 24 x 24 x 8 ft. room stacked on another 24 x 24 x 8 ft. room, stacked on another 24 x 24 x 8 ft. room.

  • Manufacturer recommendations are based on the room’s length times depth x height, where the assumption is that the height is 8 ft.
  • A 24 x 24 ft. garage with an 8 ft. ceiling is rare, but if you have this configuration, you can use the manufacturer’s “square feet” sizing recommendations.
  • A 24 x 24 x 8 ft. is 4,608 cf.
  • If the garage is 24 x 24 x 16 ft. high, then the garage is 24 x 24 x 16 = 9,216 cf.
  • If the garage is 24 x 24 x 24 ft. high, then the garage is 24 x 24 x 24 = 13,824 cf.

Step by Step: How to Calculate Garage Volume to Size a Dehumidifier

Our goal is to use the manufacturer’s “treats xyz square feet” to size the dehumidifier for the garage. We will calculate the garage volume, throw away the height to convert volume back to square feet, and then use that number to find the right dehumidifier size.

What size dehumidifier should we get 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 cf.
  • Step 2: Divide by 8 to work in indoor-room-height units: 9,216 / 8 = 1,152 sf
  • Conclusion: Buy a dehumidifier that treats at least 1,152 sf.

Think of the area above the first 8 ft. in your garage as if it were another room. It has 24 ft. width and 24 ft. depth, or 576 sf., but what is the garage’s height? We know that the first 8 feet of garage height is calculated into the manufacturer’s “square feet” sizing. How many other 8 ft. high rooms do we have above our first one in this garage?

For every 8 ft. above the first one, you have another room’s worth of air to treat.

If the garage ceiling is 16 ft., we have a whole 8 ft. ceiling garage space stacked on top of our first 8 ft. high room. If the garage ceiling is 24 ft., two 8 ft. rooms stacked above our first 8 ft. high room. The first room is 8 ft. The second room goes to 16 ft. The third room goes to 24 ft.

Examples Calculating Garage “Volume” to Size a Dehumidifier that Treats “Square Feet”

  • Example 1: The garage is 24 x 24 x 8. 
    1. Calculate the garage volume: 24 x 24 x 8 : 4,608 cf
    2. Divide by 8: 576 sf
    3. Get a dehumidifier for a room that is 576 sf.
  • Example 2: The garage is 24 x 24 x 10. It is 2 ft. taller than an interior room.
    1. Calculate the garage volume: 24 x 24 x 10: 5,760 cf
    2. Divide by 8: 5,760 / 8 = 720 sf.
    3. Get a dehumidifier for a room that is 720 sf.
  • Example 3: The garage is 24 x 24 x 16. It is 8 ft. taller than an interior room.
    1.    Calculate the garage volume: 24 x 24 x 16: 9,216 cf
    2. Divide by 8: 9,216 / 8 = 1,152 sf.
    3. Get a dehumidifier for a room that is 1,152 sf
  • Example 4: The garage is 24 x 24 x 20. It is 12 ft. taller than an interior room.
    1.   Calculate the garage volume: 24 x 24 x 20: 11,520 cf
    2. Divide by 8: 11,520 / 8 = 1,440 sf
    3. Get a dehumidifier for a room that is 1,440 sf

How Temperature Affects Your Garage Dehumidifier Choice

A dehumidifier will remove moisture from a garage. Even a small “refrigerant-condenser” dehumidifier can reduce moisture in a two-car garage. A “desiccant” dehumidifier works in temperatures as low as 40 deg. F. However, this type is best at cleaning nearby, and less effective at removing moisture at a distance. You can get a specialized dehumidifer that works on the whole room in cold weather, but you will not find it in the household appliances section at the store.

A refrigerant-condenser dehumidifier uses a motor to pull air in from the whole room. It is as effective  nearby as it is across the room. This dehumidifier design removes moisture in temperatures above 60 deg. F. While it might continue to operate at 60 deg. F and lower, it drastically loses efficiency as the degrees drop.

A desiccant dehumidifier uses a chemical absorption process to pull moisture out of the air. This type of dehumidifier is better at treating air nearby than air that is farther away. It removes moisture while operating in temperatures above 40 deg. F.

If you are only treating temperatures a 60 deg. F. and up, you can use a household “refrigerant-condenser” dehumidifier intended for the indoors. If you are treating a small area in temperatures 40 deg. F. and up, you can use a desiccant dehumidifier. If you are treating a large, cold area, you will need a dehumidifier modified specifically for this scenario. Manufacturers offer both refrigerant and desiccant dehumidifiers for cold, large spaces, but they are unavailable in household dehumidifier selections.

Do not allow an unfortified dehumidifier to stay outside in freezing temperatures. If you leave this type of unit outside in colder weather, it will stop working at best, and will freeze and break at worst.

All but the hardiest (modified) dehumidifiers should be brought inside before freezing weather starts. Any water left in the unit can expand and break the machine or drain.

Moisture rusts cars
Moisture rusts cars

 

Morning dew
Morning dew

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Does a Dehumidifier Work in a Cold Garage?

Moisture plus oxygen plus steel equals rust
Moisture plus oxygen plus steel equals rust

A cheapIf you bring your dehumidifier in for the colder months, a cheaper household model will work well. If you need a dehumidifier that works in cold weather in a large garage space, you will need an industrial desiccant dehumidifier, or a refrigerator-condenser unit modified to operate in cold temperatures.

 

Dehumidifiers use more energy than most appliances. To get the smallest machine that still does a good job, you need to know the garage’s size and humidity level.

Dehumidifiers intended for the indoors work with a refrigerant and condenser, and do not dehumidify cold air. You can get a specialty refrigerant-condenser unit built for colder air, or get an industrial “desiccant’ dehumidifier intended to treat cold air.

How a “Refrigerant-Condenser” Dehumidifier Works in a Cold Garage

A household dehumidifier uses a refrigerant and a condenser to cool the air next to the unit. The cooler air creates condensation. The dehumidifier removes the condensation (water) from the room.

The design depends on the temperature difference between the condenser and the room air. As the room air gets colder, the condenser has to get colder to create condensation.

A refrigerant-condenser unit reduces humidity to 50% in temperatures over 60 deg. F. A specialty version of this design will remove humidity at temperatures above 40 deg. F. As the temperature drops, so does the efficiency of the dehumidifier. Therefore, the refrigerant-condenser design does not work in a cold garage.

How a “Desiccant” Dehumidifier Works in a Cold Garage

A desiccant dehumidifier uses a silica gel that pulls water into itself. It does not use refrigerant and a condenser, and is not dependent on condensation to work.

A desiccant dehumidifier reduces humidity to 40% in temperatures over 40 deg. F. It maintains its efficiency as temperatures get colder. Specialty desiccant dehumidifiers lower humidity even at 33 deg. F.

Will a Dehumidifier Break in Freezing Temperatures?

A dehumidifier can break in freezing temperatures. Water that freezes in the pump or lines will expand, possibly to a breaking point. It’s not enough just to turn the unit off. The best action is to bring the unit inside before the first freeze.

How humid is your garage?
How humid is your garage?

What Should the Humidity Be in the Garage?

Garage humidity can cause and foster the growth of mold, mildew and rust. It can prevent people from sweating, which is the body’s natural evaporative cooling mechanism. Getting the humidity down to about 50% creates a comfortable environment that does not encourage mold or rust growth.

If you are storing iron, steel or paper in the garage, you will want to get the humidity below 60%. This is the level at which moisture’s corrosive and growth processes start. Moisture and oxygen cause rust and corrosion, and can cause paper deterioration. Use a dehumidifier to protect tools, bicycles, magazines, newspapers and books.

Water on concrete
Water on concrete

Where Should You Place the Garage Dehumidifier?

So long the dehumidifier sizes matches the garage size, you can place the unit anywhere it has access to the room’s air. You will want it to be near an electrical outlet, and the machine has to have clearance underneath, around, and on top. Give it space and electricity, and you can put it anywhere in the garage space.

Mold and mildew
Mold and mildew

Can You Put a Dehumidifier Against a Garage Wall?

Unless it is a wall-mounted dehumidifier, you should not put a dehumidifier on or next to a wall. You can mount a wall-mount dehumidifier to the wall, but do not place a floor unit against a garage wall. Wall-mounted dehumidifiers work with one end blocked. Floor dehumidifiers need clearance. You don’t want to block the machine’s access to the room’s air. Near the wall is fine, just not against it where its vents will be blocked.

How to Set a Dehumidifier to Drain

A dehumidifier collects moisture from the air and puts it in a tank as water. When the tank is full, the dehumidifier stops pulling moisture from the air. You must empty or drain the tank to continue operations.

You can use gravity or a small pump to drain the dehumidifier. When the tank drains as fast as it’s filled, the dehumidifier will continue to work without interruption.

Drain the dehumidifier using a garden hose.
Drain the dehumidifier using a garden hose.

Using gravity to drain the machine requires a garden hose and height. The dehumidifier has to be higher than the drainage point. If you wanted to drain it out a window, for example, you might put the machine on a taller table, and drain the hose through the window.

If gravity is not on your side, you can use a pump to get the water from the tank to a drainage point. Using the garden hose, direct the water into a large tub. Use a condensate pump with enough lift to overcome gravity. For example, a small Little Giant 1/30 HP pump will lift water 20 ft. Use the pump’s tube to direct the water from the tub to the drainage point.

Remove the dehumidifier water using the pump
Remove the dehumidifier water using the pump
Send an electric pump drain to the outside
Send an electric pump drain to the outside

Should You Continuously Run the Garage Dehumidifier?

Ideally, the dehumidifier should run so long as humidity levels remain above 50%. People feel comfortable between 40-60% humidity, and rust and mold start at 60% humidity. You can manually turn off a dehumidifier at desired humidity levels. You can also get an auto-sending dehumidifier that uses a humidistat to measure moisture levels. This feature allows you to set a desired humidity level, or uses a default somewhere between 40-60% humidity. Check product reviews if you intend to use this auto-sensing feature, as it is a point of common problems.

Another option is to get a timer feature. Set it to run some number of hours a day. Get a hygrometer to test if the schedule is sufficient to keep humidity levels at 50% or lower.

Rusted Bike
Rusted Bike

Sources

 

 

 

 

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