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How to Reduce Garage Workshop Humidity

In this article, I show you how to reduce garage workshop humidity to prevent tool rust and make your garage more comfortable.

Let’s face it, high humidity in a garage workshop is not a priority for most people.
Even worse, excess moisture in the air make ideal conditions for mold to grow, tools to rust, and more.
So, I show you 3 simple ways I reduced the relative humidity in my workshop.

Video Tutorial

There are many things which are difficult to explain with words and images, so be sure to checkout the video tutorial below.

Tools and Material

Below are the things I used to solve humidity problems in my garage workshop.

Introduction & Background

When I moved into my house 6 years ago, I immediately claimed the detached garage as my workshop.
The building measures 25’x25’x12′ with a 10’x10′ garage door and it contains a loft I use as a home office.

How To Reduce Garage Workshop Humidity

Unfortunately, the HVAC unit for this building was extremely old (20+ years) and never worked properly.
At first, I worked in my home office and my workshop without heating or cooling.
With spring fast approaching, I knew I had to do something soon.

After about a month without an HVAC unit, I quickly noticed my tools rusting and high humidity levels.
I planned to install a HVAC unit before spring, but I started researching ways to solve the high humidity levels.
In addition, I wanted to learn the reason for high humidity in mild temperatures.

My research led me to the topic of relative humidity. Learn more on relative humidity here.

What is Relative Humidity

Simply put, relative humidity (RH) is the amount of water vapor in the air relative to the temperature in the air.
Relative humidity (%RH) is measured as a percentage of the total amount of moisture the air can hold at a given temperature.
Absolute humidity is the measure of water vapor (moisture) regardless of temperature.

Relative humidity is as its name implies – relative.
In other words, the ideal relative humidity for my environment may be different than yours.
Ultimately, you must understand relative humidity is related to temperature.
Therefore, maintain a stable temperature and the relative humidity remains stable as well.

Acceptable Humidity Levels for Garage Workshop

I define an acceptable relative humidity level as one that prevents tool rust, mold growth, and produces a comfortable environment.
With that said, my ideal humidity level in my garage workshop is between 50% – 65%.
As I mentioned, this range may not be ideal for your environment.

3 Best Ways to Reduce Garage Workshop Humidity

Keep in mind, the 3 methods I cover in this article work in conjunction and compliment each other.
I implemented each of these 3 methods one at a time until I maintained the relative humidity between 50% to 65%.

DIY Mini Split for Garage Workshop

In order to complete this task, I used the following items.

First, I installed a ductless mini split in my large garage workshop to maintain a stable temperature in my workshop.
Obviously, I could not justify spending roughly $7,000 dollars on a professionally installed mini split, so I opted for a DIY unit.
I wrote an article on how to install a DIY mini split air conditioner and heat pump, so be sure to check that out.

DIY mini split for workshop

This mini split saved me a ton of money. Also, the performance over the past 6 years exceeded my expectations without a hit on my electric bill.

Remember, relative humidity is directly proportional to the air temperature.
So, to control humidity in a garage workshop you must control the temperature.

Additionally, an air conditioner cools air by extracting the moist warm air and injecting cool, dry air.
So, the mini split serves as a dehumidifier as long as it is properly sized for the space.
In other words, an oversized HVAC system short-cycles. This means it doesn’t run long enough to remove the humidity from the air.

Smart Mini Split Controller

Next, I installed a smart air conditioner controller in order to automate my DIY mini split air conditioning unit.

mini split smart controller

The Cielo breez plus provides me with the following benefits:

  • LCD panel to view current temperature and humidity.
  • Home Smart Controller Integration.
  • Schedules and triggers.

The video tutorial below explains how to install this unit and setup an automation to reduce humidity in my woodworking shop.

Seal and Insulate

After I installed the mini split and smart controller, I insulated and sealed my garage workshop to stop air leaks.
Although the relative humidity dropped from 80% to 70%, it was not enough to prevent tool rust and make it more comfortable.

Garage Door Insulation

First, I installed reflective paper adhered to rigid foam board panels on the interior of my garage door.
Then, I used spray foam to secure the foam panels.
It’s not pretty, but it works like a charm.
Looking back, I should have purchased the garage door insulation kit to save installation time.

garage door insulation panels

I could see sunlight coming through the bottom, sides, and top of the garage door.
So, I replaced each of these as well.
As you can see in the picture below, sunlight easily shined through the side of the garage.

garage door air leak

Workshop Wall

For some odd reason, the previous homeowner did not insulate one of the walls in the detached garage.

DIY accent wall workshop

So, I purchased wall insulation from the local big box store and installed them in the wall cavity.
In addition, I reclaimed cedar fence boards to make a DIY cedar accent wall.

Doors and Windows

Finally, I used latex plus silicone caulk to seal the windows on the interior.
I used silicone sealant for the windows and doors on the exterior.

Garage Workshop Dehumidifier


So, the mini split, smart AC controller, and a properly sealed workshop dropped my relative humidity down to 60%.
However, I needed to drop the humidity down to 50% if needed to protect my hand tools.
So, I purchased a 70-pint dehumidifier for my workshop.

garage workshop dehumidifier

This dehumidifier is a good option for humidity control.
Also, the LCD panel lets me set the desired humidity level and it simply runs until it meets the desired RH.
The panel notifies me when to clean the filter or when the bucket needs to be emptied with a blinking red light.

workshop dehumidifier setting

A removable 2 gallon bucket catches the water extracted from the moist air.
In addition, the bucket detaches easily to be emptied.

workshop dehumidifier bucket

Lastly, this workshop dehumidifier has a spigot to connect a permanent hose to drain outside instead of draining in the bucket.
I use this when I go on vacation or leave for more than a few days.

workshop dehumidifier with drain connection

Final Results and Conclusion

The DIY mini split, a properly insulated garage workshop, and a dehumidifier solved my high humidity problems.
Furthermore, I can now easily reduce the relative humidity in my workshop down to 40%.
I hope you learned how to reduce garage workshop humidity and this article saves you time and money.

Frequently Asked Questions

What size dehumidifier do I need for a garage workshop?

Each dehumidifier is rated to cover a square footage amount, so it depends on the size. Usually, a 70-pint dehumidifier is adequate for most garage workshops.

Why is relative humidity more important than absolute humidity?

Relative humidity is more important than absolute humidity because it takes into account air temperature. It also measures the air’s ability to hold water.

How do I prevent mold in my garage?

To prevent mold in a garage, you should seal, insulate, and install a HVAC system such as a mini split.

Are mini splits good for a garage or workshop?

Mini splits are ideal for garages because they are energy efficient, and require no duct work. DIY mini splits are available and cheaper than a professionally installed unit.