How to Build a Wood Drying Kiln: The Ultimate DIY Guide
Wood drying kilns are a great way to dry lumber since they save us from waiting months or years for the lumber to air dry.
However, drying lumber in a commercial kiln can be expensive. Also, there may be times it is just unpractical or unavailable to use a commercial kiln.
That’s why many woodworkers build their own wood-drying kilns. If you’re interested in building your own wood-drying kiln, this post is for you.
We’ll go over everything you need to know about building a DIY wood drying kiln, including:
So, if you’re ready to learn how you can dry lumber with your very own wood-drying kiln, let’s get started!
Before we delve into the nitty-gritty of building a wood-drying kiln, I want to mention that there are different types of kilns you can build.
A lot of things we’ll be talking about will depend on the type of wood-drying kiln you want to build.
Certain aspects we will cover may not be available in commercial kilns. This is a DIY guide, after all.
Our goal is to build a wood drying kiln that will give you the most control over the drying process.
While doing that, we want to build a kiln that is relatively easy and inexpensive to construct. Needless to say, we also want our kiln uses the least amount of energy while still getting the job done efficiently.
So, with that in mind, let’s go over the different types of wood-drying kilns!
Kiln Project #1 (Traditional Kiln)
Required Materials
Construction Steps
1. Build the frame
Building the frame is probably the most challenging part of this project. You’ll need to cut and nail/screw together a bunch of lumber to create a box. This will be the shell of your kiln.
Make sure the frame is square and level before you move on. If you want, you can add some exterior siding to the kiln at this point. This is optional but it will make your kiln look nicer and last longer.
You’ll need to cut a door into the side of the frame. This will be where you load and unload lumber. The size of the door will depend on how much lumber you want to be able to dry at one time.
A good rule of thumb is to make the door about one-third the width of the frame. So, if your frame is six feet wide, make the door two feet wide.
Once the door is cut out, you’ll need to build a way to suspend the lumber off the ground inside the kiln. If you don’t have any racks, you can just nail some scrap lumber to the inside of the frame to create a makeshift rack.
Just make sure there’s enough space between the bottom of the lumber and the ground so air can circulate around it. Now that the frame is built, it’s time to insulate it.
2. Insulate the frame
When it comes to insulation, you have a few different options. You can use a rigid foam board, fiberglass board, or any other type of rigid insulation that will fit inside your frame.
Avoid using loose-fill insulation like fiberglass batting. It will make it harder to seal the kiln later on. We recommend using at least R-12 insulation but the higher the R-value, the better.
Once you’ve chosen your insulation, cut it to fit inside the frame and staple or nail it into place. Make sure there are no gaps around the edges of the insulation.
If you want, you can add a vapor barrier to the inside of the frame before you install the insulation. This is optional but it will help prevent moisture from getting into the insulation.
3. Seal the frame
Use a high temp caulk or sealant to seal up any gaps around the door and seams in the insulation. You can also use construction adhesive to attach the insulation to the frame. This is optional but it will help hold the insulation in place.
4. Install the dehumidifier, space heater, and box fan
Now it’s time to install the dehumidifier, space heater, and box fan. These are the three main components of the kiln. Start by putting the dehumidifier in the kiln.
In order to use these devices, you’ll need to drill some holes in the frame for the cords. Make sure the cords are long enough to reach an outlet. Also, make sure the holes aren’t big enough that they will let heat escape.
To prevent heat from escaping, and better manage cable cords, you might want to install a cable organizer at this stage. It will help you keep the cords tidy and organized, as well as seal up any gaps around them.
You will also need to leave a hole in the top of the frame for the exhaust hose of the dehumidifier. This is where the humid air will be expelled to the outside.
After the dehumidifier is installed, put the space heater in the kiln. This will be used to control the temperature inside the kiln. Space heaters come in a variety of sizes so choose one that’s appropriate for the size of your kiln.
Next, install the box fan. This will be used to circulate air inside the kiln. The fan should be mounted near the top of the frame so it’s pointing down into the kiln.
The reason for this is that hot air rises and you want the fan to mix the hot air with the cooler air near the ground. This will help evenly dry the lumber.
Now that the main components are installed, you’ll need to wire them all together. First, connect the dehumidifier to an outlet. Then, connect the space heater to the dehumidifier.
The box fan should be connected to the space heater. This will allow the fan to turn on and off with the space heater. If you want, you can also wire the fan to a switch so you can control it independently.
5. Install the monitoring equipment
The last step is to install the monitoring equipment. This includes a thermometer and humidity sensor. These sensors will help you monitor the temperature and humidity, levels inside the kiln.
You can find these sensors at most hardware stores. We recommend getting a digital sensor so you can easily read the readings. They usually come with a display that you can mount on the outside of the kiln.
The sensors should be mounted near the center of the kiln but not directly around the space heater or box fan.
This is because the air near these devices will be artificially cooled or heated and it won’t give you an accurate reading of the overall temperature inside the kiln.
6. Calibrate the kiln
Once everything is installed, you need to calibrate the kiln. This means setting the temperature and humidity levels to what you want them to be.
To do this, you’ll need to adjust the settings on the space heater and dehumidifier. Start by setting the space heater to the desired temperature.
Then, set the dehumidifier to the desired humidity level. The humidistat on the dehumidifier will likely have a range of 30-60%.
You can also adjust the fan speed to control the circulation of air inside the kiln. A higher fan speed will circulate more air but it will also use more energy.
It’s a good idea to start with a lower fan speed and increase it if you find that the lumber isn’t drying evenly.
Once the kiln is calibrated, you can start drying lumber! We recommend starting with smaller pieces of lumber and gradually working your way up to larger pieces.
This will help you get a feel for how the kiln works and how long it takes to dry lumber.
It is important to mention that your first few batches might not be perfect. That’s normal! Since your frame is also built by the lumber you are drying, it will take a few batches to get everything working perfectly.
Kiln Project #2 (Vacuum Kiln)
A vacuum kiln is a type of kiln that uses a vacuum to remove the air from the drying chamber.
This allows the lumber to dry faster and more evenly. A vacuum kiln is a bit more complicated to build than a standard kiln but it’s well worth the effort.
Required Materials
For this project, we want to use a stainless steel vessel. This is because it has a higher chance of being airtight than other materials. However, if you believe that another material will work better for your project, feel free to use it.
The goal is to create a chamber that is as airtight as possible. This will allow you to create a vacuum inside the chamber and remove the air from the lumber.
You will also need a pump to create the vacuum. You can use a standard vacuum pump or an air compressor.
If you use an air compressor, you will need to have a way to regulate the airflow. This can be done with a valve or by using different size hoses.
Let’s take a look at how to build a vacuum kiln.
Construction Steps
Building a vacuum kiln is similar to building a standard kiln. The biggest difference is that you need to create an airtight chamber. With standard kilns, some air will always leak in and this is not a problem.
However, with a vacuum kiln, even a small amount of air leakage can ruin the drying process.
Because a vacuum kiln removes the air from the chamber, any air that leaks in will replace the air that was removed.
The first step is to build a frame for the chamber. Although this is a DIY project, building a vacuum kiln is not as simple as building a standard kiln.
You will need professional tools and materials to build a chamber that is airtight.
1. Build the chamber
The first step is to build the chamber. This is where you will place the lumber to be dried. The chamber will be a stainless steel vessel because it is more likely to be airtight than other materials.
The chamber needs to be large enough to hold the lumber you want to dry. It also needs to be tall enough so that the lumber can be placed in a horizontal position. Building a vessel is not a simple task and it is beyond the scope of this post.
If you are not confident in your ability to build a chamber, we recommend that you purchase one. The chamber should have a lid that is airtight when closed. The lid will need to have a hole for the hose.
The chamber also needs to have a way to attach the pump. This can be done with a threaded fitting or by welding. Once the chamber is built, it needs to be tested for leaks.
2. Attach the pump
The next step is to attach the pump. This can be done with a threaded fitting or by welding.
If you are using an air compressor, you will need to have a way to regulate the airflow. This can be done with a valve or by using different size hoses.
Once the pump is attached, you need to test the chamber for leaks. If there are any leaks, they need to be fixed before moving on to the next step.
Now that the chamber is built and the pump is attached, you can move on to the next step.
3. Attach the valves
The next step is to attach the valves. This will allow you to control the flow of air into and out of the chamber. You will need two valves; one for the inlet and one for the outlet.
The inlet valve is used to control the flow of air into the chamber. The outlet valve is used to control the flow of air out of the chamber. Both valves need to be able to seal the chamber completely.
Once the valves are attached, you need to test the chamber for leaks. If there are any leaks, they need to be fixed before moving on to the next step.
4. Install Gauges
Gauges are inexpensive instruments that make it possible to monitor the process. You will need two gauges; one for the vacuum and one for the pressure.
By monitoring the vacuum, you will be able to tell if the chamber is sealed. If the vacuum drops, it means that air is leaking into the chamber. By monitoring the pressure, you will be able to tell if the pump is working properly.
5. Install Filters
Filters are not required but we recommend that you install them. Filters will help to keep the chamber clean and free of dust. You can use any type of filter that you like.
The most important thing is to make sure that the filters are installed in a way that they will not leak or significantly reduce the airflow. Needless to say, you need to clean or replace the filters regularly.
6. Finalize electrical connections
The next step is to finalize the electrical connections. This will allow you to power the pump and the valves. The first thing you need to do is connect the power supply to the pump.
If your valves open and close automatically, you will also need to connect the power supply to the valves. If your valves are manual, you will not need to do this.
After the power supply is connected, you need to connect the hose to the chamber. The hose needs to be airtight so that no air can leak out.
Kiln Project #3 (Solar Kiln)
A solar kiln is a kiln that uses the sun’s energy to dry lumber. Solar kilns are simple to build and they are very efficient.
Since they rely on the sun for power, they are very inexpensive to operate.
Building a solar kiln is a great project for anyone who wants to dry lumber without using electricity. They dry wood faster than air-drying but they aren’t as good as traditional kilns that use electricity.
Required Materials
Construction Steps
The first step is to find a location for the kiln. The kiln should be located in an area that gets full sun for most of the day.
The kiln should also be located near a power outlet so that you can plug in the fan (if you are using one).
1. Build the frame
The frame will be the carcass of the kiln. It will be made out of lumber and it will be covered with clear corrugated plastic. The frame should be big enough to hold the amount of lumber that you want to dry.
To build the frame, start by cutting the lumber to size. Cut two pieces for the sides, two pieces for the front and back, and two pieces for the top and bottom. Nail or screw the frame together.
2. Cover the frame with insulation board
The next step is to cover the frame with an insulation board. This will help to keep the heat in the kiln.
Cut the insulation board to size and attach it to the frame with nails or screws.
Be sure to seal any gaps around the edges of the insulation board so that no heat escapes. You can use caulking or spray foam to seal the gaps. By sealing the gaps, you will make the kiln more efficient and it will dry the lumber faster.
3. Place the tar paper on the frame
Tar paper is intended to intensify the sun’s heat. Place the tar paper on all exposed surfaces of the insulation board except the top. On the top, you will place the clear corrugated plastic.
Attach the tar paper to the frame with staples or nails. Check that the connection is going through all of the layers that have been placed on the frame.
4. Connect the clear corrugated plastic
The next step is to connect the clear corrugated plastic. This will allow the sun’s heat to enter the kiln. Cut the plastic to size and attach it to the frame with staples or nails.
Make sure that the plastic is sealed around the edges so that no heat escapes. You can use clear packing tape to seal the edges of the plastic. Be sure to seal all of the edges so that the kiln is airtight.
5. Install the fan (optional)
The next step is to install the fan. The fan will help to circulate the air inside the kiln. It is an optional step but it will enhance the efficiency of the kiln by circulating the air.
A better-circulated air will help the lumber to dry faster providing a more uniform drying. The fan will also help to cool the lumber so that it doesn’t warp or crack.
To install the fan, cut a hole in the top of the kiln. The hole should be big enough to fit the fan. Attach the fan to the hole with screws or bolts. Be sure to seal around the edges of the fan so that no heat escapes.
You can use clear packing tape or caulking to seal the edges. Finally, connect the fan to the power outlet.
