Build Your Own Wood-Drying Kiln: A Complete Guide

When it comes to drying wood, using a kiln is the fastest, most common, and most convenient way to do it.

Often, woodworkers will find someone with a kiln and hire them to dry their wood. Those with fairly large businesses may even have purchased their own from kiln manufacturers.

However, did you know that you can build your own wood-drying kiln? If you have a smaller operation or are just getting started in your woodworking business, building your own kiln might be the best place to start.

If that sounds like you, keep reading. You’ll learn:

• The different types of small-scale wood-drying kilns
• How to pick the right one for you
• How to build your own kiln
• A key part of kiln drying your own wood

Let’s get started.

What are the different types of small-scale wood kilns?

There are several types of wood-drying kiln designs with varying features, but in this article, we’ll talk about three types:

1. Solar kilns
2. Dehumidification kilns
3. Shed kilns

Let’s get a brief overview of each type and how they work.

Solar kilns

As the name suggests, solar kilns use the energy—read heat—from the sun to dry wood. And because the sun is free and hot, solar-drying kilns are relatively simple, cheap, and safe.

Because you are using heat from the sun and not from a heater, the heat is much less intense, leaving a bigger margin for error when it comes to overdrying.

A solar kiln works by collecting heat from the sun, which shines its light through the roof and onto a collector for solar energy. The inside of the kiln is often painted black to absorb the heat, which is then circulated throughout the kiln by fans. When humidity collects within the kiln, it’s vented.¹

According to the United States Department of Agriculture Forest Service (USDAFS), with one month of moderately sunny weather, you can dry a good amount of wood (the solar kiln they were referencing can dry up to 800 board feet of 1-inch thick lumber).²

Dehumidification kilns

If you’re new to kiln building, a dehumidification kiln might be a great start. A research article by the USDAFS shares that woodworkers, even those with “a limited knowledge of kilns,” can experience the benefits of building and using dehumidification kilns.³

Unlike solar kilns, they don’t require sunny days to run. So, they are less dependent on external conditions.⁴

This type of wood-drying kiln functions exactly as it sounds: it dries wood using a dehumidifier. Here is how the USDAFS describes the process:

A commercial stand-alone dehumidifier is placed in the kiln (drying chamber). This dehumidifier works like an air conditioner except the dehumidifier has both its hot and cold coils in one unit. A fan draws the warm moist air into the unit and the moisture condenses on the cold coils that are similar to an air conditioner’s evaporator coils. The condensation drips through a hose to a drain or into a removable bucket (Fig. 3). The second set of coils warms the cool dry air, and the warm, dry (reconditioned) air is pumped into the kiln to absorb more moisture from the lumber.⁵

Overall, a small dehumidification kiln is an economical and efficient option that isn’t dependent on the weather.

Shed kilns

Shed kilns are an inexpensive option, making them great for woodworkers who are just getting started in their businesses.

Shed kilns mimic air drying—but with greater airflow and more control. A shed kiln is exactly that: a shed that has been adapted to be a kiln. You install fans in the shed (more on building a shed kiln later), and by turning them on and off, you can increase or decrease the air circulation to help the drying process.

Now that you know some of the different types of small-scale kilns, we’ll talk about determining which is right for you.

Picking the right small-scale kiln for you

How do you know which kiln works best for you? Let’s talk about each kiln to figure out why you might want one over another.

First, solar kilns are a great choice for those who want to save money on energy costs or are concerned with sustainability. They power themselves by solar energy and don’t generate any CO2 emissions.⁶

Because they don’t require conventional energy sources, they are also a great option for woodworkers in developing countries or remote locations.⁷

Next, a dehumidification kiln is a good option for those living in locations that experience more varied weather conditions and inconsistent sunlight (think, northern United States). In these places, it may often rain, and in the winter, there may not be enough sun to power a solar kiln.⁸

Lastly, a shed kiln is the right choice for you if you want the simplest kiln option. All you have to do is use an existing shed and add fans to circulate air.

But it’s not the choice for woodworkers who need their wood dried in a more timely manner. A shed kiln is only a step up from letting your wood air dry, so it’s not the speediest option.

With this general idea of what kilns work for what situations, it’s time to get into the nitty gritty of building each of these kilns for small-scale woodworking projects.

How to build a wood kiln

Let’s go through each of the kilns we’ve been talking about and highlight how to build each of them.

How to build a small solar kiln

These steps, taken from the Oregon Wood Innovation Center’s plans, are an easy-to-follow option for those looking to save money by building their own solar kiln.

First, figure out the location of your kiln. The area should:

• Get as much sunshine as possible (roof should face south)
• Be level
• Have good air circulation

Also, plan for the kiln to be raised off the ground in one way or another—whether with cinder blocks, railroad ties, or some kind of cement foundation. If it’s resting on the ground, the floor of the kiln will deteriorate, and all your hard work will go to waste.

Your location will need to be big enough for the kiln size you choose.

To determine the size of your kiln, note what you want the maximum capacity of the kiln to be in board feet. Then, divide that by 10 to find the area of the roof in square feet. For example, if you want to dry 450 board feet, your roof should be 45 square feet.⁹

Next, frame the kiln floor. You can use 2×6-inch joists and cover them with 5/8-inch plywood on the top and bottom. You’ll want to use pressure-treated wood and “exterior” plywood so that the solar kiln will be durable.

Afterward, mount the floor joists with hangers and insulate the floor with either a blanket or solid foam insulation.

That said, there are some insulations you won’t want to use. Avoid poured-in or blown-in insulation. And steer clear of insulations with a foil vapor barrier. They are likely to trap moisture, which won’t aid your cause of drying wood.¹⁰

After you frame the floor and before you build up your walls, determine the roof angle. This is extremely important for solar kilns, as, without the proper roof angle, the kiln will not work as efficiently as it could. In order to get the proper roof angle, make it “equal to its latitude in degrees north of the equator.”¹¹ For example, Wisconsin’s latitude can range from 42.5 to 47 degrees. A roof angle between those two is ideal: 45 degrees.

Now it’s time to construct the walls. For this step, use 2×4-inch studs and ¾-inch plywood. Be mindful when framing out the kiln door since you want to be able to fit the wood pile through it.

Also, frame out four 1-foot square openings for vents. You should place two on the top and two on the bottom. Then, cover them with some kind of screen material to keep rodents, birds, and other animals out. Construct simple doors, as well.

The paint job inside a solar kiln is particularly important. The entire interior, including the ceiling and floor, should be painted in flat, black paint. Because the color black absorbs heat, this ensures maximum heat absorption.

For air circulation, you will need a baffle to hold up a fan. Construct the baffle using ¾-inch plywood and fastening them to the side walls. Mount the electric fans close to the roof to avoid pockets of dead air.

The fans that you choose are important. You don’t want fans that are made of plastic, as the temperature inside the kiln can get higher than 150° F and melt the fans. According to the Oregon Wood Innovation Center, you’ll want multispeed, metal window fans. These should be aimed toward the front of the kiln.¹²

Lastly, cover the kiln with a roof. Ideally, the roof should be made of one or two layers of translucent fiberglass, plastic film, or glass.¹³ If you choose to do two layers, you may decrease drying times.

Once you choose the material you want for your roof, apply a silicone caulk—one that doesn’t harden—to the surface of the frame in order to seal both materials to each other. Then secure with 1×4-inch treated wood strips.¹⁴

Now, you have a completed solar kiln!

How to build a small dehumidification kiln

Taken from the USDAFS’s plan by Neal Bennet, these instructions go over the basic process of building a small-scale dehumidification kiln. They can be adjusted to suit your needs for larger/smaller kilns, etc. These instructions are designed to work with a specific dehumidifier: the EBAC LD800.¹⁵

Let’s start from the bottom up.

First, build the floor frame using 2x4s on 16-inch centers, meaning that you’ll place the center of the joist every 16 inches. The total dimensions of the floor frame for this specific kiln are 174×65 inches.¹⁶

After you’ve framed the floor, attach the frame to 6-inch by 6-inch by 16-feet timbers to elevate the kiln off the ground and keep moisture from seeping through the bottom. Insert lag screws through the bottom joists.¹⁷

Next, add insulation to the floor frame between each of the joists. To protect them from any moisture that might seep through the plywood floor (which we will install next), add a layer of plastic film (6-mm plastic film should work fine).¹⁸

On top of it all is the plywood layer, which should be fastened to the joists with nails. This is the floor of the kiln. Make sure that the seams are sealed, and put the extra effort in to seal the nails with construction caulk to make them even more moisture-proof.¹⁹

With the floor completed, you can begin working on the walls. We’ll start with the sides.

The short sides of the kiln are constructed in the same way as the floor: using 2x4s with the center of the stud every 16 inches. These specific walls are built at an angle. At the lowest slope, the height should be 42 inches, and at its highest, 52 inches. Two of the studs should be flush with the outside edges. All the other studs should be cut to fit.²⁰ All cuts can be angled 9 degrees.

Repeat this process for the other side.

Now, you’ll want to put the back together. Like the sides and the floor, construct the back using 2x4s, with studs on 16-inch centers. The dimensions should be 42 inches tall and 167 inches wide.²¹

After the back is completed, attach it to the floor and sides, making sure that it’s flush with the edges of the floor and both sides.

The front header is constructed similarly to the back and sides. Its dimensions are 14 inches tall and 167 inches wide. Attach it to the sides of the kiln, ensuring that it’s level.

Before building the rest of the front and top of the kiln, you’ll want to insulate all the walls. Use a vapor barrier, and make sure that it’s facing the inside of the kiln.

Next, complete the walls by nailing ½-inch plywood inside of the kiln and apply siding to the outside of the kiln. For this outside, you can use ½-inch plywood or T-111 siding. Caulk all the seams between plywood sheets.²²

For the top of the kiln, start by framing it the same way that you framed the rest of the kiln. The dimensions should be 183×73 inches.

Then, nail some of that ½-inch plywood to the frame—but only to one side. This is the ceiling of the kiln. Nail the top to the walls of the kiln, making the overhang even on all sides. Seal the spaces between the ceiling and the walls with caulk.

Insulate the top by using fiberglass insulation; aim it so that it is turned downward. And like you did with the bottom of the kiln, attach a 6-mm plastic over the insulation and a ½-inch sheet of plywood over the plastic.

You may be wondering if you need a roof on your kiln.

The answer varies depending on where your kiln is located. If you plan on keeping your kiln in a garage or workshop, then you don’t need a roof. If you plan on keeping the kiln outside, then you will need roofing, like shingles.

Congratulations—the outside of the kiln is done!

This is where it gets a little more complicated, but following these steps carefully will help.

First, use the illustration below from the USDAFS to cut out parts A and B to the specified measurements.²³

Next, fasten parts A and B to the kiln (the floor, ceiling, and wall) using ¾-inch softwood stock. Then—also using ¾-inch square softwood stock—attach a diffuser made of pegboard across the back of the kiln. Use the same softwood stock once more along the vertical seams between pegboard pieces.

Attach the foam baffle that came with the EBAC LD800 to the back of the first sheet of pegboard, 16 1/2 inches from the unit and 7 inches above the floor.²⁴

Now for the doors!

Start by framing the doors using 2x4s. The frames should be approximately 38×42 5/8 inches. However, the best way to size the doors is by measuring the dimensions of the total opening of your kiln. The height should be determined by subtracting ½ inch from the opening height. And, the width of the doors will be the total width of the kiln divided by 4 (be sure to subtract ¼ inch from the width of each door to accommodate the hinges).²⁵

Cover one side of the door frame with ¼-inch plywood (this will be the side that faces inside the kiln), and like the other parts of the kiln, insulate with a vapor barrier turned toward the inside of the kiln. Like the outside of the kiln, cover the outside face of the doors with plywood or T-111 siding.²⁶

Note that the hinge placement will be different depending on which door you are attaching it to.

For the outside doors, the hinges are placed on the outside (and, therefore, visible when looking at the kiln). The hinges that connect the inside doors to the outside doors, however, are attached to the inside of the kiln (and aren’t visible from the outside). Before attaching these hinges, you can shim the doors about a ¼ inch off the floor, which will make opening and closing the doors easier.²⁷

Next, attach latches to keep the doors closed. You should also add weatherstripping to the doors to seal any gaps. And to finish up, add a pair of handles to make opening and closing the kiln doors effortless.

The finishing touches of your kiln involve the control box, cables, and drain. Mount the dehumidifier (in this case the EBAC LD800) control box on the outside of the kiln. Then, drill a 2-inch-diameter hole below the drain pan of the dehumidifier unit.

The drain hose and power cables will run through this hole to the outside of the kiln. This same hole will be used to pass the temperature probe through to the inside of the kiln. The probe should sit about 2 feet above the kiln floor.²⁸

Once all the cables are through and the probe is in, you can seal the rest of the hole with expandable foam.

Finally, take a moment to seal any other gaps with caulk. Choose a paint or stain for the outside of the kiln, which will not only improve its looks but also protect it from the weather (if it’s going to be outside).

At last, your kiln is ready to be used.

If that felt like quite the process, the build for our last kiln will be one of the easiest.

How to build a small shed kiln

The plans for this small-scale shed kiln come from Woodworker’s Journal.

First off, you need a shed. Part of the appeal of a kiln shed is that you can convert an existing shed, buy a prefabricated kit, or build the whole shed yourself. If you opt to build the whole shed yourself, check out some of these plans:

• How to Build Your Own Shed from Scratch
• 10×12 Gable Shed
• 8×8 Shed

One thing to consider before you settle on a shed is the size. When it comes to kiln drying wood on your own, bigger doesn’t always mean better.

Woodworker’s Journal recommends an 8×12-foot shed for a single stack of lumber, 12×12 for double stacks, and 12×16 for triple stacks. This gives you enough space for all of the lumber as well as enough space to easily load, unload, and check on the lumber.²⁹

Also, if you are going to build your own kiln, take every precaution to insulate it well (consider taking similar steps as for the dehumidification kiln in the previous section).

Lastly, you may want to hire an electrician to satisfy the electrical requirements of the kiln. Because this type of kiln is larger than the previous two kilns (and because it’s outside), powering the kiln with an extension cord isn’t an option. You’ll need power sources for a heater, dehumidifier, fan, and steam generator.³⁰

One of the keys to transforming a regular old shed into a kiln is understanding the importance of directing airflow within the kiln. This will keep the wood from end checking, warping, and case hardening (when the outside dries faster than the inside).³¹

This is particularly important if you’re drying green lumber or lumber that’s straight from the sawmill. If the wood has already been air dried, it’s a bit more forgiving.

To maximize airflow within the kiln, Willie Sandry, writer for Woodworker’s Journal, uses attic fans. These fans should be rated for 1,600 CFM. You can purchase electrically reversible fans, or you can do what Willie does:

I came up with a simple hardware solution. A lazy Susan with 180-degree detents mounts the box fan to the ceiling. I then manually rotate the fan boxes halfway through the drying cycle.³²

This is an easy and cost-effective hack.

After installing the attic fans, place a household dehumidifier inside the shed. As the wood dries, you’ll need to remove water from the dehumidifier, either by drilling a hole in the wall and running a drain tube through it (note the instructions for this in the previous section) or by removing the water tray and emptying it manually (which is what Willie opts for, as it gives him another variable to track: water volume).³³

The last component of your shed kiln is a small electric heater to maintain an adequate temperature in your kiln. You will generally want your kiln to be above 100° F. However, you will need a sterilization cycle to kill any insects present in the wood. This looks like 3–5 hours at 140° F or 10–12 hours at 130° F.³⁴

Your electric heater should have an adjustable thermostat and an automatic tip-over shutoff.

Now you’re ready to load your wood and take your shed kiln for a spin.

So we’ve gone over each of the small-scale kilns you can build to save money (and time) for your woodworking business. Let’s finish by talking about monitoring the moisture content of the wood inside your small-scale kiln so that you can keep your wood in tip-top shape.

A key part of kiln drying your own wood

From the very beginning of the wood drying process, use a reliable moisture meter to monitor the wood moisture content (MC) of your wood. Without monitoring, your wood may dry too fast—which can cause long-term damage to the lumber. On the other hand, if it’s drying too slowly (or not at all), something may be wrong with the kiln.

So, before you even load the wood into the kiln, use a reliable moisture meter to determine which boards should be your sample boards. This will help you consistently track the MC loss rate. These boards should be the wettest of all the boards you’re going to dry.

Why?

Because you need the wettest boards to be dry enough.³⁵

A good rule of thumb is to measure the MC of the boards at the beginning and middle of the kiln drying process. Then, as you near the end of the drying cycle, repeatedly measure the MC of the boards.

You don’t want them to overdry. Also, as you get closer to your goal MC, you’ll need to decrease the temperature of the kiln.

That’s where a drying schedule comes in.

Be mindful that your drying schedule will vary based on the number of boards in your kiln, how thick they are, and their species, so it’s best to look at sample drying schedules. You can check out a few here.

You’ll want to aim for 10% MC for softwood lumber and 7% MC for hardwood lumber. Both of these measurements are for indoor use. For outdoor use, 12% MC is usually acceptable for both hard and softwoods.³⁶

A reliable moisture meter, like the DS500 from Bessemeter, will give you results you can trust, guarantee properly dried wood, and, therefore, give your clients the quality they deserve (all while maintaining your stellar reputation).

So, build your kiln, invest in a moisture meter, and make your dream of kiln-drying lumber come true.

1. Design and Operation of a Solar-Heated Dry Kiln for Tropical Latitudes, United States Department of Agriculture Forest Service. (↑)
2. Ibid. (↑)
3. Operation and Cost of a Small Dehumidification Dry Kiln, United States Department of Agriculture Forest Service. (↑)
4. Ibid. (↑)
5. Ibid., p. 2. (↑)
6. “Solar Dried Lumber Moisture Concerns – Solar Kiln,” Wagner Meters. (↑)
7. Design and Operation of a Solar-Heated Dry Kiln for Tropical Latitudes. (↑)
8. Operation and Cost of a Small Dehumidification Dry Kiln. (↑)
9. “Solar Kiln Plans,” Oregon Wood Innovation Center. (↑)
10. Ibid. (↑)
11. Ibid. (↑)
12. Ibid. (↑)
13. Ibid. (↑)
14. Ibid. (↑)
15. Dehumidification Dry Kiln Construction Plans, United States Department of Agriculture Forest Service. (↑)
16. Ibid. (↑)
17. Ibid. (↑)
18. Ibid. (↑)
19. Ibid. (↑)
20. Ibid. (↑)
21. Ibid. (↑)
22. Ibid. (↑)
23. Ibid. (↑)
24. Ibid. (↑)
25. Ibid. (↑)
26. Ibid. (↑)
27. Ibid. (↑)
28. Ibid. (↑)
29. “Design and Operate a Small-Scale Dehumidification Kiln,” Woodworker’s Journal. (↑)
30. Ibid. (↑)
31. Ibid. (↑)
32. Ibid. (↑)
33. Ibid. (↑)
34. Ibid. (↑)
35. “Solar Dried Lumber Moisture Concerns – Solar Kiln.” (↑)
36. Ibid. (↑)