How to Build a Wood Dry Kiln
While processed lumber is widely available and generally adequate for most uses, you can nearly always save money and improve quality by drying your own "wet" (fresh-cut) wood with a home kiln. Building a wood dry kiln can be surprisingly simple if you have a good grasp of basic construction techniques such as wall framing. In addition, a solar-heated kiln is especially effective, efficient, and easy to operate.
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Things You'll Need
- Framing lumber: 2-by-6 and 2-by-4
- Tape measure
- Circular saw
- Hammer or nail gun
- Framing nails (10d)
- Insulation in strips/rolls
- Plastic sheeting (0.6 mm)
- Staple gun
- Staples
- Plywood (3/8-inch)
- Clear, corrugated polycarbonate
- Aluminum or rubber liquid sealant
- Paint brush
- Exterior paint
- Wall vents
- Doors (or lumber and hardware to build them)
- Window fans
Instructions
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Design your kiln. A basic home wood dry kiln is a rectangular box, but with a low wall in front, a full-height wall in back and a clear, slanting roof (typically angled at 45 degrees) connecting them. Kilns also usually have wide doors in the sides or back to let you load and remove wood, as well as vents in the back wall and fans inside to promote air flow. The most important dimension to determine is your roof, because the sunlight flowing through it heats the kiln and dries the wood. Each square foot of roof lets you process ten board feet of wood. Based on the roof size you need, figure out the measurements for your front, back, sides and floor. Be sure to factor in an extra foot of floor space to each side of your wood stack, again to allow airflow.
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Frame your floor with 2-by-6 lumber, setting your joists at 16-inch intervals. Set insulation between the joists, cover the frame with plastic sheeting and staple the sheeting in place. Lay plywood over the plastic, and nail it to the joists to create your floor.
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Frame your front, back and side walls with 2-by-4 lumber, setting your studs at 16 or 24-inch intervals. Remember to include rough openings for your door(s) and vents.Set insulation between the studs, and nail a layer of plywood to each side of each wall.
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Coat the entire interior with a liquid sealant that is rubber or aluminum-based. If you use aluminum, add a topcoat of black, rubberized sealant to help soak up more sunlight. Paint the exterior with a standard, light-colored paint.
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Frame your roof with 2-by-4 lumber, setting your joists at intervals wide enough to allow plenty of gaps for sunlight to pass through, but close enough to be solid and sound. Nail a layer of clear, corrugated polycarbonate on the top of the framing, and if you expect to dry wood during cold weather, nail a second layer to the frame's underside.
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Install wall vents in various walls using the rough openings you framed for them.
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Build support boxes for the window fans using 2-by-4 studs nailed to the roof frame 2 feet from the back wall. The boxes should support the fans at a height of 3 feet below the roof frame while allowing full airflow in front and behind them. When the frames are ready, set the fans in them.
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Tips & Warnings
Choose a kiln location that has ample room around it to let you carry long pieces of lumber in and out. For best results, orient your roof toward the south to ensure you get the most sunlight.
Never leave your kiln completely closed up when there is no wood inside. The interior temperature can climb well above 200 degrees Fahrenheit, so leave doors and vents open to let hot air escape.
