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trols and pump housed in one end and a door at the other end for loading the lumber using a dolly on tracks. He said that setting up the kiln was a straight- forward operation. With a level concrete pad inside the building, all Jesse had to do was to maneuver the 7,500-pound containers in place, using a couple of car dollies. “Installation wasn’t that bad,” Jesse explained. “The controls and pumps are enclosed in one end of the container, all connected and ready to use. It took us less than a day to set both kilns in place and wire and plumb them.” Surprisingly, the kilns run entirely on single-phase 208-volt electricity with 50-amp serv- ice. The well-insulated container is heated electrically and the water vacuum pump requires less than 3/4 gal- lon of water per minute when it is running. Jesse esti- mates that the average operating cost is about $38 per thousand board feet. Jesse’s kilns are capable of drying up to 2,000 board feet at a time, but normally run around 1,500 board feet, depending on how efficiently the lumber is stacked. The kilns can handle up to 12-foot boards, so drying a load of 8-foot lumber leaves a lot of empty space. Although white oak takes a bit longer to dry than most other species, Jesse routinely mixes species, as long as the thickness is uniform. He says that he just punches in the thickness of the wood and the computer takes over, adjusting the pressure and tem- perature automatically. The fans are specially designed to operate efficiently in the hot, low-pressure environ- ment of the kiln and reverse the airflow direction peri- odically to ensure consistent drying. When the reser- voir that holds the water extracted from the wood is full, the kiln automatically opens a vent to equalize the pressure, pumps out the water, then returns to the drying cycle. When the wood is near the target mois- ture content of 6% to 7%, Jesse opens the kiln to check the moisture content with a pin-type meter. As he gains experience, he is getting better at determin- ing how much time it will take to finish the load. Most of the wood Jesse dries comes straight from the sawmill. Typically, 4/4 hardwoods dry in a week, but air-dried lumber (around 18% moisture content) dries in half the time. According to Jim Parker, many iDry kiln operators air dry their lumber to increase the throughput of the mill, but he cautions that defects that occur when air drying can affect the kiln perform- ance. “If you don’t air dry properly and the wood is case-hardened, it slows down the drying process, and you would have been better off putting the wood in green,” he explained. “Once wood is case-hardened, it is much harder to kiln dry, and it will still be case- hardened when it comes out of the kiln.” Other defects associated with air drying, such as discol- oration, warping, and cracking, can also be avoided by putting lumber into the kiln as soon as it comes off the sawmill. For this reason, Jim recommends end coating the lumber as soon as the tree is cut. Jesse takes it a 12 • Sawmill & Woodlot Loren Bates opens up a kiln to check a load of oak. The pressure inside the kiln is so great that a valve must be opened to equalize the pressure before the door can be opened. step further, applying end sealer to the last 4 inches of each board before loading it in the kiln. With walnut making up the bulk of the wood he dries, the extra care pays off. He showed me a stack of about 1,200 board feet of walnut. “You can see how straight it is. We had this lumber sold before we even had it out of the kiln. “I haven’t had any problem with warping or splitting. The wood that comes out of the kiln is just phenomenal.” To illustrate his point, Jesse opened the valve to depressurize the kiln. The air rushed into the kiln with a loud hiss. It took about five minutes for the pressure to equalize so that he could open the door. “This is from a red oak tree that was cut in downtown Bentonville for some construction,” he said. “It was about 52 inches at the base, 11 feet long, and milled by a local sawyer yesterday. We had him get as much quartersawn lumber as possible and got about 1,200 board feet from that one log.” He had to quarter the log with a chain saw to get it on the mill, and the boards are all marked and numbered so the woodwork- er can put the slabs back together, if desired. The wood will be used for countertops and tables by the restaurant where the tree was cut. “We’ll have to baby this load so the oak doesn’t crack,” he added. “It will probably take three weeks.” After inspecting the stack and taking a moisture reading, he closed the kiln and started up the vacuum pump. “This is the advantage of two small kilns over a single larger one,” he noted. “It lets us do special orders like this and still be able to run the faster-drying wood in the other one.” While the kiln is an integral part of Jesse’s business, he provides much more than custom drying. “If some- one wants custom sawing, we work with loggers and arborists who can cut down trees and network with sawmills that will cut them to the desired size before bringing them here for drying,” he explained. “We alsoPDF Image | iDry Vacuum Kiln
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