OREGON STATE UNIVERSITY

Sun-dried lumber possible even during Oregon winters

10/09/1998

CORVALLIS - Oregonians can easily harness enough of the sun's energy to dry lumber in about four or five weeks, though it might take a little longer during a typical western Oregon December, says an Oregon State University professor.

Using natural gas or electricity for conventional lumber drying can cost $25 to $75 per 1,000 board feet. The only cost of using a solar kiln is the electricity for the fans.

Jim Reeb, a wood products specialist with the OSU Extension Service, built a trailer-mounted solar kiln so he could experiment with drying wood in various areas of the state. So far he's dried myrtle wood in Corvallis and western juniper in Klamath Falls.

"Certainly on the east side of the state during the summer months you could air dry lumber as fast or faster than in a solar kiln," Reeb said. "However, drying lumber too quickly can cause drying defects such as cracking and splitting. In addition, exposure to the elements can discolor the wood."

So even in areas where sunshine isn't an issue, a solar kiln may help prevent the weathering and drying defects that can result from air drying, he said.

Reeb said that the prototype solar kiln OSU built was relatively small so it could be moved on a trailer. It can accommodate about 800 to 1,000 board feet with a maximum length of 18 feet per board. To make the kiln stationary, it might need to be larger to accommodate more wood, he said.

The OSU extension specialist added that his design used Plexiglas to make the kiln more durable during moves. But small woodlots could save money and dry more efficiently by using old glass windows.

The solar kiln includes an insulated box with fans to help circulate the air. Woodlot owners not wanting to build one themselves can purchase commercial solar kilns for $8,000 to $10,000, according to Reeb. Some can accommodate as much as 10,000 board feet per load.

A general guideline for installing the solar collector part of the kiln for optimum drying during the summer is to make the slope of the collector about the same as your geographical latitude. By increasing the slope by 10 degrees, you can increase the drying efficiency during the winter, while only slightly decreasing the summer efficiency, Reeb said.

Reeb said people interested in building a solar kiln can call him to discuss the pros and cons of drying Oregon tree species. He can be reached at 541-737-4233.