Q: What is the EMC in Wyoming? I want to make sure that I dry the lumber to the correct final MC for a new client there.

A: The EMC (equilibrium moisture content) of the outside air in Wyoming varies with the time of year. For example, Cheyenne, November through June, is 10.5 percent to 10.8 percent EMC and July through October, 9.7 percent to 9.9 percent EMC. For the same time periods, Casper is 10.1 percent to 12.3 percent EMC and 9.0 percent to 10.3 percent EMC. Sheridan is 11.4 percent to 12.9 percent EMC and 9.2 to 10.9 percent EMC. (Exterior EMCs for many U.S. and worldwide locations are published in the U.S. Forest Products Lab Research Note FPL-RN-0269 available from the Lab at One Gifford Pinchot Dr., Madison, WI 53705.)

As air is heated, the EMC drops, so the EMC inside a house or office will be lower than outside. On the other hand, plants, cooking and showers from daily living will add moisture. Further, if the conditions drop much below 6 percent EMC (30 percent RH), we find that the dry air is uncomfortable and we will probably humidify the house or office. In brief, the interior conditions in Wyoming will seldom exceed 8 percent EMC and will often be close to 6 percent EMC or even slightly drier.

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