Guideline 16-2003 from the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), provides techniques for properly selecting dampers for the most common economizer relief system applications (return fans, relief fans, and non-powered relief) and minimum outdoor air control strategies. The guide, “Selecting Outdoor, Return, and Relief Dampers for Air-Side Economizer Systems,” addresses the application and sizing of outdoor, return and relief dampers used to control outdoor air intake for economizer cooling, minimum ventilation outdoor airflow for indoor air quality, and building pressure. Control damper selection and sizing are a critical first step in the design of control systems. But many designers select economizer outdoor air, return air, and relief/exhaust air damper sizes and damper action based on rules of thumb that are not valid or valid only for certain applications, according to Steven Taylor, P.E. "This improper selection and sizing may cause improper temperature, flow, and pressure control and other operational difficulties," Taylor, chair of a committee that developed a new ASHRAE guideline on damper selection, says. To order ASHRAE Guideline 16-2003, contact ASHRAE customer service at 800-527-4723, or visit www.ashrae.org.