National Energy Control Corporation, Havertown, PA, has released the 20th Edition of the HVAC Guidebook. In addition to many pages of product information, the book includes helpful technical references and tips for installing and maintaining commercial HVAC controls. From pneumatic controls to electronic energy management systems, the book is designed for any technician that works on control systems. For more information, or to order a free copy of the 20th edition HVAC Guidebook, call 800/227-9800 or visit