Specify with Confidence. Specify Greenheck Air Distribution. Grilles, Registers, Diffusers and Air Terminal Units Available Now! Greenheck is adding to the HVAC industry's widest product selection! Our new grilles, registers, diffusers (GRDs) and air terminal units (ATUs) are designed, engineered and tested to meet a wide range of performance and aesthetic criteria. Complete your project with Greenheck! Leaders in Air Movement since 1947. Specify with Confidence. Specify Greenheck. ©2023 Greenheckhttps://www.greenheck.com/products/air-distribution?utm_source=ASHRAEJournal&utm_medium=printad&utm_campaign=March2023&utm_content=AirDistributionpage