Profile: Mainstream designs and manufactures custom air handling systems & components for commercial, industrial & specialized applications. Our custom air handling unit delivers years of reliable, trouble-free performance in situations where large volumes of precisely conditioned air are critical. Our custom built cooling and heating coils are used primarily for direct replacement or specialized applications. They are engineered to outperform and outlast standard coils, & are available in a broad range of materials & configurations to fit many applications. Our coils are certified to ARI Standard 410.