9bbafd4a_Duct_Heaters___Wattco_com__vs__Unfinned_tubular_elements_Finned_tubular_elements
[Unfinned Tubular elements] Can be installed close to a register or grill [Finned tubular elements] 
Maximize the heat transfer surface of the element
Duct Heaters - Wattco.com
Finned tubular elements