Just startig new concrete smoker with electric double burner as heat source. Question as to need of bottom air supply. Have top vents but no bottom vent. Don't really see any need for one?? I am a 7 month resident at the San Carlos (Sonora) Mexico who smoked Sierra mackeral for several years in a makeover refrigerator. I built a new home and had the contractor build me a cement smoker (about refrigerator size) onto the house. He put a well insulated door on the unit which seals well. I have a problem because he put 4 two inch pipe vents in the top and I am trying also to work out a way of cutting the vent size down to a realistic size. Always new challenges with any new startyup. Suggestions welcomed!! At 86 years of age I am switching to ribs and meats rather than fish. Always need a new challenge.