The answer to eliminating cold drafts and/or flying pests each time the door opens is an Air Curtain.
Air Curtains create safe, comfortable environments by providing an invisible barrier at the door that separates (2) environments. A high velocity stream of air spread evenly across an opening will keep the cold air out while allowing you and you customers in. An air curtain over you main entrance can eliminate those cold influxes of air during those winter months and warm influxes during the summer while an air curtain over your receiving door can stop flying pests from entering the building. These are just a couple of examples of what an air curtain can do. These units can be provided with or without heat. An unheated unit is used to protect an opening while a heated unit can provide supplemental heat.