These wholesale and manufacturing outlets in Atlanta manufacture air conditioning systems and distribute them via a network to retail dealers and outlets. Manufacturers and wholesale suppliers work in a network with dealers all over the country or state, depending on the scale of operations. Sourcing can be flexible and the order amount varied. Wholesale dealers supply the distributors who in turn take the products to the retailers. Air conditioning units are now manufactured with emphasis on energy efficiency and certification, along with efforts made to tap reneweable sources of energy. Modern units are also much quieter and easier to maintain. Many come with filters for microbes and other impurities. Air conditioning, done by HVAC (heating, ventilation, and air conditioning), is now considered essential for contemporary societal comfort.