When evaluating hot water heaters, you must prioritize heating efficiency (EF rating) and recovery rate, which determines how many gallons of water can be heated per hour. For electric models, verify the heating element material (e.g., Incoloy or stainless steel for corrosion resistance). For gas models, check the venting requirements (Atmospheric vs. Power Vent). Additionally, ensure the tank lining uses high-quality glass-lined steel or stainless steel to prevent premature rusting and extend the product lifecycle.