I'm not sure how old my hot water heater is. It works fine but i'd like to be prepared if it should stop working. Do I need to know about energy efficient options like a furnace (a80 or a90)?? Venting options (wall or flu)? Also, my current heater has a plactic insulated type of covering or blanket on it. Is this good? Does it keep the water warmer? Is there a site that I could learn about hot water heaters? Thanks for help on any of these topics & have a great day!