I seem to recall that a decade or so ago new energy efficiency codes were written by NAECA such that manufacturers would need to increase the efficiency of all domestic hot water heaters sold after 4/16/2015. Meant different approaches to gas vs. electric. As far as natural gas tank water heaters go, anything under 55 gallons got more insulation (making them bulkier), and anything over 55 gallons had an entirely different set of rules because they use more energy. For those larger heaters they would require a 'condensing unit' which retained heat in the heater making it more efficient, but because the exhaust gases were now cooler, they would no longer be able to be naturally atmospherically vented through a flue as in the past. Instead, they would now all be equipped with powervents (PV) and vented through a wall. Seemed gone were the days of a 55 gallon traditional, non electric PV unit, atmospherically vented through the chimney flue as before. I know that's what I read, watched, and was told. But now it seems that I see currently manufactured 75 gal. atmospherically vented (no electric power required) natural gas hot water heaters that meet current ANSI code being manufactured and sold by all major manufacturers. I ask for someone knowledgeable to help me understand this. We have frequent power outages (sometimes for days) and having hot water is a lifesaver, so when it's time I would like to replace my old water heater with exactly the same type of non PV venting (flue/chimney) unit and want to know the code compliant options available. Thanks in advance for help understanding.
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