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What you'll find on this page: Reading insulation values when buying a new heater has recently gotten more complicated.

Once upon a time, figuring how much insulation a tank-type water heater had was easy. Right there on the label, there was an R rating, just like with wall or ceiling insulation. The higher the number after the "R," the thicker the insulation.

Ah! The good old days! Adios to "R". Nobody seems to use it. Rheem and its subsidiaries, Ruud and Richmond, dumped R factor and embraced Energy Factor, or EF some years ago. They said it was more precise. Other manufacturers still mention in some of their spec sheets how much insulation there is in inches, one inch being approximately R-8. But sometimes nothing is said. One might infer that silence means the minimum, while a mention means someone thinks it's a selling point.

EF comprises insulation, tank design, burner design, draw rate and other factors. It's important to remember that an electric heater will always have a much higher EF than a gas one, yet in some parts of the country, an electric tank will cost you a lot more to operate than a gas one because of utility rate structures.

So more of it now is up to you to sort out. You can still use EF, especially to compare different models, and you can look for insulation figures in the online spec sheets of manufacturers that offer them. The Department of Energy issued new rules for residential water heaters in April of 2015 and changed how it calculates EF. Many new electric heaters will have much more insulation than in the past, to comply with those rules. There are changes for gas, too, but that's not as clear.

Be aware of some of the idiosyncracies. The new rules require any gas heater over 55 gallons to be condensing, and any electric beyond that to be heat-pump. Both of these technologies are much more efficient, so you'll see high EF numbers. They're also much more expensive. It may not be worth it to you to spend the extra money. It will depend on your situation.