Water Heater Efficiency

The 50 gal tank in my water heater is leaking and I'd like to select a conventional gas replacement that minimizes my up front costs plus operating costs over the next 10 years.
I see that Rheem has two high efficiency series water heaters (Professional and Fury) that have .67-.68 "Energy factor". What is this?
The high efficiency GE SG50T12AVG is advertised to use 242 Therms of energy a year. If I know the BTUH rating and energy factor, can I calculate Therms?
For conventional gas water heaters, is better insulation the major difference between a standard model and a high efficiency model?
My wife suggested buying an insulating blanket that fits snugly around the tank to reduce heat loss. I'm guessing that if this would help, the manufacturer would have already added the extra insulation for units they market as high efficiency. Can anyone confirm that her idea will actually reduce our gas bill?
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They don't always go together, but the long payback is usually more important.

The higher the factor, the more efficient. Good for comparative analysis. It is the amount of energy delivered versus the amount of fuel used.

Use those numbers for a comparison of model to model. Your actual numbers will vary depending on family size, laundry, etc. .

One of a few factors. Better burners, etc.

Manufacturers have increased the amount of insulation so adding more will have little value as compared to 30 years ago. More is always better, but there are diminishing returns on investment
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Some new heaters cannot have a full blanket anyway, something to do with the new anti-explosion features. My son's new heater has holes all around the sides at/neart the bottom for part of this snti- explosion feature, and there was some sort of a warning about not adding a blanket.
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hr(bob) snipped-for-privacy@att.net wrote:

Right. Like a 1" layer of plastic and fiberglass will have some effect on an exploding water heater.
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wrote:

Sounds to me like they are trying to prevent the explosion-- not minimize effects.
Jim
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Maybe a controlled or even directional burst rather than let it decide how to go? The holes allow the vessel to rip letting the energy dissipate?
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wrote:

I believe thse holes are to prevent the entry of flammables gases or at least prevent a explosion.
Miners used to use burning candles for lighting underground while working. It was safe because the metal screen prevented the flame from igniting coal dust in the mine
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Ah, I thought these holes were around the tank, not the combustion chamber.

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wrote:

Another line to consider is the A O Smith Vertex series. They offer thermal efficiencies from 90-96%. They offer an almost unlimited supply of hot water. If you have a dealer in the area you might want to check them out. Richard
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