indirect vs power vent water heater

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Posted by jay darcy on November 11, 2001 at 12:50:11:

I need to replace a 50 gallon 12 year old Bradford White gas-fired
power vent water heater. Sears will install a Kenmore 9 year model for
~ $900. Other quotes I've gotten are $1000-1200. All of these have an
"energy factor" of 51-54.

I have an existing gas 150,000 btu gas boiler, with an AFUE of 83. I
can get a 45 gallon Ultra Stor installed for $1800.

My gas bills for hot water alone run $ 50 -60 a month, or $600 - 700
/year ( 4 kids and $10/mmbtu gas ). Is the energy factor and the AFUE
comparable? That is can I calculate the difference between the
direct-fired and the indirect fired by using a factor of .52/.83 ? In
other words, can I assume that the annual operating costs of the
indirect will be about 5/8 of the direct fired?

We have some complaints about enough hot water. One reason for choosing
the Super Stor is because we've been told that it's equivalent to a 75
gallon direct. Is this correct?

The Ultra Stor would be hooked up as a zone on the boiler. We use the
boiler for heat from October to May ( Connecticut ). Obvously, if the
boiler fails we'll get no hot water. But one plumber warned us not to
get an indirect, because it would cause the boiler run all year long,
resulting in a lower life-time. He also said the boiler was much less
efficient when it was only supplying heat to the Super Stor. This
doesn't sound right to me. Is it ?

In looking at indirects, I see a specification for "pressure drop"
measured in feet. I assume this describes the pressure required for
the boiler water to move through the heat exchanger coil. Therefore
a lower pressure drop is better. Correct?

Thanks for any help.

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