"Donna Ohl, Grady Volunteer Coordinator" wrote:

One thing that confuses me to no end is this EFFICIENCY thing.

If both a 50 gallon and 40 gallon water heater has the same 59 percent
efficiency factor ... do they cost the SAME to heat?


For the same water use, yes. Efficiency refers to non-electric heaters
(electrics are 100% efficient), and accounts for the heat loss up the vent pipe.
In other words, heat that doesn't heat the water.

Or does the 50 gallon water heater actually cost more even if it's the same
efficiency?


Not to heat the water, but over the lifetime, yes.

The reason I ask is I assumed they cost the same to operate but someone
said the smaller water heater will cost less to operate even if the
efficiency factor is the same.


True.

Can someone who understands this clarify if a larger heater truly costs
more to operate than a smaller volume heater even if the efficiency factor
is the same?

Although both units will use the same amount of energy to heat water, the larger
heater has a larger tank, which in turn means it has more surface exposed to the
outside. The greater the surface area, the greater the heat loss when you aren't
using water, which means the larger heater will use more energy to maintain the
hot water.

Now, if you live north of the Mason Dixon line and your water heater is inside
the house, then that isn't a total loss as you heat that escapes goes to warm
your house. It only becomes a problem when you want to run the A/C.

OTOH, if you live south of the Mason Dixon line or your water heater is in the
garage, then yes, you will pay a little more to run a 50 gal heater than a 40
gal. one. Is it significant? Look at the energy tag on the two heaters, but I
suspect the difference is less than $20/year. OTOH, you may find the larger unit
has better insulation, which may compensate.