"MLD" wrote in message
...

"desgnr" wrote in message
...
Would there be much difference in operating costs for a 40 gallon gas
water heater vs. a 30 gallon ?

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Dell Inspiron
Pentium dual-core 2.2 GHz
2 GB DDR2 SDRAM
Windows Vista Home Premium SP1

Energy req'd=f(weight of the water)----So with all other things being
equal, increasing the tank size by 33% (10/30), one would expect to see
the operating cost go up by 33%.
MLD

No, not really. The cost of maintaining the thermal mass will go up a bit,
but surface area for heat loss must be taken into consideration and it is
not linear. The cost of taking say, 20 gallons of hot water out of the tank
and replacing it with 20 gallons of cold water, is the same.