The standby loss in a 40 gal NG atmospheric vented DHW heater set at code temperature of 120 degrees is 4 to 5 therms --- A MONTH
This season I am paying less than a dollar a Therm
I got this data before closed combustion became the norm -- and I expect that has reduced the standby loss to 3 to 4 therms of energy a month.
So not so "huge"
Case in point -- you buy the new appliance form Sears for 350.00 bucks - over a 5 years it uses 30 to 40 bucks of energy just sitting around - so total cost of having 40 gallons of hot water ready for instant use for 5 years === less than 600 bucks
What did the instant heater cost and do you think it will last longer than 5 years and deliver the same GPM?
Do you believe it can operated cheaper per gallon of heated liquid?
If you live alone -- I suppose