I love a good calculation. So does my friend Al Zelicoff, who offers us a doozy of a set in today’s Journal energy tip, providing the back-of-the-very-large-envelope calculation on how much you can save by turning down the thermostat on your water heater:

320 pounds of water X (140 – 60) = 25,600 BTUs or about 1/4 of a “Therm” which is what you are billed for on your bill (currently about $1.20 per therm with tax).  This would be the amount you would use per day (and add a little bit because gas water heaters can not be 100% efficient since some heat MUST go up the flue) if you used 40 gallons of 140 degree hot water.  So, in a month (30 days) figure about 8 therms for hot water heating in this scenario.