Hot water heater insulating jacket: How much savings

Measuring how much a hot water heater jacket saves.
In my case, very little. But it can save more if your hot water heater is poorly insulated, the hot water heater jacket is better than this one, electricity is expensive, and the jacket is cheap.
More about the spreadsheet I used at:
http://woodgears.ca/physics/r-values....

Please note that the W/m2 column in my spreadsheet had a formula error in it, which resulted im my heat-loss estimate being about 20% lower. So the payback period is actually more like 5 years. Still too long. But if your electricity costs twice as much as here, your water tank is less insulated, and you get a better insulating blanket for less, the payback could be less than a year.