i am a plumber. first off, you will actually not use that much energy using the second tank. what happens is the first tank will heat the water up then it will be transferred to the second tank as you use water. so the second tank only gets hot water. it uses very minimal energy and almost un, noticable on the bill. the second thing is the new hot water tanks are so wel insulated, if you tried to waste your time insulating it i would be amazed to see even a 2 dollar saving per month. as for instantanious hot water heaters, i think they are crap. chances are you will have to resize your gas line to put it in. about 95 percent of the time that is the case. they are also garbage because the heat a low volume of water, this is done by blowing a flame over a 1/4 inch coil. so all that you have to supply your house with hot water is 1/4 inch. the nxt problem is the costof them at about 3500 usually. the other problem is that since it is 1/4 inch with calgarys really hard water they tend to scale up. i have seen some scale up completely within 2 to 3 years. they also take a bit of time for the water to heat up so you will find yourself running them for a little bit longer than normal to get the hot water. so in the end are you actually saving money or spending it. if you are looking to get a new tank put in which is good idea if it is 10 years old send me a pm and i could maybe help out