Why aren't we doing research into super insulated tanks for traditional heaters? Why can't I get a thermos bottle tank? (hard to lug up the stairs I suppose without breaking it...) There are already insulating attachments to keep the heat from radiating up the pipes and other such things
A regular tank keeps water hot always, even when you are gone for 12 or 24 hours or even days unless you shut it off and then have to wait many hours to heat up the water when you return. A water tank is almost like keeping the motor in your car at a constant idle waiting for when you may decide to take a drive.
James, my old water heater actually had some thick insulation between the tank and the outter jacket; there's a tag on it that says it's insulated to an R-16.7 value. I almost never hear the burner come on unless I run the hot water faucet for at least two or three minutes but it does keep going for about 15 to 20 mins after someone takes a shower to bring the cold water which entered back up to temp. Most of the time throughout the day, it just sits there, full of hot water, pilot on only, ready to be used. I did shut the gas off to my old heater the night before but there was still enough hot water for me to wash up this morning. I was discussing this with my friend's dad (who's also a plumber and installed the new tank) this morning as he was checking to see if an R-16 insulated model would fit. Most common, cheaper water heaters, he told me, are R-8 insulated.
The new water heater is also insulated to the same value. I didn't time it exactly but I think it took a little over an hour from the time we started it up to the time it reached the set temperature. I checked it out a few more times but I didn't hear the burner running until after I took a shower towards the evening.
Maybe in a colder area, it may lose heat faster to have the main burner come on a few times during the day or if we go on vacation for more than a day or two days, it may also have to reheat the water that cooled inside the tank.