Interesting, thanks.
Do you remember how much gas you used before and after this, say in the summer time when house heating most likely is not on the bill?
I have a 40 gal unit and use 1/2 therm per day when no home heating is needed, 2 people.
Well, in fairness we also replaced an aging furnace with a 90%'er at the same time. So our drop in usage was substantial. Our gas budget went down nearly 40% (between the new tankless and furnace) when natural gas was skyrocketing. It has continued to remain fairly static over the last several years as natural gas has continued to rise. Obviously it's hard to say what you might save.... but probably not as much as a family of four. Three females under a single roof produce an INCREDIBLE amount of laundry. And, we rarely eat out so cooking is done every day (gas appliances) as well. My guess is our usage (and thus savings) would be a lot higher than yours.
Another REALLY nice thing is in the mornings during the school year, all four of us can shower/bathe in short order without having to "wait" for the water to get hot. It took nearly an hour and a half in the mornings with the tank (if not longer) by having to wait between showers/baths for the water to heat back up. And whoever was last.... usually got luke warm at best. Now, we can all go back to back to back and have all the hot water we want. The four of us can be in and out of the bathroom in 30 to 40 minutes. Hell.... that alone has made it worth every penney I spent.
What I was REALLY worried about was the increased water usage that everyone was talking about even back then. But, like I said, I bought the proper sized unit for a family of four with outstanding flow rates. My unit will kick on with just a trickle of water. Others, need a higher flow to "get going." Do I have to "wait" for maybe 10 to 15 seconds longer to get "hot" water?.... yes. But, with the low flow rate, I'm using hardly any water before it gets hot. Probably the same as I did with the tank and opening up the faucet and waiting for the hot water.
As for shaving like someone mentioned earlier, shave in the shower.... it's better for your skin since the steam produced in the shower softens your whiskers considerably making for less skin irratation. Once again.... a properly sized unit will give you plenty of hot water whenever you need it, save money on natural gas usage and take up far, FAR less space than a huge tank.
By removing the big 'ol tank.... I was able to rework my return air drop to the furnace increasing my air flow capacity and giving me room to install a super high efficiency April Aire filter. The previous return air drop to the old furnace was barely large enough and was squeezed right up against the furnace causing turbulance right where the air "turned" to go into the furnace. There was also zero room for any type of higher efficiency flitration. Now, with the drop a bit farther away and a little larger, it allowed us to install turning vanes at the bottom of the R/A drop which smoothed out and thus increased my air flow considerably. So, my whole HVAC system (both heating AND cooling) operate with more efficiency.
Finally, I also installed a control pad that monitors incoming water temperature and allows me to micro manage my water temperature to the exact degree I want my hot water. Yeah, the big tanks have the dial on the gas valve, but you have no way of knowing exactly what your hot water temp is. Mine, if I want my hot water to be 123 degrees.... I set it at 123 degrees and that's what I get. We had some friends visiting a couple of months ago with little kids. I turned the water temp down to 115 degrees with a couple of pushes of a button to make sure they didn't scald themselves. Probably not all that necessary.... but it was nice for my own piece of mind.
