Please refer to the details in my previous post. If you find errors, you won't bruise my ego if you let me know what those mistakes are. There is only one variable, and that is the price of gas, which in my case is $0.915 per therm at the moment. My apologies for stating "at the current price of natural gas"; I should have given the actual cost. However, the price of gas this week or next month is irrelevant for the purposes of
*comparing* tank vs. tankless heaters (the thread subject & my current ambition), as are weather, incoming water temp, etc. I am comparing one type of gas water heater, a storage tank type, to another type of gas water heater, a tankless type.As to my estimated payback time of 8.1 years, that is based on the current 91.5 cent per therm price. And my estimate is probably off by
10% one way or the other. As the price of natural gas goes up, which it probably will, the payback time will shrink accordingly because the tankless will consume fewer therms over a given time period than a tank-type heater.Regarding your comment on the downside of endless hot water, you raise a valid point. Another poster previously did as well. So far, that does not appear to be an issue in this household, which consists of two teenage sons and me. In my case, sewer charges are flat-rated i.e. are not tied to water usage. So the only lurking "hidden costs" for this endless hot water -- and the gas to heat it -- would be minimal to unmeasureable, I think.
After this morning's flurry of hot shower-takings, my older son took off to spend new year's eve day with friends. Only two of us remain. The current time is 3:30 PM PST, and no hot water has been used since all those showers. I wonder how many times the old tanker would have cycled on and off during that time? Wait! A lady friend is coming over later this afternoon, perhaps she'll take an "endless" shower. Perhaps I'll even encourage her ;^)