"When I was a boy," Addin S. Batson was saying, "our hot water intake pipes ran through a coil in the furnance, and from there to a conventional water heater tank.
"In the water, when the furnace was on, we always hada tank of piping hot water - without even lighting our regular water heater.
"In the summer, when the furnace wasn't on, we lit the gas burner in our water heater. But the rest of the year we had free hot water from our furnace coil. It was a great energy saver, and I wonder why they stopped making that kind of furnace. Do you remember those furnace coils?"
No, Adin, I don't remember that type of furnace, and I'm sure that if we'd had one, I'd have remembered it. By the time I was 10, I was in full charge of two coal furnaces, and I'll never forget either of those monsters. I may have shoveled more coal in my time than John L. Lewis.
The water intake pipe in our house ran from the outside main to a cotinuous water heater that had no storage tank. It considered of three principal components a coil of copper tubing, a gas burner, and mechanism that turned on the gas burner whenever somebody turned on a hot water spigot.
In a few seconds, one could get a constant flow of hot water from this type of heater. Running out of hot water was unheard of. Our system had no storage tank and therefore didn't have to keep a tank of water hot all day when there was nobody at home to use it. Our system used no fuel until somebody needed hot water - and then it provided an unlimited amount of hot water at once.
I don't know why furnace coils and "instantaneous" water heaters are no longer being made. I can only guess that changes in the cost and availability of gas were involved. If you have some knowledge of either of these old-fashioned systems and can shed some light on why we no longer use them, I'd sure like to hear from you.