Growing up, our house did have oil fired hot water heat (with the big old radiators, one under every single-pane window) but the water heater was natural gas. Go figure.
Back to oil fired hot water, IIRC the recovery rate was more than the rate that the water flowed through the water heater. So in theory, you could not run out of hot water. I think the smallest size oil nozzle was 0.65 gallons per hour or something like that (we're dealing with 50-year-old memory here so don't hold me to it) and that combined with the BTU rating of heating oil, which I have no idea what that is now, meant that you could run the shower for as long as you wanted and wouldn't run out of hot water until the oil ran out. Or something like that.
Edit to add: I'm sure one of the engineers here will "crunch the numbers" and let me know if I'm mistaken. I will concede that I may well be.
Back to oil fired hot water, IIRC the recovery rate was more than the rate that the water flowed through the water heater. So in theory, you could not run out of hot water. I think the smallest size oil nozzle was 0.65 gallons per hour or something like that (we're dealing with 50-year-old memory here so don't hold me to it) and that combined with the BTU rating of heating oil, which I have no idea what that is now, meant that you could run the shower for as long as you wanted and wouldn't run out of hot water until the oil ran out. Or something like that.
Edit to add: I'm sure one of the engineers here will "crunch the numbers" and let me know if I'm mistaken. I will concede that I may well be.
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