Thanks folks!

Sorry, I should have added one more bit of information to my question: assuming that each tank is filled with standard city supply water, whatever temperature that might be coming in at any given time of year.

I'm just curious because we recently replaced a 15 year old 40 gallon tank with a 75 gallon tank. I can already tell that we're getting far more hot water than we did before, but it's hard to tell just how quickly it recovers. I was just wondering if we should be expecting faster recovery than the 40 gallon tank had, at least to get back to the amount of water we were used to before the replacement.


Yeah, I think there was some confusion here. I didn't say the tanks were empty at any point. I meant after they were used. Besides, there's no real point in asking how fast a 40 gallon tank will heat 75 gallons of water


It sure will! And it'll demolish my bank account "on the fly" too!

I'd LOVE to get a tankless heater, but cost is the #1 issue. Not only do they tend to run at least twice (usually three times) what our 75 gallon heater cost, they also don't deliver enough hot water for our shower. We did go a bit all out on our master bath, with four body jets, rainshower, and handheld shower. Even with just the body jets there isn't a tankless heater on the market that can keep up, particularly in the winter.

It's possible to actually combine two tankless heaters, but then we're talking somewhere in the range of $4-6K, and that's just for parts.

Granted, some of the money I'd spend on a tankless would be made up in energy savings, but the initial investment is SO high.


Yeah, that's the part of the word problem I accidentally left out. I meant that both tanks started filled with cold water.


I'm using BTU to describe the heater the same way the companies who make them do. They're advertised as 40K and 75K BTU water heaters. They have gas heating elements. Other than that, I have no idea what I'm talking about