There are different heating element sizes for electric heaters and different burner btu ratings for gas heaters. You can have a big tank and low heating output, a small tank with a high output, or any other combo of those.

My solution is to buy the highest output heater with as big of a tank as you can find, crank the output to just below the flamethrower output level, and shower with my wife. It fixes most of the problems with a benefit of naked wife time.

I live on the gulf coast with a shitty power grid so we have gas powered tank heaters so it still works during an outage, otherwise I would probably go tankless.