The wife doesn't like the house being set at 55 degrees
so she (and the teen) take long showers, only leaving
the bathroom when the 50 gallon ho****er tank runs cold.

My propane ho****er heater is set to something like 135 degrees.
That means a lot of hot water is going down the drain.

I wonder - is there a calculation done on how much
energy it takes to heat 50 gallons of water with propane
versus how much energy it takes to heat a house by 5
degrees with propane?

Maybe it is cheaper to just heat the house more?