If you like copious amounts of hot water but do not want to pay to have heated water just sitting around cooling off investigate the various instant hot water heaters. I have an electric but I am in a mild climate I have heard real good things about the gas fired ones. The boy scout camp even installed them in the bathhouses and the last shower is as hot as the first and no money is spent heating water when no one is home all week long.
I considered a flash style heater as an upgrade to
my 50 gas, 50,000 BTU unit. The flash burner is
128,000 BTU. It requires significant upgrades to
the vent. The vent upgrades alone would have
been $1,000. I replaced the heater with another
50 gal, 50,000 BTU from Lowe’s. Did all the labor
myself. Carted the old tank to the local recycler.
Total cost around $300 in parts.