My oil-fired conventional oil-fired tank hot water heater in a vacation house needs to be replaced. My options are
1. Simply replace it.
2. Run a propane line from an existing propane tank outside and replace the heater with a propane-fired tankless one.
LEAVING ASIDE THE RELATIVE COSTS OF PROPANE AND OIL (which can change from time to time and which seems to me to be generally a wash, given energy content, fuel price, and efficiency), my question is whether the amount of energy lost from leaving a 50-gallon tank heater running and unused when I'm not here is worth the cost of running a propane line ($$$$) and installing a more-expensive tankless heater (I estimate >$$$$ more expensive for the heater).
Most of the year, I only use the house on weekends, so I would estimate that for about 40 weeks, the hot water gets no use during the week. (I know I can shut the heater off when I'm not here, but occasionally guests or a cleaning person comes, and I like to have the hot water on for them.) So, again, the question is, how much energy is lost just from keeping a tank of hot water for 5 days without use.
(For what it's worth, the house is on Long Island, NY, and I keep it at 50 degrees during the off-season when I'm not here.)