Hope this is the right forum. I have a neighbor with an oil boiler because he has some hot water baseboard heat. Currently his domestic hot water is "driven" by an indirect hot water tank off the boiler.
Given oil's recent prices, he's considering switching just the domestic hot water to either electric or propane (he has propane at the property for a pool and cooktop in the kitchen).
Is there a relatively straight forward formula to compare the cost of heating a gal of water for elec vs propane vs oil??? I know oil will generate 140k BTU's per gal, propane 91k btu's per gal, and it takes 3412kWh of electricity to get to one BTU.
I'd be interested in seeing the formula to compare the costs differences for 1 gal of hot water. If necessary, I'd assume the oil burner at 80%. Not sure what the typical tank electric or propane hot water heater efficiency is.
Thanks in advance for any feedback.