I am looking at buying my first house with a summer/winter hookup. The house is in Eastern PA, and has a 1000 gallon oil tank and a small propane tank for the range and dryer. My question is this, what exactly is a summer/winter hookup, and what are the pro's and con's? Never running out of hot water? I assume you cannot buy a water heater that's oil fired? Would it make sense to get a larger propane tank and use that for hot water?

Thanks in advance!
Bryan