Hot water heaters generally run on heating oil, propane, natural gas, or electricity. If yours runs on heating oil, then you’ll want to make sure to check your heating oil tank periodically throughout the summer to prevent a runout. Fortunately, hot water heaters do not use nearly as much heating oil as your furnace or boiler will when heating the entire house.
Expect an average daily usage of 0.5 to 1.0 gallons of heating oil to keep the water hot. If you have a larger house, or an instant hot water recirculating pump that constantly moves the hot water throughout the house, expect your consumption to be on the higher end of the range.