If the units are in a RV then yes, they both may run on gas and DC (battery power). The furnace requires gas to provide heat and DC power to run the fan. A water heater may be gas or electric, but if gas, it requires gas to heat and DC power to ignite. If the water heater is electric it requires AC power to heat.
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If the units are in a RV then yes, they both may run on gas and DC (battery power). The furnace requires gas to provide heat and DC power to run the fan. A water heater may be gas or electric, but if gas, it requires gas to heat and DC power to ignite. If the water heater is electric it requires AC power to heat.