Furnace for heat, Water heater for hot water, Stove for cooking...etc etc
some larger rigs, though, are now 'all electric, meaning that they no longer have any Propane needs or appliances - though they do employ diesel water heater and furnace air.
'14 Palazzo 33.3 bunkhouse 34' diesel
KingTailgater2 Dish HD, 100w/5a SOLAR, BlueOx
100,000+mi since '14 - US, Alaska, Canada - Hiawassee, GA! (also, '14 Gulfstream Amerilite and '07 ForestRiver Rockwood) : )