I open both valves but in cold weather when the heater is going to be used I carry a spare in the back of the truck (get it off my BBQ pit). Otherwise I don't care if they are both empty as I only use them for traveling to run the fridge. Hot water heater-electric, fridge-electric, stove, what's that? Never used. Last 2 rigs never had the oven turned on. Stove to vent the air for the fridge. Boondocking, yep that's when I only have water and electric hookup.