I have a 2nd home in West Virginia mountains used on weekends. It gets quite cold there and when we leave, I turn off the water and open the faucets (hot and cold) in the basement to drain the water lines in case power goes out so the pipes don't burst. I leave the heat set at 50 degrees. I have a Rinnai RL75i tankless water heater. Should I do anything to the water heater if I'm draining the pipes? So far I've just left it on and done nothing to it, but it just dawned on me that this may not be a good idea.