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I plan to shut off the main water supply to my 2 story house before leaving for a week on vacation. I have an AO Smith gas 'powervent' water heater in the garage that I would like to set to 70*F rather than turning it off. Since there are no issues with freezing pipes here in the SF Bay Area, I wasn't planning to drain the water lines within the house. Would the cold water feed on top of the water heater need to be turned off also?

Grant
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    No. Either turn the water AND the water heater off, or just turn the water heater down to 70F (VAC) and do not turn off the water. – longneck Jan 14 '20 at 21:35
  • OK, so in your opinion I should not have to shut off the cold water valve to the water heater if I shut off the main water supply and set the water heater thermostat to 70*F. Unfortunately I've read conflicting opinions. Some have indicated that there could be syphoning out through the cold water inlet if it isn't shut off. Others think it's fine to leave the water heater on without shutting the cold water valve to heater! – Grant Jan 15 '20 at 00:47
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    Yeah, that's a mistake. Normally, this mistake is borne out of a misunderstanding of how water heaters work. – Harper - Reinstate Monica Jan 15 '20 at 01:44
  • Do not turn off the main water supply. You still run the risk of siphoning with the main water supply turned off. – longneck Jan 15 '20 at 13:40

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I would turn the water heater to pilot if you turn the water off, pilot will keep a small amount of heat there and unless it gets crazy cold would help prevent freezing. I grew up in that area and rarely will it get cold enough to freeze pipes inside the house even if you turn the heat way down,

I never recommend turning the furnace totally off as that can cause cracking of joints if Sheetrocked.

If you turn the water off the water heater should be on pilot or turned off. I have replaced a few water heaters over the years that were damaged from cycling with no water.

Ed Beal
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  • The lowest setting for this water heater is 70*F. It doesn't have a pilot as it's electronic ignition. Not sure what you are implying regarding the "furnace". – Grant Jan 15 '20 at 00:40
  • Many folks trying to save a dime turn the heat off and then end up with tons of cracks, you did not state why you wanted to turn the water off , I always recommend turning the power off if electric and turn to pilot if gas , I added the info on the furnace issue with cracks as those that want to turn off water and power usually do the same with the home heat. – Ed Beal Jan 15 '20 at 01:11
  • Thanks Ed! I'm leaving this morning for a weeks vacation. I'm turning the main water supply off and setting the water heater to 70*F without shutting off the cold water line on top of heater. I can't believe how many conflicting opinions are out there!! – Grant Jan 15 '20 at 16:30