If I Shut Off Water to the House...

While away, if I shut off the main water to the house and drain the lines…and shut off the electric hot water heater, (in fear of potential for another deep freeze)…what negative effects might one expect when re-starting the system? Yes, there will be air in the line, but what else? Will there be ill effects on the hot water heater and/or its contents? Or, can I simply undo everything and start the house’s water system up as if nothing changed??? I just want to be sure I know what I’m getting into. Somehow, my good deeds never go unpunished! :smack:

I should add: Let’s say the house water is down for 10 days.

Anything of which I should be aware?

You shouldn’t have any major problems at all. I used to do this at my vacation house every winter. It’s important to shut off the hot water heater first, otherwise you will burn out the heating element. The worst I ever had turning the water back on was some sputtering when the air got blown out.

You shouldn’t have any major problems, we still do this annually at a vacation house. Some times it’s helpful to take the screens off the faucets since we tend to get extra sediment with the sputtering.

Don’t you have to do something with the drain traps? Maybe add anti=freeze?

ETA: Or will the house still be heated to at least, say, 50?

Whenever my wife and I leave the house overnight - regardless of season - we shut the water off at the main supply valve. I relieve system pressure at one of the faucets before we go, but I don’t drain the pipes.

With the pipes full, there’s no worries about leaving the water heater on (though if we’re going to be gone for more than a day or two I’ll set the dial to “VACATION”).

I suppose with the pipes full there’s still a risk that freezing temperatures could rupture the system if the furnace craps out during cold weather. But:

-this is a pretty small risk
-if it happens, the amount of water that leaks out will be limited, since the supply is off
-it’s not worth the pain-in-the-ass to me of draining/refilling the entire house system to mitigate that small risk
-this is also why I don’t bother putting antifreeze in the drains/toilets during cold-weather absences

If your home’s water system has been shut off/depressurized for more than a day or two, some dissolved air may come out of solution and collect at high points in the piping. When you start running the faucets, these bubbles can create a water hammer effect: the air passing through the faucet lets the water behind it speed up, then when that water slams into the valve restriction, it suddenly decelerates, creating an intense pressure surge in the pipe system. This is similar to what happens when you shut a faucet very rapidly causing the water in the pipes to come to a very sudden stop; it stresses the piping, and in extreme cases (large air bubbles and high flow rates) can cause damage. When we return home, I try to run the faucets at low/modest flow until I’m confident that most of the big bubbles have been purged from the system. If you take the trouble to completely empty your water pipes before departure, then this will be even more of a concern when you return.

If you do empty your pipes, then yes, you’ll want to shut off your water heater completely.

Recently with the polar vortex, I heard of a townhouse which under the condo association was fitted with sprinkler pipes which diverges from the primary water main. The water was turned off and emptied when it was vacated but the sprinkler system wasn’t and those pipes burst with the deep freeze. Rare and unlikely but just wanted to throw that out there.

Draining and recharging a household water system can produce one troublesome result. It can dislodge crystals of "Lime’ that can move through your system and create problems with washer-less taps ( the crystals score the smooth seal contact areas). the trick is to do a throughough flush of the system, and start by turning all taps on full blast and letting them flow for 3 minutes after the last “blast” of air through the pipes.
Additionally, if risk of freezing is real, remember to empty your toilet tanks by flushing, as they will crack if frozen solid