NG Water Heater... Why VAC rather than off?

[Wade Lippman]

I have natural gas water heater with an electric ignition. Everything says to turn it to VAC rather than to off when away for a while.
Why?
I turn the water off; does that affect the answer?

[Jim Koepke]

I have natural gas water heater with an electric ignition. Everything says to turn it to VAC rather than to off when away for a while.
Why?
I turn the water off; does that affect the answer?

You do not mention if this is tankless or a water heater with a tank.

With a tank, even when the water is turned off the water heater will keep the water hot, using gas.

jtk

[Wade Lippman]

You do not mention if this is tankless or a water heater with a tank.

With a tank, even when the water is turned off the water heater will keep the water hot, using gas.

jtk

It has a tank. I mean turning the power switch on the heater to "off" rather than leaving it on and turning the temperature to "VAC".

[Ken Fitzgerald]

I am guessing that VAC keeps it on but at a minimal temperature. If you turn it off, it could take a while for the water in the tank to heat back up to what most might call a useable temperature.

[Bruce Page]

The vac setting keeps the pipes just warm enough to prevent freezing, turn it off if you’re not worried about frozen pipes. I would not turn the water off, you will likely stir the sludge up at the tank bottom when you turn it back on. BTDT.

[Alan Rutherford]

... I would not turn the water off, you will likely stir the sludge up at the tank bottom when you turn it back on. BTDT. On the other hand, with a HWH (electric) well past its warranty date and having had one leak before, I don't like the thought of the tank leaking unchecked for a week or more.

[Kev Williams]

I'm still using a pilot type WH. When we leave even for the weekend I pull the incoming water valve closed. I don't mess with the temp, I want hot water when I return...

Having been thru a washing machine and a water heater dumping all the water they were holding in the past, THAT'S why I shut the incoming water off. And while gone no hot water is used so nothing in the tank stirs up when the valve is re-opened.

I believe the main reason for the VAC setting is to run a flame just often enough to keep the spiders from building webs in the burners and feed tubes...

[Jim Koepke]

IMO, if one feels there is sludge on the bottom of their water heater tank, it is time to hook a hose up to the outlet valve and drain off some of the sludge.

jtk