I have a question about what the proper method for bypassing (shutting down) a water heater is.

In solar hot water systems, a solar storage tank holds water heated by the sun. This water is fed into the existing hot water heater. Usually there is a three valve bypass so that when there is enough solar heated water to meet all the household needs, the water heater can by bypassed and turned off, so standby losses are eliminated.

Ideally when you shut down the water heater, you would drain it, I suppose. But since you never know if you'll run into a stretch of cloudy weather, I usually do NOT drain it.

This means that you have hot water in the water heater that cools off, thereby decreasing in volume, resulting in some vacuum in the water heater. People have told me that a tank could collapse under conditions like this. Also, if you leave the water sitting in it for months, there could be buildup of bacteria.

I usually have my water heater (actually a Lennox Completeheat boiler) turned off from April into October. I don't drain it, and I just open the valves and fire it up when the time comes. There is some noise when I open the valves, but it doesn't seem too violent. And we've never gotten sick...

Just wondered if anyone had thoughts on this!

Thanks,

Mark

Likely the tank is well able to stand any vacuum that develops from the water cooling. Water will vaporize to fill the volume. Be careful about allowing a sealed tank of water heat up. That can generate more pressure than any tank can stand. Pressure relief valves are required on hot water tanks. It would be easier on the tank to vent it to the atmosphere. A simple tee and valve would do. If you drain the tank, likely there will be a little water left in it. Could be a worse place for bacteria to grow than a full tank. Maybe the best thing would be to turn the power or gas off and let the hot water circulate through the tank.

Thanks. I agree that powering down the tank and just letting the solar heated water pass through it would eliminate my concerns. The downside is that there are extra heat losses from the water heater (which is not insulated as well as my 210 gallons of solar storage) and probably some extra lag in getting hot water. In the end, all of these concerns are probably minor.

Mark