Water Heater Plumbing Issues

[Zydeco]

We are replacing our Raritan 1700 water heater. Our fresh water system is set up like this: From the tank, the water goes to the pump, then to a Jabsco accumulater, then to a sediment filter. Attached to the "out" port of the sediment filter is a "T" fitting. One line from the T fitting goes to the cold water faucet, the other line goes to the water heater. There is a check valve installed in the line to the water heater, which I assume is to prevent heated water from backing up into the cold water line and/or sediment filter as the water heats up and expands.

I have two questions:

1 - the installation instructions for the water heater call for the installation of a vacuum relief valve in the cold water supply line (the line from the T to the water heater). The purpose of the vacuum relief valve is "to prevent back siphoning which could cause the tank to empty and element to burn out."

Question: is this vacuum relief valve really necessary? I am having a hard time imagining a scenario in which 6 gallons of water would "back siphon" out of the water heater which is installed lower than the water tanks.

2 - Because of the check valve installed in the cold water supply line (the line between the T and the water heater), when water heats up in the water heater it expands and a little water vents out of the safety relief valve. The instructions for the water heater calls for installation of a two gallon expansion tank in the cold water supply line which I suppose would take care of this issue, but we do not have the room to install one of these. I could probably find room to install a second small accumulator in the cold water supply line, but I don't know if those can tolerate hot water.

Any suggestions? Or should I just leave it the way it was? I can live with a little water venting into the bilge, but it didn't seem quite right.

As always, any help is appreciated.
Dave

[James S]

I haven’t heard of that valve.
The fact that the water heater is lower may or may not mater depending on where and how the cold water inlet is situated on the tank.
But I agree with you...between the pressure system and the check valve it seems unlikely that you would empty the heater through siphoning.
What kind of pump do you have?
I bought an accumulator and decided not to install it...I have a VSD and it seems to work well...the little bit I've used it!

[FraidNot]

ahh - you have just helped me explain some of the bits and pieces in my system - thanks!! I can't help with your question though - sorry.

[donradcliffe]

Leave things alone. Your system is pretty much the standard. The check valve will prevent you from losing water from the heater. There may be some venting from the relief valve if you heat a cold tank of water, but its not critical as long as you vent to the bilge.

A bigger issue is whether the temperature in the shower fluctuates as the pump cycles. Some people have reported success in installing a thermostatic mixing valve on the outlet of the heater.

[Zydeco]

Originally Posted by donradcliffe

A bigger issue is whether the temperature in the shower fluctuates as the pump cycles. Some people have reported success in installing a thermostatic mixing valve on the outlet of the heater.

I don't notice much of a temperature fluctuation as the pump cycles, but I might just be missing it - the showers are very short and I'm just happy to have something other than cold water.

James - I'm not sure what kind of pump it is. Just a typical pressure water pump. It's probably a basic Jabsco of some kind.

[Eleven]

Put a bottle under the vent valve outlet, saves pumping the bilges.
The heating element needs to be flooded to prevent burning out. Being at a low point is fine IF there's a cut-out sensor on it!
I'm on the kettle and flannel system. Tea first, damp shower later.