Water heater deficiency

I don't have a sidearm but I've never seen someone run the cold domestic supply to the bottom of the side arm. I tend to think this might be part of your problem.

How much water are you trying to heat in these two tanks? Why the second tank?

The more I look at this the less I think you're getting any kind of circulation through your side arm on the DHW side. The principle of a sidearm is to create a "current" in your tank as the water in the inside of the exchanger heats and rises and draws cooler water from the bottom of the tank. With your domestic cold water connected at the bottom I wonder if you can ever get these convection currents moving?

I suspect that stee6043 is correct about the cold water going strait through the sidearm. That does not explain why it worked for all these years though.
My DHW tank has only a cold inlet on the bottom and a hot outlet on the top. In my case I have the sidearm connected at the top the same as yours,
but the bottom I removed the lower heating element and made an adapter to connect the sidearm.

I would say that when you draw water the cold is going mostly through the sidearm and directly into the second tank.
Do you have any other taps on the tank you could use?

I don't know how big the tempering tank is but the way you have it hooked up you will only heat the water in the tempering tank as there is no way for any flow to heat the other tank. You need to connect a line from the drain on the gas water heater to the cold line on the bottem of the side arm. Having the cold plumbed like you have it works ok except you are only heating the one tank. I would also have the hot connection on the gas waterheater from the sidearm going into the portwith the relief valve. Put in a tee with the relief valve on top. By doing this you will be putting the hot water into the top and not going thru the drop tube on the cold side. Plug off the cold side on the gas heater.
also it works better if you have the hot boiler water going into the top of the side arm so you have the hotest DHW water leaving the sidearm.
Remember, the side arm works with thremo-flo. hot water rises pushing the cold water down making a circle. The hottest water will rise first and the coldest water will take it's place. You must have a circle flo path in both tanks. by having the tanks in parallel you can heat both tanks and will pull hot water from both.
leaddog

It sounds like your sidearm/tank setup is working. I think the problem is that your Hot water is going into the bottom of the Gas Heater (it may go in the top, but it has a pipe all the way to the bottom). So, your preheated hot is mixing with the Gas tank's water. Since it's likely hotter, then it stirs up and down, ruining whatever stratification existed in the Gas tank. So, all you get out finally is mixed up warm water.

Most Gas DHW tanks have a central chimney/heat exchanger. This makes them extremely poor containers in a standby mode, as the heat is lost up the chimney.
I'd either lose the gas tank, or set them up to both heat at the same time (parallel).

Every thing is good on the pic except leave the cold water comming into sidearm at the bottem like you had before. also make sure the hot water is going into the water heaters in the relief valve opening. The reason for that is there is a drop tube in the cold water side and that makes the water go to the bottem.. Just put a tee and put the relief valve on top. just cap the cold water off then. (the cold inlet on the water heaters)
You will have the water comming in from the sidarm at the relief valve and cold water going to the sidearm at the bottem. The cold water will also be coming into the bottem of the side arm.
The hot water will be comming off the hot outlet of both tanks going to the tempering valve. You will have to hook up a cold water to one side of the tempering valve and that can come from any place from the cold water
Also switch the boiler to top and boiler return bottem. You want the hottest water at the top.
Hope this helps
leaddog

Bugzapper said:

"Also switch the boiler to top and boiler return bottem. You want the hottest water at the top."

Are you sure about that? Most all of the drawings, especially from Central Boiler show the hot at the bottom and return at the top.
What is the reason to go the other way?

Did you notice that I coupled the two tanks from the bottom to the cold inlet in the side arm? Will that help the movement of hot water between the tanks?

What would the reason be for mixing cold- cold water with the warmed (from the bottoms mentioned above) cold water going into the side arm? Would the warmer go into the exchanger or would it mix?
Would a pump help this contraption?

Thanks for your help.

JB

Click to expand...

Yes you definitely want the boiler loop to go in the top and out the bottom of the sidearm.
A pump can help but adds to the expense and control complications, I think for average use you shouldn't need a pump.
your drawing in post #11 may work but you can still get flow through the bottom pipe which will let cold water flow from tank 1 to tank 2 when you draw hot water.
If I were you I would try this but leave out the the pipe on the bottom that connects the two tanks.

What puzzles me is you say it worked fine before, is your boiler temp lower now? Is your boiler temp lower than the set temp on the gas heater?

The ideal way to plumb a side arm is by itself, meaning no hot or cold DW lines tee'd into it, that way you have no bypassing. Meaning the cold water can't
flow strait through and out the hot outlet.

There is really no good way to connect two tanks using thermosiphon because of the bypass problem and if you use a check than it may not thermosiphon
or a least not as well.

Last If it were mine I would forget the two tank idea, Get one working right and you dont need it.( at least for an "average" family)