Sidearm setup questions

[MrEd]

I ordered my flat plate heat-exchanger (5x12x10) and when it gets here I am going to add it as a pump-driven sidearm to 50G electric hotwater tank to get "free" DHW during heating system. I'll be using a brass circulator on the DHW side to circulate water out the top and back in thru the drain at the bottom, and the hot water will come in as a aquastat-activated zone off my distribution.

Couple of questions:

1. I need a tempering valve, on pexsupply they come in the 100-130 degree flavor, and the 120-160 flavor. I assume that these ranges refer to the desired *output* temperature correct? so I would be getting the 100-130 degree version?

2. Will a standard electric water tank have any problems when you "superheat" the water? How hot should I let it get? as hot I can? or should I put an upper limit on it?

3. My dishwasher is directly above my hot-water tank in the cellar, so it would be simple to feed it "untempered" water that potentially would be as high as 180 degrees, is this a good idea? or does it violate code? Seems that sending it 180 water would really give it some extra clean dishes.

4. What kind of fitting should I use to connect to the bottom of my DHW tank? It has a standard "garden hose" type fitting(don't know what they are actually called)..what do I add it to allow it to handle the pressure and not leak? Is there a fitting designed for this purpose?

5. What options are there to measure the tank temp to decide if I should call for heat? Going to try an aquastat at the top of the tank (where the pressure relief valve comes out), but was wondering if there was an easy *and safe* way to use the electric thermostat that is already built into the unit?

 

[Dune]

You may not need a circulator, most side arms work by convection
1Lower temp for sure. Don't want to burn anyone
2 Should be able to handle 180 fine. If you are going to use an aquastat and a mixing valve set it.
3Commercial dishwashers must run 180 degree water, not sure about residential, contact manufacturer
4You will have to remove this fitting, should be 1/2"I.P.S.
5Make sure you still have a pressure relief valve after you are done. Sounds to me like you should return the flat plate heat exchanger and install a super stor instead.

 

[MrEd]

I considered a superstor but the flatplate was $129, the superstor was $999, and the superstor wouldn't do me any good when I wasn't burning wood...all the other parts I already had, but thanks for the help on the other questions.

 

[rowerwet]

your best bet would be to use a shell HX and return the flat plate HX, using a shell hx you wouldn't need a pump just convection, for a good diagram of how this install works look at the cental boiler website.
you want a water temp no higher than 120 for the house water to keep from scalding anyone.

 

[Gooserider]

Code requires that the water delivered to the faucets be no more than 120*F to avoid scalding issues. NoFo has suggested that there is a particular Honeywell mixing valve that is better than most for this as it will allow better control on the mix temps. There is no problem superheating the DHW tank itself up to around 180 or so, but you shouldn't get much hotter or you may start popping the T&P relief valve.

Sending untempered water to the dishwasher can be done, and will help get the dishes a little cleaner, but whether it is worth it or not is debatable. You may discover problems with some allegedly "dishwasher safe" plastic items turning out to be not so good at withstanding the higher temperatures.

To connect to the tank, you will need to remove the drain valve, put in a nipple and a tee, then put the drain valve back in one branch of the tee, and the HX in the other. I would agree with some of the others on possibly wanting a different style of HX than the flat plate you mentioned.

Gooserider

 

[kabbott]

On my electric water heater there is a manual reset temp switch on the top element. If you exceed this temp you will not have any power to the elements.
I believe they all have some sort of protection from overheat, you may want to check so if the electric suddenly quits working you will know what to do.
Many T+P relief valves open well before the 210 degrees they are marked, mine opens at about 196(measured) so keep this in mind if you are going
anywhere near this high.

My dishwasher has a heater that I believe heats the water if it is not hot enough. Might save some KWH's if you send untempered water to your dishwasher.

An aquastat should work. The existing TT on the heater could be used depends on what the rest of your controls consist of and if you want auto switchover to electric.
Another option would be to add a snap switch type TT similar to what controls the elements now, just fasten against the side of the tank.

 

[Duetech]

I might be wrong but I think you should take the water out of the bottom of your hot water tank and return it to the top. The top is where most water heaters I have seen release water to the house. It's stratification at work. Cold water comes into the hot water tank through a long tube and forces the hottest available water to the top of the tank. Sidearms deliver the hot water to the top of the tank while taking the cooler water from the bottom through convection.

 

[wantstoburnwood]

The hot water should go in the top and cold out the bottom. That is how mine is installed and works good. Also I wired the circulator to the bottom switch on my water heater . I am going to wire a DPDT switch on the themostat so I can change from winter to summer (using the electric water in summer).