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[idahohay]

I know this topic has been covered many times before but this time a slight twist.

In this case, the supply from the OWB will not be in series, but a loop via closely spaced tees in the supply from OWB. This loop will have its own circulator. 

I have two choices,  either run makeup water for DWH through a fphe (would do it this way if I had much demand), or hook up a side arm heat exchanger and let it thermo syphon. 

I think a sidearm would be adequate for my needs but have only seen them hooked up in series on the way to a water to air heat exchanger so all the flow from the OWB would pass through the sidearm. 

How could I control the circulator so it would cycle on and off with the tank temperature?
  Is there a clip on aquastat that would do this?  I will be using a Caleffi or Azel pump controller for my zones and  I would still want to use the electric water heater as back up or in off season. 

If I used a fphe, there would still be a need to activate the circulator when there was a hot water demand. In this case maybe a flow switch? Any suggestions would be appreciated.

[slimjim]

It sounds to me that you are creating a primary loop and want the water heater to be on a separate loop than the primary, not sure why but yes it can be done with a strap on or a relay off your existing 220 volt aqua-stat, first can we ask why you wish to do this.

[ITO]

Must have an electric water heater and forced air system so no primary heat in the main loop in the summer?

[idahohay]

slimjim, I'm going from owb to fphe to in floor radiant.   I was up against some challenges trying to make it all fit under a stairway so things changed from the drawing I posted several weeks ago. (easy to fit on paper not under stairway)

I want to feed the exchanger for DHW as a secondary loop off the incoming line from OWB. Some of the reasons are  (1) I was given  two stainless 007's, and two stainless 006's.  If I calculated right, an 007 will provide barely enough gpm for my main fphe, but won't cut it if I add another heat exchanger.  I really like the idea of a stainless 007 at my stainless owb and having a spare is even better. 

Supplying a sidearm with an 006 might be a little slow on recovery although the flow will probably be as much or more than a lot of setups.  The temperature drop after the closely spaced tees would be less than if I were supplying a fphe, and when a set point of 140 deg. was met, the 006 would turn off.  This setup would simplify my plumbing in a space that wasn't meant to be. 

So any comments would be appreciated, and what parts might work   to control a pump with the water heaters aquastat. Would hope to leave the water heater to function as normal.

Forgot to add that I also acquired a small 20 plate with 3/4" inlets.  If it was installed so water heater supply passed through it, how could the flow activate the circulator?

[RSI]

If you use a sidearm setup to thermo siphon and only let it get up to 140 you will run out of hot water. The only reason they keep up is because the water is much hotter in the tank and the mixing valve supplies a portion of the water that comes out of the faucet. If you are running at the lower temperature it will deplete the tank much faster.

If you want to do it that way, use one of the 006 pumps to pump DHW through your 20 plate and another on the boiler side on the secondary loop. It might not be able to keep up to high demand but will be a lot better than the sidearm setup.

[idahohay]

Good point on the sidearm.  I guess one option would be to run the pump until the temp approaches boiler water temp.

A pump on each side if the 20 plate was my original thought, but am tempted to pump just one side and direct makup water for water heater through other side and see what I get. 

Still trying to figure out how to get the pump to come on when there is any hot water flow.

[slimjim]

You could use the existing aqua-stat on the water tank to control your circs, remember it is 220 volt and more than likely is hooked to a GFI breaker, if this is the case you cannot pull 110 from one leg to power your circs but instead will need to use a RIB relay designed for 220 with dry contacts on the lower side and power that side with a separate 110 source of power, this will allow control of the water temp in the tank but as RSI suggested you may run out of hot water fairly quickly.

[ITO]

 Maybe consider using a priority circuit on the DHW pump? The radiant heat will not lose much during a call on the tank, thats how I set mine up and it works well.

[idahohay]

ITO, the pump controllers I am considering both have a priority feature, but still need input to turn on the pump. That leads me to slims suggestion of using the aquastat on the water heater.

No GFI on my water heater. It is a (new) typical 40 gallon, 240 volt, two element in which one element at a time operates.  There is always 110 at each element, upper stat sends the other 110 to either the upper element or the bottom stat. Bottom stat can send the other 110 to the lower element if calling for heat.  But like any typical water heater, there is no neutral so where would the 110 come from for the pump? The only 110 on a 240 volt w/h is between one current leg and ground, its not wired with a neutral

[slimjim]

I have simply pulled power from one leg before and grounded off the pump but it should be on a GFI. In reality for safety, this is where the relay comes in. Why would you not simply run your primary loop from the wood boiler constantly through the sidearm?

[idahohay]

slimjim, I was trying not to add any more head to the loop so I could use my stainless 007, also the piping in my confined space would be simplified if I didn't add a sidearm to the boiler loop.  But, the more I think about it, just add the sidearm and be done with it. If the pump at boiler needs up sized, so be it.  Thanks for taking the tme.

[slimjim]

You are very welcome, thanks for seeing the light and GREAT question!

[RSI]

If you use the plate and the pump, you could put a temperature switch on the cold pipe before the plate so it turns on and runs whenever cold water runs into it. You might need to put it back a couple feet so it senses the cold as soon as possible. You might need to use a larger plate too but what you have might work.

The advantage of doing it that way is you can control the temperature without needing a mixing valve. Disadvantage is it makes the system more complicated or more to go wrong.

[Sprinter]

The 007 & 006 will do pretty good. There is also a way to do 2 circs in series, having only one come on during a heat call and the other runs constant, providing just enough flow on standby.
The Taco smart plus 006 circ I just did was doing 1.9gpm with 130' pipe, half of it was 1/2" pex.
Piping your secondary circuit with copper with have the least head, and try to keep pipe length to a min.
There is a stat on the bottom element for the elec WH, and I have used that to cycle the circulator and maintain tank temps without needing a mixing valve.

[idahohay]

Thanks for the suggestions.  Just ordered some parts to build a sidearm. If I go this route, I could always add the 006 on the domestic side.  Since I have a good size piece of two inch copper, I ordered two- 2x1x1 cxcxc Tees. (Looks like there is no such thing as a 2x3/4x1).  I plan to run 3/4 " type M through the center but read an advertisement for sidearms where the manufacturer boasted type  K or L as being safer, any merit to that? I'm guessing except for the multi tube type, most are type M.