DHW Loop, Circulator Pump Method

[Boomerj]

I just installed a loop on my propane water heater by tapping into the T&P valve (top) and drain valve (bottom) ports. The loop runs through a 20 plate HX nearby. My Rheem direct vent water heater has an inducer motor mounted on the top, and it plugs into an outlet on the top of the unit, which is powered by the water heater's control panel. I unplugged the inducer motor and plugged in my circ pump. The theory was that when the water heater calls for heat and sends power to the inducer motor, the circ pump will run instead. Because there is a vacuum switch in play, the propane will never fire because the inducer motor is not running. It worked great! Except it never shut off. After about an hour (130 degrees at the bottom of the tank) I unplugged the circ pump and plugged in the inducer motor. The inducer turned on for a half second and then shut off, presumably because the vacuum switch allowed power to the circuit board and the unit then realized there was no longer a call for heat. So then I took the vacuum switch out of the equation (shut off propane of course) and tried it again. It still just ran and ran.

Does anyone have a suggestion of how I could wire this so that the circ pump runs when the water heater's internal aquastat calls for heat. My only other thought would be to install another aquastat, but I can't think of an easy or good way to do that.

 

[Boomerj]

Wiring diagram for the Rheem water heater

 

[Boomerj]

Photo of the ECO and Thermo control terminals inside the 110V portion of the water heater's panel.

 

[taxidermist]

I would imagine that when the WH does not fire the brain keeps the vent fan going as a safety. I just used a flow switch and a flat plate so I have on demand hot water.

Rob

 

[ALASKAPF185]

WEll in a perfect world you would have a well on the tank to place another aquastat , like on storage tanks or indirect water heaters. You still can do this with some creative piping and using one of the existing ports,like the drain. Add a tee and install an aquastat to measure the tank temp, set your temp limits and wire via the common on the pump. Leave the rheem as is from factory, just adjust the temp limits above the pumps limits. Some pumps can be ordered with an aquastat, like on the taco 006 series just for this application.

 

[Boomerj]

I tried the flow switch method. It was not sensitive enough to turn the circ pump on when flowing hot water full bore at the kitchen sink or even with a shower running. I tried adjusting the sensitivity, but at the most sensitive setting it would not turn back off. Just short of that setting it would not turn on often enough to keep the propane burner from firing often.

 

[ALASKAPF185]

Flow switches are not meant for this application, and by the time you pay enough money for a good one that works, you've exceeded the costs of doing it the correct way

 

[bigburner]

Looks like your theory should be correct, the only thing that cycles fan on is T-sat. it should work. Unless now you are washing enough water pass the t-sat location that it wont cycle off. This because you are now adding cooler water below the t-sat not above like it came from the factory. Plug it back in and see if the t-sat ever opens, bet it don't. If it does then your pump will turn off, the low voltage side is not a factor because of open pressure switch. Valve it down some "slow down the water" Is that a cast iron pump??

 

[Boomerj]

Looks like your theory should be correct, the only thing that cycles fan on is T-sat. it should work. Unless now you are washing enough water pass the t-sat location that it wont cycle off. This because you are now adding cooler water below the t-sat not above like it came from the factory. Plug it back in and see if the t-sat ever opens, bet it don't. If it does then your pump will turn off, the low voltage side is not a factor because of open pressure switch. Valve it down some "slow down the water" Is that a cast iron pump??

I am drawing water from the bottom of the tank, sending it through the HX, and then putting it back into the top of the tank. I measured the temp of the water at the bottom of the tank and it was at 130 degrees, enough to melt the heavy plastic container I used to draw the sample. I knew at that point that the water was hotter than usual and the heater should have shut down. I suspect as was stated earlier that the circuitry keeps the vent fan going, regardless of the temperature when the burner has not fired. Maybe I can wire my circ pump directly to the thermostat. I will try that tonight and report the results.

 

[bigburner]

Check and see if t-sat is open, LOOK at the ladder diagram and tell me how it can keep running if it open. Is it touching the tank did you have out, I have seen this before with hot water recirculation lines, it can get weird when the HW is being used, usually the tank starts dumping water.

 

[taxidermist]

I tried the flow switch method. It was not sensitive enough to turn the circ pump on when flowing hot water full bore at the kitchen sink or even with a shower running. I tried adjusting the sensitivity, but at the most sensitive setting it would not turn back off. Just short of that setting it would not turn on often enough to keep the propane burner from firing often.

The first one i used would not turn on the pump for me. I switched to this one and it even turns on the bathroom sink at the far side of the house.

http://www.pexsupply.com/Mcdonnell-Miller-115600-FS6-1-1-Flow-Switch-High-Sensitivity

Rob

 

[woodsmaster]

Rob I like the way you have yours set up. How Big of a flat plate do you use ? Do you have to clean it often?

 

[taxidermist]

Rob I like the way you have yours set up. How Big of a flat plate do you use ? Do you have to clean it often?

30plate with well water first year using it but so far so good! I did put clean outs on it so i can flush it every year.

Rob

 

[in hot water]

here is the type of switch you should try. These "make" at a flow of .5 gpm. This is the switch used on many tankless water heaters to fire them up when a faucet flows. Now available via a branch in Wisconsin.

hr

 

[Humplumb]

You could use the bottom t stat on the hot water heater .Tie that into a switching relay that would turn on the pump when you have a call for hot water and it would shut off when tank is at temp.Just a thought.

 

[taxidermist]

here is the type of switch you should try. These "make" at a flow of .5 gpm. This is the switch used on many tankless water heaters to fire them up when a faucet flows. Now available via a branch in Wisconsin.


hr

I talked with a supplier in the us and they wanted me to buy something like 10 of these or they would not deal with me.

Rob

 

[Boomerj]

big burner was right, there is no way the pump should stay on if the thermostat is open. Turns out it was just a coincidence that the thermostat opened moments after I aborted my trial run with the circ pump. I dialed down the thermostat last night while it was running and it shut off.

I noticed right after I installed the loop that there was air in it. Not sure how it escaped, but I did not hear it last night and the run time is much much shorter now. I'll be putting an air purger on it the next time I shut the water down (hopefully not too soon, it ain't broke...). I think this method is going to work for me. I had looked at the high sensitivity flow switches and figured that is what it was going to take, I just couldn't justify spending $252. I probably spent more than that on all of the trial and error with methods to avoid it, but maybe someone else can learn from all this. In summation, this method cost me $94 for the pump, $40 for the extra pipes and maybe $30 for the fittings. $164 and water that is not hotter or colder than it was when heated by propane. No need for a thermostatic mixing valve or worry that my kids are going to be accidentally scalded...

Thank you all for weighing in.

 

[taxidermist]

My DHW heater does not have a power vent so a flow switch was my only choice. Glad you are up and running.


Rob