# Tankless Water Heater with Recirculation Diagram



## Ghostmaker (Mar 2, 2013)

http://www.rinnai.us/documentation/...Rev_D_design_manual_tankless_water_heater.pdf
Contact Rinnai


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## md2lgyk (Jan 6, 2009)

I don't know the details, but I remember reading that some tankless heaters are designed to accommodate a recirc loop while others are not. I suspect it has something to do with the flowrate needed to kick the heater on. I have a gas tankless but no recirc loop. Doesn't bother me to have to wait a few seconds for hot water since all I used it for is showers anyway.


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## Live_Oak (Aug 22, 2013)

Did you calculate the incoming water temperature in winter with the ability of your unit to give it the temp rise? I've had a tankless for 19 years, but even here in the sunny South, I have to throttle down the flow rate to get more heat transfer in the winter, which reduces it's output to a single fixture use. I'm sure that it gets MUCH colder where you are vs. me, so just wanted to check to be sure you've done the math. I've not heard of a successful tankless install that far north because of this issue.


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## toddmanqa (Oct 31, 2008)

*Recirculation is ok with Rinnai*

Per the instruction manual, Rinnai is OK with a recirculation loop as long as it is controlled by something (timer, etc).


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## beenthere (Oct 11, 2008)

Live_Oak said:


> Did you calculate the incoming water temperature in winter with the ability of your unit to give it the temp rise? I've had a tankless for 19 years, but even here in the sunny South, I have to throttle down the flow rate to get more heat transfer in the winter, which reduces it's output to a single fixture use. I'm sure that it gets MUCH colder where you are vs. me, so just wanted to check to be sure you've done the math. I've not heard of a successful tankless install that far north because of this issue.



Here, we consider a 120,000 BTU unit, a small water heater. Most of them are 199,000 BTUs for year round hot water.

The OP's unit, is good for around 1.6GPM at a 90°F temp rise. A bit small for filling a bath tub for a hot bath.


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## Javiles (Dec 12, 2011)

Not sure what your looking to accomplish with this set up, maybe i am getting stupid in my old age. i see a couple problems on a set up that will accomplish nothing, are you looking for instant hot water on demand?? or..out of all the tankless set ups the only ones ive seen work relatively descent are units with secondary reservoirs on the larger units.


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## md2lgyk (Jan 6, 2009)

Javiles said:


> Not sure what your looking to accomplish with this set up, maybe i am getting stupid in my old age. i see a couple problems on a set up that will accomplish nothing, are you looking for instant hot water on demand?? or..out of all the tankless set ups the only ones ive seen work relatively descent are units with secondary reservoirs on the larger units.


I was thinking the same thing. Were I to want instant hot water at the one faucet where I don't get it (kitchen), I'd install a small point-of-use unit in the sink cabinet or down in the crawl space below. Don't really care, since the dishwasher has its own heater.


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## toddmanqa (Oct 31, 2008)

*Setup explanation*

This setup utilizes a hot water circulation pump. When a person walks into the bathroom/kitchen, a motion sensor is activated and which starts the pump, which fires the Tankless Water Heater.

The pump is pumping water in a recirculation loop. Each of the bathroom and kitchen fixtures is on the loop. 

The pump runs until a 103 degree temperature on the pump is reached (so all the cold water in the recirculation loop is delivered to the Tankless Water Heater). When a motion sensor is activated, it times out for 3-5 minutes during which the pump won't be turned on.

The idea is that the pump is not running constantly, and thus the TWH is not running constantly.


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## md2lgyk (Jan 6, 2009)

That sounds incredibly inefficient. How many times a day does somebody walk into, or pass through, the kitchen and NOT use any hot water? Or go into a bathroom and not use any? In my house, that'd likely be 50-60 times a day, and there's only three of us.


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## toddmanqa (Oct 31, 2008)

*Kitchen motion detector changed to push button*

I am convinced by the last post in regards to kitchen traffic: I will change the motion detector in the kitchen to a push-button near the sink that will activate the pump.

Now that I've head people's opinion in regards to system design, does anyone have any comments in regards to the actual parts/placement of the plumbing diagram: one-way valves, expansion tank placement, shut-offs, etc.?


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