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Tankless Water heater.

Earl Weiss

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Plumber installed tankless Navien heater - Don't have model # handy right now. Replaced an AO Smith cyclone unit that could not keep up on busy days. This unit feeds all my solution mixing stations and Ts into a cold water line so water at the stations is warm, not hot and I adjust it for outside temp. Warmer in winter not as warm in summer. Bottom line was at 100+ CPH the AO smith could not keep up and this one does. The AO Smith replacement would have been about $6000 . This unit costs about $1500.00 . Planned plumbing in case I might need 2. But I don't.
 

2Biz

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How many GPM and at what temperature? My Takagi 199k Floor Demand Heater puts out 6.7 gpm @ 105°...That's 402 GPH....So yea, they can output a lot. Just keep an eye on the tiny inlet filter if it has one. It will plug easily if you don't have a larger pre-filter.
 

soonermajic

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100 cph, holy $hit! Who cares what it cost with that kind of volume! I am still curious about those HE water heaters. This tankless sounds like it may have the problem of not enough hot water volume beat...?
 

Earl Weiss

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How many GPM and at what temperature? My Takagi 199k Floor Demand Heater puts out 6.7 gpm @ 105°...That's 402 GPH....So yea, they can output a lot. Just keep an eye on the tiny inlet filter if it has one. It will plug easily if you don't have a larger pre-filter.
A little confused by your specs since these seem to be rated at X GPM at a certain temp rise. rise.
Here a 199K Takagi rated at 9.5 GPM for a 40 degree rise and 9.5 looks like max flow.
https://www.ecomfort.com/Takagi-T-H3-DV-N/p70551.html?gclid=Cj0KCQiAkfriBRD1ARIsAASKsQJgiuu9LZ6rhRNzWn8OFwumEn5xiICM5yJibhtRsC7Sg7dFWjIAOyAaAqDhEALw_wcB.
The Navien NPE - 240S I have is rated 9.8 at 40 degree rise with max of 11 GPM. https://www.navieninc.com/products/npe-240s/quickfacts
 

2Biz

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What I posted was actual. There is a readout on the front that toggles between inlet temperature, outlet temperature, and flow in GPM...Mine flows at 6.7 gpm at 40psi inlet pressure. If you look at the graphs in the Takagi instruction manual, the "Boasted" Max GPM stated is rated and based off 100 PSI inlet pressure. Anything less than that will not give you the advertised max flow.

On page 60 of the Navien manual, it shows the pressure drop curve. At 40psi, the max flow you'll get through the heater is 8gpm. Then temperature delta rise is secondary. Anything higher than 35° Delta (temp rise) and flow drops...

The advertised "Maximums" are a little misleading until you study the graphs and figure out what you're actually going to get at the Delta Increase you need and inlet water pressure. Actually at 40 psi inlet pressure and 105° setpoint (55-60° Delta Rise) mine is spot on comparing to the graph.
 

Earl Weiss

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The advertised "Maximums" are a little misleading .
When it comes to equipment and specs I figure they all lie (it's for some "Optimal" condition.) You just have to figure how much. FWIW after the plumber left I got a call that we were running out of water. Seems my guy didn't note the mixing valve which allows cold water to enter the hot water line feeding the mixing tanks was closed and only the hot line was feeding them. 6 Mixing tanks feed every wash with 2 more on higher packages. If you figure the flow jets averaged 4 GPM and run 75% of the time when we run steady that's 18 GPM so it's no wonder it ran out. Opened the mixing valve a little and problem was solved.
 

Earl Weiss

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. Anything higher than 35° Delta (temp rise) and flow drops...

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A little confused as to cause and effect. The above makes it look like you can set for higher temp and flow will drop. I figured temp was set and simply dropped if flow increased. Which is it?
 

Greg Pack

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Following the thread. I've got a raypack 199 BTU with a separate 100 gal tank and would love to free up the floor space.
 

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I have had a few paloma tankless water heaters. 199k units you can adjust the temperature rise by restricting the water flow with a dial on the front. i use 1 per SS bay. In my case I found using a single Voyager 80 gallon 199k water heater worked better for me. 1 unit supplies all the hot Water we need for 2 IBA and 4 SS BAYS.
 

Earl Weiss

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Following the thread. I've got a raypack 199 BTU with a separate 100 gal tank and would love to free up the floor space.
I thought about this since other locations, tunnels and SS have the typical Boiler, Tank circulating pump system. Some tankless now have circulating valves built in so you could plumb a return line, but IMO it's not needed. The tank less is basically instant, so I don't see the difference in water temp from from the point where it's hot i.e. the heater or the tank as being much of a factor.
 

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A little confused as to cause and effect. The above makes it look like you can set for higher temp and flow will drop. I figured temp was set and simply dropped if flow increased. Which is it?
Most demands that I know of limit flow to maintain the setpoint outlet temperature. If you look at the Delta Curve (Difference in inlet and outlet temperature) in the manual, the higher the Delta, the lower the GPM flow is to maintain the setpoint temperature. That's how my Takagi works and according to your Navien manual, yours is the same.
 

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When it comes to equipment and specs I figure they all lie (it's for some "Optimal" condition.)
LOL...They actually aren't lying! In the specs, they boast the "Maximum" flows. Its just the moon and stars need aligned before you can get those maximum flows! That's why when going to a demand heater, its extremely important to do your homework to find out how much capacity and Delta Rise you need and compare to the flow charts....
 

Earl Weiss

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Most demands that I know of limit flow to maintain the setpoint outlet temperature. .
There is a digital readout on mine that says 120 degrees. Is that the "Set Point" the plumber set? Or just something else?
 

6t7gto

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What I read is factory default is 120*
I think the lowest it will go is 110*
 
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Just installed two Bosch tankless 199k BTU, cascaded. Never looking back. I'm saving so much in electrical and gas! My floor heat will be next!
 

bert79

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There is a digital readout on mine that says 120 degrees. Is that the "Set Point" the plumber set? Or just something else?
Earl, I have two Rinnai tankless 199k btu units that heat the ss and the auto soap passes. I had to flip a dip switch on the inside of each unit to get them up to 120. I think I have the option to go to 140 with another dip switch. Just thinking that your unit may be similar.
 

Earl Weiss

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I think I have the option to go to 140 with another dip switch. Just thinking that your unit may be similar.
If I understand how they work the unit may reduce volume to reach whatever temp you want to achieve. So, having a higher temp is less flow meaning I need to mix in more cold to get enough flow. So, is it a zero sum gain? Higher temp less flow mix in more cold, or lower temp more flow mix in less cold?
 

bert79

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If I understand how they work the unit may reduce volume to reach whatever temp you want to achieve. So, having a higher temp is less flow meaning I need to mix in more cold to get enough flow. So, is it a zero sum gain? Higher temp less flow mix in more cold, or lower temp more flow mix in less cold?
So I have to be honest I did not realize that the tankless reduced flow to achieve the desired temperature before we installed these units. Our plumber was very experienced so we trusted him. He did a wonderful job but was hesitant to put in tankless bc he had bad experiences with them before. I spoke withother local car wash owners before we decided to go that route and they all were very happy with them in similar applications to us.

We have two RL94i units and i found the flow chart on rinnai’s website: https://media.rinnai.us/salsify_asset/s-96094017-ca10-4462-aa5d-e09bb28d2f5d/RL94i (VC2837FFUD-US) SP.pdf?_ga=2.123971852.782950548.1550284409-1749204557.1550284409

I’m currently have them set at 120 and they are heating all the high pressure ss tanks (3) and low pressure ss tanks (3) and the low pressure soap passes on the laser 4000. I know there is a lot of discussion about this on the forum and I certainly dont know if this is the best setup. I do think you are right about what you stated above and as I figure it we have approximately 8 gpm of flow in total from the two units. I could be wrong. This SEEMS to be providing enough flow but I certainly havent been in business long enough to know for sure but for right now it seems fine.
 
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