# Linked Tankless



## spudwrench (Sep 15, 2009)

O.K., found from my previous post that the "Hybrids" pretty much suck.
So, as an example, If you link 2-5GPM tankless do you initially get 10 GPM output of flow? Reduced to maybe 8 during the long cycle?
This is dedicated to a custom shower with a max. flow of 7.5 GPM.
Any takers on this? So far, none of the tankless websites give me much info 
about linking. What do you think? The owner wants long showers, but can't tell me how long. ????


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## ZL700 (Dec 8, 2009)

spudwrench said:


> O.K., found from my previous post that the "Hybrids" pretty much suck.
> So, as an example, If you link 2-5GPM tankless do you initially get 10 GPM output of flow? Reduced to maybe 8 during the long cycle?
> This is dedicated to a custom shower with a max. flow of 7.5 GPM.
> Any takers on this? So far, none of the tankless websites give me much info
> about linking. What do you think? The owner wants long showers, but can't tell me how long. ????


I don't understand what you mean by long cycle? Only thing besides the model chosen to refuse flow is reduction in gas inlet, inlet pressure reduction or drop in inlet temp requiring higher temp rise. 

A BTU can raise one pound of water 1 degree blah, blah, blah, so depending on flow requirement along with temp rise, you get the units GPM capability. 

Yes linking the units together by theory will double the flow on like models providing that you have the distribution piping to carry the gpm along with adequate inlet pressure to overcome pressure drop and distribution friction.


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## MikeS (Oct 3, 2011)

spudwrench said:


> O.K., found from my previous post that the "Hybrids" pretty much suck.
> So, as an example, If you link 2-5GPM tankless do you initially get 10 GPM output of flow? Reduced to maybe 8 during the long cycle?
> This is dedicated to a custom shower with a max. flow of 7.5 GPM.
> Any takers on this? So far, none of the tankless websites give me much info
> about linking. What do you think? The owner wants long showers, but can't tell me how long. ????


 haha, I thought this was the benefit of tankless, endless supply of hot water. I'm guessing this shower uses more than a single tankless can supply? I have no idea to your answer, because I personally think tankless water heaters are for ****. But a good tanked 50 gal. water heater, no problem.


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## ZL700 (Dec 8, 2009)

MikeS said:


> haha, I thought this was the benefit of tankless, endless supply of hot water. I'm guessing this shower uses more than a single tankless can supply? I have no idea to your answer, because I personally think tankless water heaters are for ****. But a good tanked 50 gal. water heater, no problem.


Bring yourself up to speed of modernism

At 10 GPM that's a 4 minute shower at best with your 50 gal tank and everything else gets cold for awhile afterward. 

If your in business to make money educate yourself on products and options and give your customer what they want, or they will go elsewhere forever.


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## MikeS (Oct 3, 2011)

ZL700 said:


> Bring yourself up to speed of modernism
> 
> At 10 GPM that's a 4 minute shower at best with your 50 gal tank and everything else gets cold for awhile afterward.
> 
> If your in business to make money educate yourself on products and options and give your customer what they want, or they will go elsewhere forever.


well. this guy needs apparently more than one. And for one, I have a 50 gal water heater, and I can take 30 minute showers, so your numbers are false. Tankless is a Euro joke, in my opinion, but go ahead, sell em all you want. To each his own.


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## easttexasplumb (Oct 13, 2010)

http://www.wholesaletankless.com/connect-cable-p-70.html


Rinnai tankless water heaters can be linked together, both units will run at same time.


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## ZL700 (Dec 8, 2009)

MikeS said:


> well. this guy needs apparently more than one. And for one, I have a 50 gal water heater, and I can take 30 minute showers, so your numbers are false. Tankless is a Euro joke, in my opinion, but go ahead, sell em all you want. To each his own.


His 10 GPM shower is not your 1 GPM shower

30 minutes with a 1 GPM shower head perhaps, do the math with your 50 gallons.
Continuous non-stop flow it's 80% of tank capacity available.

Dont expect you would know that either

I bet your single 50 gallon tanks will magically fill a 100 gallon soaker tub too!


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## MikeS (Oct 3, 2011)

ZL700 said:


> His 10 GPM shower is not your 1 GPM shower
> 
> 30 minutes with a 1 GPM shower head perhaps, do the math with your 50 gallons.
> Continuous non-stop flow it's 80% of tank capacity available.
> ...


 its 2.5 gallons a minute. And like I said, I thought the advantage to a tankless was unlimited supply of water. Well, it is, at so many gpm's per minute. Who the hell uses 10 gallons a minute? Whatever, sell him three.


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## ZL700 (Dec 8, 2009)

easttexasplumb said:


> http://www.wholesaletankless.com/connect-cable-p-70.html
> 
> 
> Rinnai tankless water heaters can be linked together, both units will run at same time.


Hence the post title- "linked tankless"


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## MikeS (Oct 3, 2011)

ZL700 said:


> His 10 GPM shower is not your 1 GPM shower
> 
> 30 minutes with a 1 GPM shower head perhaps, do the math with your 50 gallons.
> Continuous non-stop flow it's 80% of tank capacity available.
> ...


 also, even though a 50 galln tank has about a 35k btu burner, it still does have a recovery rate. so yes, I suspect it would fill a 100 gallon horse trough.


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## ZL700 (Dec 8, 2009)

MikeS said:


> its 2.5 gallons a minute. And like I said, I thought the advantage to a tankless was unlimited supply of water. Well, it is, at so many gpm's per minute. Who the hell uses 10 gallons a minute? Whatever, sell him three.


Very true, unlimited "endless hot water" but at what GPM to you want it? 

People with nice homes want 10 GPM these are the people that pay the $$$$


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## MikeS (Oct 3, 2011)

ZL700 said:


> Very true, unlimited "endless hot water" but at what GPM to you want it?
> 
> People with nice homes want 10 GPM these are the people that pay the $$$$


regardless, its limited to 2.5 gallons a minute in CA. These things just don't justify the cost to upgrade.


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## spudwrench (Sep 15, 2009)

Guess I was clear as mud. Custom shower=multiple body [email protected] each. That is where the GPM# comes from. Long cycle means as the inlet water is cooler (winter) the tankless will slow the flow to achieve the desired temp. rise. And linked is indeed both operating at once. Just exploring all options to give a spoiled customer what they want. Thanks for the input. Just trying to learn something here.


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## ZL700 (Dec 8, 2009)

spudwrench said:


> Guess I was clear as mud. Custom shower=multiple body [email protected] each. That is where the GPM# comes from. Long cycle means as the inlet water is cooler (winter) the tankless will slow the flow to achieve the desired temp. rise. And linked is indeed both operating at once. Just exploring all options to give a spoiled customer what they want. Thanks for the input. Just trying to learn something here.


Understood, many will explain the slight depreciation in flow during winter months, and end user may be willing to accept versus spend more on meters, piping, units. 

It's their money not yours, give them what they want and smile all the way to the bank.

I'll never understand a contractor that will talk a customer out of what they wanted all while reducing their income over it. In the end, customers after thoughts are, but I wanted it.


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## ZL700 (Dec 8, 2009)

MikeS said:


> regardless, its limited to 2.5 gallons a minute in CA. These things just don't justify the cost to upgrade.


That's 2.5 GPM per head or nozzle in California. Nothing stops you from having 4 heads in the shower, thus 10 GPM. 

That loop hole DOE was looking to close this past spring and was shutdown.


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## Pipe Rat (Apr 5, 2009)

A 4 minute shower huh? HA HA I guess your taking full temp showers of 120 degrees? That math is flawed :whistling2:


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## 504Plumber (Jan 26, 2011)

We have linked heaters in the past, installed 2 rinnai in a very small house before because the owner wanted to be able to run every single faucet in his house without a pressure drop. We did it to make him happy and it worked well. If you install a 9.4gpm heater and had a 10gpm shower all it would do would drop pressure to keep up with the demand. 

I would pay you money if you could fill a 100 gallon soaker with a standard 50 gallon heater and have the same temp the whole time.

I don't understand these days someone saying a tankless is smoke and mirrors and a "European joke." Are you for real?


I will have to say, we pulled a very old (early 1900's) gas fired heater out of a house and I was shocked to see a primitive style heat exchanger inside.


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## ZL700 (Dec 8, 2009)

Pipe Rat said:


> A 4 minute shower huh? HA HA I guess your taking full temp showers of 120 degrees? That math is flawed :whistling2:


Directed at me since I posted something about 4 minutes?

At 10 GPM was the discussion wise guy

105 degree shower, stored at 120, 2.5 GPM flow, less than 13% mixed, plus mixed tank temp slide, you do the math, I rounded it at 4 minutes. 

HA HA yourself


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## ZL700 (Dec 8, 2009)

"I would pay you money if you could fill a 100 gallon soaker with a standard 50 gallon heater and have the same temp the whole time."

MikeS seems to think that recovery will cover that 

504- that 9.4 heater you reference is at a 30 degree rise, 50 inlet + 30 is a 80 degree shower, too cold for me.


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## 504Plumber (Jan 26, 2011)

ZL700 said:


> "I would pay you money if you could fill a 100 gallon soaker with a standard 50 gallon heater and have the same temp the whole time."
> 
> MikeS seems to think that recovery will cover that
> 
> 504- that 9.4 heater you reference is at a 30 degree rise, 50 inlet + 30 is a 80 degree shower, too cold for me.


Not down here, I would be shocked if our water was even at 60• for more than a day or two. Tankless are great, as long as you don't live in Alaska or other mostly cold climates. At 9.4 that is a 30• rise but what at 5 or 7? With 2 linked heaters you are still going to get desired temps.


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## ZL700 (Dec 8, 2009)

504Plumber said:


> Not down here, I would be shocked if our water was even at 60• for more than a day or two. Tankless are great, as long as you don't live in Alaska or other mostly cold climates. At 9.4 that is a 30• rise but what at 5 or 7? Wi th 2 linked heaters you are still going to get desired temps.


I do know your above ground storage can chill that water down 2.5 months a year. 
Your nights right now are down to 32 degrees


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## 504Plumber (Jan 26, 2011)

ZL700 said:


> I do know your above ground storage can chill that water down 2.5 months a year.
> Your nights right now are down to 32 degrees



Look at it this way, a 30 degree rise for 9.4gpm. With 50 degree water you are still getting 4.5-5 gpm with a 75 degree rise. That is not too bad, for large homes with showers that require more flow in a colder climate it would make sense to link two heaters together. Two linked heaters would still get you to ~10gpm with a 75 degree rise. ~8gpm with 100 degree rise, thats not too shabby. Our nights are barely in the 30's, sure the initial burst of water is cold, I can gaurantee sometime next week we will have lows back into the 60's.

That is all to maintain 120-125 degree water.


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## ZL700 (Dec 8, 2009)

504Plumber said:


> Look at it this way, a 30 degree rise for 9.4gpm. With 50 degree water you are still getting 4.5-5 gpm with a 75 degree rise. That is not too bad, for large homes with showers that require more flow in a colder climate it would make sense to link two heaters together. Two linked heaters would still get you to ~10gpm with a 75 degree rise. ~8gpm with 100 degree rise, thats not too shabby. Our nights are barely in the 30's, sure the initial burst of water is cold, I can gaurantee sometime next week we will have lows back into the 60's.
> 
> That is all to maintain 120-125 degree water.


Not arguing I just know your water gets cold too part of the year. 
I have a place south of Houston, warmer than you and the water gets cold in Jan & Feb.

199,000 / 8.34 / 60 / 75 x .84% = 4.45 GPM


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## Greenguy (Jan 22, 2011)

With the tankless you can still use a 60 gallon storage tank(or any size you want), it may allow you to get away with not needing a second unit. Keep the tank temp maxed out and a thermostatic valve on the outlet side.


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