# Calculate this and you are "The Man"!!!



## jrplumbing74 (Apr 19, 2009)

Job I'm reworking for a builder where plumber had installed 2 Rinnai R75LS tankless units set at 130. Circulation loop thru Grundfos 3 speed pump thru a State 10 gallon electric tank. The loop including return is 280' long. It is 3/4" pex piping uninsulated. Tank has 1650 watt element. Cannot get loop to produce over 90 degree water. Incoming water temp is 64 deg. If you can tell me why this WON'T WORK, and why, I'd say you know your stuff.......enjoy and Merry Christmas.


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## easttexasplumb (Oct 13, 2010)

Is the elect waterheater plugged in and operating correctly. When recirculating tankless through a storage tank, heat loss will occur. I would insulate the return line, help prevent heat loss, and make sure the elect water heater is working, maybe install higher watt element.


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## Phat Cat (Apr 1, 2009)

It was made in Mexico?


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## Associated Plum (Nov 4, 2008)

I would also check if the water is mixing thorugh a solenoid or single handle faucet


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## RealLivePlumber (Jun 22, 2008)

Considering the pipe itself holds about 6 gallons of water, and there is no insulation on it...................:whistling2:


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## Tommy plumber (Feb 19, 2010)

280 feet away? Why is it located so far? The closer the w/h to the point of use, the better.


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## plumbpro (Mar 10, 2010)

RealLivePlumber said:


> Considering the pipe itself holds about 6 gallons of water, and there is no insulation on it...................:whistling2:


Maybe I'm reading the original post wrong. It said he has 280' total of 3/4 insulated pex. I think the whole line including return is insulated.


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## OldSchool (Jan 30, 2010)

What is the GPM of the circ pump on high speed..... you may be over your GPM of the instant tank.... try lowering the pump speed


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## plumbpro (Mar 10, 2010)

plumbpro said:


> Maybe I'm reading the original post wrong. It said he has 280' total of 3/4 insulated pex. I think the whole line including return is insulated.


never mind I re read, it is uninsulated. I would definately insulate the line, you are probrably losing a lot of heat there, and definately check the pumps rating. Like OS said, it could be moving to fast and not allowing the water to heat.


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## jrplumbing74 (Apr 19, 2009)

Yes the total length of the entire hot loop is 280. 
"State" water heaters aren't made in Mexico.....
True loop systems have no branches to fixtures. Supply runs thru all fixtures and returns to pump.
Rinnai warranty requires recirculation loop to NOT run thru tankless units.(I thought everybody knew this???)
Pump running at 15 gpm.
Hints:
Calculate--
Btu loss per hour per foot on pex...
Kilowatts needed to retain btu loss based on gpm and temperature rise.


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## OldSchool (Jan 30, 2010)

maybe you shoud have draw a picture of what you were trying to do because your description was the ****Z


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## SewerRatz (Apr 25, 2009)

jrplumbing74 said:


> *"State" water heaters aren't made in Mexico.....*


But the label you posted clearly says Made In Mexico


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## Redwood (Sep 8, 2008)

SewerRatz said:


> But the label you posted clearly says Made In Mexico


It sure do...


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## luv2plumb (Apr 30, 2010)

Redwood said:


> It sure do...


 
Maybe he read it that the label was made in Mexico but the heater was made in the USA


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## easttexasplumb (Oct 13, 2010)

I belive State is a sister company of A.O Smith. To the best of knowledge the bulk of their heaters are make in mexico. Some models are made in Ashland, Tenn.


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## ZL700 (Dec 8, 2009)

"Job I'm reworking for a builder where plumber had installed 2 Rinnai R75LS tankless units set at 130. Circulation loop thru Grundfos 3 speed pump thru a State 10 gallon electric tank. The loop including return is 280' long. It is 3/4" pex piping uninsulated. Tank has 1650 watt element. Cannot get loop to produce over 90 degree water. Incoming water temp is 64 deg."

You obviously know the answer-(I Think)

First its probably immaterial what the incoming water temp is since if you piped it correctly and per Rinnai recommendations. New fresh water introduced into the DHW system piping and recirc must enter the Rinnai units first. However if fixture draw is below .4 or .5 GPM or a small leak or water trickle has occurred in the system, the unit(s) never fire thus it is introduced into the small electric tank that its main purpose besides decoupling the recirculation from the Rinnai units is to heat/reheat the recirc water and storage via the electric element (silly wasteful concept that it is).

With 280' of a basic PEX radiant loop since it's uninsulated, losing up to 20 BTU's per foot, more or less, depending on how much surface contact the piping has. A 1650 watt element (120v I assume) will only generate about 5,500 BTU's, which is just a bit more than the heat loss of the pipe, thus the difficulty in maintaining the electric heated recirc loop. 

Remember your probably not raising the temp from cold inlet to 90, but room temp or space temp that pipe is located in, so if its 70 to 90 its a 20 dt which explains the close match of element BTU and pipe loss. 

15 GPM on 280' of 3/4" PEX with fittings? I seriously doubt that, if we had the real GPM rate we could really do some calcs.


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## Titan Plumbing (Oct 8, 2009)

Ooops.........reading is fundamental.


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## Protech (Sep 22, 2008)

:yes:



ZL700 said:


> "Job I'm reworking for a builder where plumber had installed 2 Rinnai R75LS tankless units set at 130. Circulation loop thru Grundfos 3 speed pump thru a State 10 gallon electric tank. The loop including return is 280' long. It is 3/4" pex piping uninsulated. Tank has 1650 watt element. Cannot get loop to produce over 90 degree water. Incoming water temp is 64 deg."
> 
> You obviously know the answer-(I Think)
> 
> ...


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## RealLivePlumber (Jun 22, 2008)

jrplumbing74 said:


> Yes the total length of the entire hot loop is 280.
> "State" water heaters aren't made in Mexico.....
> True loop systems have no branches to fixtures. Supply runs thru all fixtures and returns to pump.
> Rinnai warranty requires recirculation loop to NOT run thru tankless units.(I thought everybody knew this???)
> ...


I see you are giving us some "hints". And you thought everyone knew it anyway. I did not know it was a fugging quiz.
Thought you needed help with a problem. So, since you don't, have a nice day. or not.


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## jrplumbing74 (Apr 19, 2009)

Wow...what a bunch of aholes. To zl100: nice job. All the others with stupid comments further justify why: #1- Confronted with a problem that takes a little math and research, your knee jerk reaction is to resort to elementary immature behavior. Not surprised by this on the forum as of late. 
Basically this was meant to be an exercise showing the ineffectiveness of poor planning. This packaged system was sold by Ferguson Enterprises with the only concern being the warranty and not the proper operation of system. I hadn't reached my final conclusion till spending over 4 hours on the phone with State (they said unit was assembled in Texas) and Rinnai (the best technical support I've ever seen).
From my calculations the element wattage has to be over 2.25 kilowatts to operate correctly and I will be insulating the lines today.


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## ZL700 (Dec 8, 2009)

jrplumbing74 said:


> Wow...what a bunch of aholes. To zl100: nice job. All the others with stupid comments further justify why: #1- Confronted with a problem that takes a little math and research, your knee jerk reaction is to resort to elementary immature behavior. Not surprised by this on the forum as of late.
> Basically this was meant to be an exercise showing the ineffectiveness of poor planning. This packaged system was sold by Ferguson Enterprises with the only concern being the warranty and not the proper operation of system. I hadn't reached my final conclusion till spending over 4 hours on the phone with State (they said unit was assembled in Texas) and Rinnai (the best technical support I've ever seen).
> From my calculations the element wattage has to be over 2.25 kilowatts to operate correctly and I will be insulating the lines today.


 
4+ hours? it should have been obvious in 5 minutes or less what the issues were

I'm thinking your first post you were clueless, after wasting countless wasted hours investigating you had an idea for the second post.

Besides, since when hasnt it been standard practice to insulate lines that are recirculated?????


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## ILPlumber (Jun 17, 2008)

Ferg prolly did sell a packaged unit. ON THE ASSUMPTION THAT THE INSTALLING PLUMBER WOULD INSULATE THE LINE.

Also, Seems to me the tankless would work much better if it's not around the F'ing block from the fixtures. 

Any savings you have by installing a tankless have to be eaten up by that little water heater. 

I bet the crawlspace stays nice and toasty.

Poor design and a poorer install..

Lest we not forget we have seen your other work. I don't know why anyone is surprised by this.....

Yours truly,
one of the aholes


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## Plumbdog (Jan 27, 2009)

Ok. Maybe its just me , but I think the OP was trying actually add something to the forum. So to rip him for not knowing where the WH was made or pics of previous work or anything not really pertaining to the post seems a bit lame.


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## ZL700 (Dec 8, 2009)

Big panties worn here


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## jrplumbing74 (Apr 19, 2009)

Matt, as I noted in initial posting, I didn't do the install. Took it over from other plumber who went under. 
It's funny to me that the original posting was meant in good faith but for some reason has turned into a big F.U. festival. I joined this forum thinking that it would be a good opportunity to learn, gain advice and share with other peers in my field. I think in all actuality that I'm the big Ahole for joining a group of what appears to be worn down, pissed off at the world, close minded, has beens, that would rather sit around ***xx ******x each other at their own "I'm a better plumber than you..." convention then having something positive to contribute.


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## jrplumbing74 (Apr 19, 2009)

ZL700 said:


> 4+ hours? it should have been obvious in 5 minutes or less what the issues were
> 
> I'm thinking your first post you were clueless, after wasting countless wasted hours investigating you had an idea for the second post.
> 
> Besides, since when hasnt it been standard practice to insulate lines that are recirculated?????


 The 4+ hrs also included resetting the altitude switches (over 2200' at job), piping off condensation tubing that hadn't been done resulting in having to clean out both combustion chambers. Also rewired Honeywell 1006 aquastat that was wired backwards originally, causing pump to run 24/7 and continuity check on tank element. 
All of which I'm most assured would've taken you much less time to do, but "you've all seen my work" so I thought I would take my time and try to do things right for a change.


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## ILPlumber (Jun 17, 2008)

jrplumbing74 said:


> Matt, as I noted in initial posting, I didn't do the install. Took it over from other plumber who went under.
> It's funny to me that the original posting was meant in good faith but for some reason has turned into a big F.U. festival. I joined this forum thinking that it would be a good opportunity to learn, gain advice and share with other peers in my field. I think in all actuality that I'm the big Ahole for joining a group of what appears to be worn down, pissed off at the world, close minded, has beens, that would rather sit around ***xx ******x each other at their own "I'm a better plumber than you..." convention then having something positive to contribute.


Not an FU festival. I'm not a worn down, closed minded, pissed, has been plumber. 

I am a plumber who knows what he is doing. 

You have come off as a plumber who doesn't know what he is doing from the get-go. 

I apologize. I didn't realize I had to take you by the hand and spoonfeed you the advice you needed on the rather obvious problem you faced. 

If you re-read your first post. You will notice, if the answer was a snake, it woulda bit ya.

Good day


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## Plumbus (Aug 4, 2008)

To get back to the issue of this thread; 
Jon
Did insulating the line result in any appreciable increase in temp of the loop?
BTW:
Does anyone have heat loss calcs on field insulated 3/4" pex? I guess you'd have to take into account the quality of the insulation job.


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## jrplumbing74 (Apr 19, 2009)

Matt said:


> Not an FU festival. I'm not a worn down, closed minded, pissed, has been plumber.
> 
> I am a plumber who knows what he is doing.
> 
> ...


What did I just say.....once again Mr. Moderator Matt you have proven my point. Nobody is as good as you...ok...I get it....I suck...my work sucks... I've been doing this on my own for half my life and haven't learned a damn thing. 
I have accreditations and take every class from every manufacturer and codes dept I can to keep up and work 60+ hrs a week running a plumbing co. that puts food on the table for 6 employees and their families. But I wouldn't think for a minute that I know or am any better than you or any other. My father is a lifetime plumber for 54 years and at the age of 72 he told me "Learn 1 new thing everyday because the minute you think you know it all, plumbing will teach you a knew lesson." 
You might notice at the end of my initial post I wished all of you a merry christmas. For you Matt, I think you need it. Happy Holidays.


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## jrplumbing74 (Apr 19, 2009)

Plumbus said:


> To get back to the issue of this thread;
> Jon
> Did insulating the line result in any appreciable increase in temp of the loop?
> BTW:
> Does anyone have heat loss calcs on field insulated 3/4" pex? I guess you'd have to take into account the quality of the insulation job.


Yes it did. We installed R Value Rated 6 insulation today using glue seal on all closures. We weren't able to insulate piping in walls behind drywall. Upon completion I was able to achieve 110 degrees after cycling pump for 1 hr.


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## jrplumbing74 (Apr 19, 2009)

3/4 pex preinsulated from wirsbo claims 8.0 btu/ hr at 70 degrees.


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## ZL700 (Dec 8, 2009)

And In the end, will the builder learn not to hire the lowest price plumber? I know you said you didn't do the job, but I'd be quick to point out to the builders he got what he paid for; problems.


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## Protech (Sep 22, 2008)

70 degrees what? ambient vs watertemp? heat loss depends on temperature differential.




jrplumbing74 said:


> 3/4 pex preinsulated from wirsbo claims 8.0 btu/ hr at 70 degrees.


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## jrplumbing74 (Apr 19, 2009)

Protech said:


> 70 degrees what? ambient vs watertemp? heat loss depends on temperature differential.


70 degrees Delta T mean anything??? It doesn't to me but that's all I've got in book.


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## Protech (Sep 22, 2008)

Ya, that's the same thing. delta T = differential 



jrplumbing74 said:


> 70 degrees Delta T mean anything??? It doesn't to me but that's all I've got in book.


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## Plumbus (Aug 4, 2008)

The manufacturer's heat loss calc on 3/4" Pre-_insulated_ AquaPEX®
is 8.0 BTU/h/ft2 (at 70° Delta T). If the exterior surface area of 1 linear foot of 3/4" pex pipe is aprox. 33 sq in, then it's heat loss is about 1.833 btu/hr, assuming a)the od of pex is .875" and b) that the job applied insulation is as efficient as that from the factory.
The ∆ T, or difference in temperature refers to the disparity in temperature between the fluid inside the pipe and the ambient temperature outside the pipe. And, the greater the disparity (∆ T), the greater the heat loss. In this case, we know the temp within the insulated pex (110° F) after one hour of run time. If we knew the ambient temperature during that run time and the temp of the water inside the pex at the start of the cycle, it might help us understand mathematically why Jon's insulated pex was able to reach 110° F by the end of the one hour cycle.


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## Lifer (Nov 23, 2010)

Plumbus said:


> The manufacturer's heat loss calc on 3/4" Pre-_insulated_ AquaPEX®
> is 8.0 BTU/h/ft2 (at 70° Delta T). If the exterior surface area of 1 linear foot of 3/4" pex pipe is aprox. 33 sq in, then it's heat loss is about 1.833 btu/hr, assuming a)the od of pex is .875" and b) that the job applied insulation is as efficient as that from the factory.
> The ∆ T, or difference in temperature refers to the disparity in temperature between the fluid inside the pipe and the ambient temperature outside the pipe. And, the greater the disparity (∆ T), the greater the heat loss. In this case, we know the temp within the insulated pex (110° F) after one hour of run time. If we knew the ambient temperature during that run time and the temp of the water inside the pex at the start of the cycle, it might help us understand mathematically why Jon's insulated pex was able to reach 110° F in during the one hour cycle.


I was gonna say that .. He stole my answer ..:thumbup:


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## jrplumbing74 (Apr 19, 2009)

Ambient air temp was 65 deg. Incoming water temp was 64 at initial stone cold start up.


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## user2090 (Sep 26, 2009)

Don't see what the big deal is, just follow this simple formula in the picture below, and you good to go.


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## Cal (Jun 17, 2008)

Guess I got here late and Indie stole my answer ,,,


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