# Tankless & recirc problem



## futz (Sep 17, 2009)

Hey tankless experts. I've made a mistake and need advice.

Just finished a not-too-big custom rancher - two baths in the main house and an attached rental suite at the front (that's the longest run). Slab on grade with underslab waterpipes. It's a bit of a sprawler, like all ranchers. The UG waterlines from mech room to bathroom distribution headers are fairly long. While installing them it didn't occur to me to put in recirc lines because I didn't think they were *that* long.

So I get fixtures installed and fire things up and quickly start to realize that I have a problem. It takes a LONG time to get hot water at the far ends. Partly because of the usual tankless delay, but mostly because it has to warm up all that underground pipe. The customers are quite unhappy.

I dip switched the Rinnai up to 140F, which helped immensely, but it's still quite a wait for hot water.

Is the Taco D'Mand system any good? Would it be the best, or least expensive cure for this thing? Or should I be looking at other options?


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## 504Plumber (Jan 26, 2011)

futz said:


> Hey tankless experts. I've made a mistake and need advice.
> 
> Just finished a not-too-big custom rancher - two baths in the main house and an attached rental suite at the front (that's the longest run). Slab on grade with underslab waterpipes. It's a bit of a sprawler, like all ranchers. The UG waterlines from mech room to bathroom distribution headers are fairly long. While installing them it didn't occur to me to put in recirc lines because I didn't think they were that long.
> 
> ...


I believe the only way to run a recirc pump on a rinnai is off of a small holding tank (5-10 gallon.) I don't have the manual with me but rinnai does have a diagram in their books and I would assume online as well.


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## ZL700 (Dec 8, 2009)

I like the taco remote demand systems, or the metland, both very similar and same taco motor. The remote pump type seems to work best with no return line and it's timed/motion operation maintains warranties with tankless manufacturers intermittent and controlled pump operation requirements without using a external electric tank.

Looking forward to rinnai's newer product coming out soon with pump contacts to operate external pumps. I've heard it will include circulation pump logic to learn usages via flow to control external pump via adaptive intelligent learning. I've also heard Navien will be offering this also soon.


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## GREENPLUM (Jul 27, 2008)

futz said:


> Is the Taco D'Mand system any good? Would it be the best, or least expensive cure for this thing? Or should I be looking at other options?


 
Yes it will fix there problem, those pumps are great and wont effect the warranty of the heater.

Ive installed 20-30 of them ,, all to fix the same probolem your customers have.

http://www.pexuniverse.com/store/category/taco-dmand-system


*Taco 006-DM-PK D-Mand System, Complete w/ plumbing kit, 1/40 HP *Free shipping 

*Taco 006-DM-PK* 

x1​$349.95 / each


*Taco 008-DM-PK D-Mand System, Complete w/ plumbing kit, 1/25 HP *Free shipping 

*Taco 008-DM-PK* 



x1​$405.95 / each


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## [email protected] (Apr 17, 2012)

go to www.rannai.us/documentation/downloads/U287-077x0101.pdf look at page 24 that should answer some questions for you. and ferguson supply offers classes on this every so often you should ask about it it extends thier warrenty if you take it if i remember right because it makes you a certified installer and puts you on there website.


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## [email protected] (Apr 17, 2012)

hmm that didnt take u straight to the page i wanted sry


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## [email protected] (Apr 17, 2012)

hopefully this works


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## AlbacoreShuffle (Aug 28, 2011)

Ive installed the Grundfos Comfort System and had pretty good results.

http://us.grundfos.com/products/find-product/comfort-pumps-up-10.html


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## futz (Sep 17, 2009)

[email protected] said:


> hopefully this works


Oh, that's the way I'd always heard about, with the small electric tank to keep the lines hot. I'd always wondered about the exact way to pipe and control that style of system. Now I know. I don't know why I never saw that pic before though. Looks like it's in the manual. Guess I missed those pages. Thanks for the link. 

BUT... it doesn't apply to my situation. Unfortunately I have *no* recirc return lines installed.

------------------------

Everybody's posts so far are making me feel a good bit more confident in recommending to the GC that we install one or two D'Mand pumps. I'm going to check local pricing and availability on Monday. But I'm still not going to rush into anything just yet.


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## ZL700 (Dec 8, 2009)

AlbacoreShuffle said:


> Ive installed the Grundfos Comfort System and had pretty good results.
> 
> http://us.grundfos.com/products/find-product/comfort-pumps-up-10.html


Through the tankless?

Comfort system is only about .75 gpm , max head 12'

How's that activate a .5 gpm burner requirement with a heat exchanger that has 20' head pressure drop?


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## [email protected] (Apr 17, 2012)

so ill check into the name i cant remeber off hand but i have installed it, there is a fitting that crosses the hot into the cold under a bathroom sink it has check valves so cold cant cross into hot and a small grundfoss pump that u can buy that would be installed on the hot water that pushes the hot water through cold. its different but ive seen it work you should ask your local supply house rep about it he should be able to find it.


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## GREENPLUM (Jul 27, 2008)

[email protected] said:


> so ill check into the name i cant remeber off hand but i have installed it, there is a fitting that crosses the hot into the cold under a bathroom sink it has check valves so cold cant cross into hot and a small grundfoss pump that u can buy that would be installed on the hot water that pushes the hot water through cold. its different but ive seen it work you should ask your local supply house rep about it he should be able to find it.



So,, have you installed that system on a tankless before?

This thread is about tankless


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## [email protected] (Apr 17, 2012)

actually i should have looked through the thread another plumber already posted a link to what i was talking about it was the comfort system. i meant to say it would be something that could be checked in to. call a rannai rep and ask the question.


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## salhb (May 11, 2012)

wouldn't recommend a comfort zone grundfos or watts pump on a tankless, over time will cause the heat exchanger to fail prematurely...better to go metland/taco, their pumps are much stronger, better yet to have a small storage tank also....


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## GREENPLUM (Jul 27, 2008)

[email protected] said:


> go to www.rannai.us/documentation/downloads/U287-077x0101.pdf look at page 24 that should answer some questions for you. and ferguson supply offers classes on this every so often you should ask about it it extends thier warrenty if you take it if i remember right because it makes you a certified installer and puts you on there website.





[email protected] said:


> actually i should have looked through the thread another plumber already posted a link to what i was talking about it was the comfort system. i meant to say it would be something that could be checked in to. call a rannai rep and ask the question.


 
You are spelling it wrong, its Rinnai. That is why your link doesnt work. you musta hand typed that badboy. :laughing:_. _


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## [email protected] (Apr 17, 2012)

oops lol


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## rocksteady (Oct 8, 2008)

I have had a Metlund D'Mand system installed on my house for about 4 years. Mine is installed on a recirc. line though. It has worked great with NO problems. The pump itself is a Taco and it does have plenty of umph to fire the Rinnai. It's a very nice system they have.







Paul


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## ZL700 (Dec 8, 2009)

Comfort pump system from Grundfos wont work on any tankless but a Eternal. All others have too much pressure drop for the little low flow/low head pump to move water through that little wax thermostatic 1/4" hole crossover manifold. Comfort pumps systems were designed for tanks.

A few retrofit reciculation tacos and metlund models work just fine.


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## 504Plumber (Jan 26, 2011)

ZL700 said:


> Comfort pump system from Grundfos wont work on any tankless but a Eternal. All others have too much pressure drop for the little low flow/low head pump to move water through that little wax thermostatic 1/4" hole crossover manifold. Comfort pumps systems were designed for tanks.
> 
> A few retrofit reciculation tacos and metlund models work just fine.


Wouldn't that be the point of rinnai's diagram of putting the pump on a small electric heater instead of on the tankless?


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## GREENPLUM (Jul 27, 2008)

504Plumber said:


> Wouldn't that be the point of rinnai's diagram of putting the pump on a small electric heater instead of on the tankless?


 
yes, if the house already had a recirc line

how would you retrofit it into finished house with no recirc line? 

You dont , you go and buy the Taco Dmand.

Have you ever installed one?


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## pipe wrench ken (Mar 18, 2012)

504, You are 100% correct --I just installed that setup a few days ago. NO MORE PROBLEMS -- HAPPY COSTOMERS


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## GREENPLUM (Jul 27, 2008)

pipe wrench ken said:


> 504, You are 100% correct --I just installed that setup a few days ago. NO MORE PROBLEMS -- HAPPY COSTOMERS


100% correct about what exactly?


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## bizzybeeplumbin (Jul 19, 2011)

In your case you need to circ the hot through the cold line since you do not have the conventional return line. I also highly recommend the metlund system that will connect under the furthest fixture and circ the water through the cold.

warn your customer of one thing, you will get a little warm water at the cold tap when they first run cold after a circulation. use the motion sensors at locations that are traveled often, this way it trips the pump and the thermistor will know f there is hot water. if you use a click button or a remote sensor inside the same furthest bath, it will still take time for the water to complete the circulation. Since metlund has the thermistor built inside it, it will shut down almost right away when hot water is present. There is a popit check valve inside the pump, but if it is installed next to a hose bib, that popit will not stop the hot and cold connection and your customer will get hot water out of the hose bib.

If your customer complains about to much hot in the cold, even with thermistor, and no cross connection, you can dial down the pump using a little screw driver on the circuit board, but you do not want to do this unless you have metlund tech support on the phone with you. I always put in the T2 series under the sinks. remember you need an electrician to put a plug in the cabinet.


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## ZL700 (Dec 8, 2009)

504Plumber said:


> Wouldn't that be the point of rinnai's diagram of putting the pump on a small electric heater instead of on the tankless?


Not without a return line, even with a small tank downstream of the tankless the little pump still has to pump through cold line of tankless first, comfort pump isn't capable of doing that.


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## MikeS (Oct 3, 2011)

[email protected] said:


> hopefully this works


 I recently went to a Rennai training class, and they no longer recommend the storage tank method. They are suggesting the on demand recirc pumps. (sensors when you walk into a bathroom)


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