# Piping diagram for one boiler and two storage tanks



## fhrooter72

I Have a customer who is requesting a second 200gal storage tank next to the current one. They REFUSE to just upgrade to a single larger tank. I have never piped in two tanks with one boiler and have been unable to locate a piping diagram for this. My concern is having two separate Aquastats wired into one boiler. Any ideas?


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## TX MECH PLUMBER

This should be a good one.


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## TX MECH PLUMBER

How about an intro new guy and where in Texas do you work?? Are you a rmp??


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## Tommy plumber

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## fhrooter72

I'm the service manager of a service and repair company in Houston. I've had my MPL for 7 years. Not currently the RPM yet. Did commercial new construction during my apprenticeship, once I got my journeyman I started doing mainly residential service. Get calls from time to time for commercial work.


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## TX MECH PLUMBER

Welcome from abilene. I'm ready to see a two storage tank design. Surly some one will come along with one


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## fhrooter72

Most of my experience is residential but have worked on and replaced single storage tank systems. I asked a good friend who does a lot of commercial boiler work and he said he's never seen it. Evidently a "boiler guy" told my customer this is the way it should be done but he could't do it. I've explained until I was blue in the face that it would be better to install one 500 gallon tank rather than two 200 gallon tanks but he doesn't want to hear it. can this be done and if so how to you run the wiring for the aquastats and would I need a separate circ pump for each tank?


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## theplumbinator

Run boiler supply/return Pipeing as separate zone with its own circulator, & flow check and wire in a separate zone relay, then when second aquastat calls it will have its own loop to heat it up and run independent of the other tank. and the rest of the system.

Then On the domestic twin the tanks together like you would twin two water heaters. hot to hot, cold to cold. Making sure Pipeing is equal length and you put tee exactly in middle of hot and cold lines done. now you will draw equally from both tanks simultaneously. I would also buy the exact same model tank as the existing one if possible. and put in ball valves so you can isolate either tank if one or the other develops an issue. 

Also make sure your existing boiler isn't at max load for btu output and you have a large enough boiler to run a second tank. Thats first on the list before you waste time figuring out how to pipe it. Hope this helps you out.

Sounds like more work than it would be to just install a larger tank. You should work up a price both ways. That many times will help the customer to see the light on what is a better idea. Money is usually a deciding factor. Although you may have to increase the Pipeing sizes if your installing a 300 gal larger tank. Again make sure the existing boiler can handle the larger load with increased tank size. That is still question numero uno no matter witch way you go. Otherwise its also larger boiler time or second boiler time. I want to do this job the more I type the more money im smelling!


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## theplumbinator

Im assuming this is a commercial application? Correct? Doubt anyone needs more than a +200 in residential unless its a multiple family dwelling.


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## fhrooter72

theplumbinator said:


> Im assuming this is a commercial application? Correct? Doubt anyone needs more than a +200 in residential unless its a multiple family dwelling.


:laughing:It's for a lake resort. If it was residential I would just told them to install a tankless.


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## theplumbinator

Yeah I figured it was someplace big. I have installed smaller units into hotels with over 100 rooms lol.


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## TX MECH PLUMBER

theplumbinator said:


> Run boiler supply/return Pipeing as separate zone with its own circulator, & flow check and wire in a separate zone relay, then when second aquastat calls it will have its own loop to heat it up and run independent of the other tank. and the rest of the system.
> 
> Then On the domestic twin the tanks together like you would twin two water heaters. hot to hot, cold to cold. Making sure Pipeing is equal length and you put tee exactly in middle of hot and cold lines done. now you will draw equally from both tanks simultaneously. I would also buy the exact same model tank as the existing one if possible. and put in ball valves so you can isolate either tank if one or the other develops an issue.
> 
> Also make sure your existing boiler isn't at max load for btu output and you have a large enough boiler to run a second tank. Thats first on the list before you waste time figuring out how to pipe it. Hope this helps you out.
> 
> Sounds like more work than it would be to just install a larger tank. You should work up a price both ways. That many times will help the customer to see the light on what is a better idea. Money is usually a deciding factor. Although you may have to increase the Pipeing sizes if your installing a 300 gal larger tank. Again make sure the existing boiler can handle the larger load with increased tank size. That is still question numero uno no matter witch way you go. Otherwise its also larger boiler time or second boiler time. I want to do this job the more I type the more money im smelling!


What's up n a cool iso drawing ???


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## theplumbinator

I dont sit at that drafting table and sharpen my pencils unless im getting paid my bro... maybe one day I will get auto CAD. Not like its new lol I learned it in high school drafting in the 90's im sure its probably changed some since then. But I really like doing my drawings by hand like my old man used to. That job he is doing doesn't need a drawing anyway.


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## Plumbworker

you should only really need one aquastat if everything is piped in parallel you will have even draw and circulation of the tanks as if they were one large tank...


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## bct p&h

Plumbworker said:


> you only need one aquastat if everything is piped in parallel you will have even draw and circulation of the tanks as if they were one large tank...


You think he's going to get an even draw and circulation between a tank that has been in use for who knows how long and a brand new tank? 

If they really want another tank instead of upgrading the current one I would do the boiler piping as a separate loop and run the domestic in parallel with a couple of flow gauges and metering valves to make sure you're getting an even draw out of both tanks.


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## Plumbworker

bct p&h said:


> You think he's going to get an even draw and circulation between a tank that has been in use for who knows how long and a brand new tank?
> 
> If they really want another tank instead of upgrading the current one I would do the boiler piping as a separate loop and run the domestic in parallel with a couple of flow gauges and metering valves to make sure you're getting an even draw out of both tanks.


 i guess i thought he was installing a new system with two new tanks... 

you're scenario is a good idea...


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## bct p&h

Plumbworker said:


> i guess i thought he was installing a new system with two new tanks...
> 
> you're scenario is a good idea...


He wants to install a single larger tank to replace the single 200gal tank that isn't enough for them but they want to just add another tank with the old one. That's probably where the confusion was.


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## TX MECH PLUMBER

theplumbinator said:


> I dont sit at that drafting table and sharpen my pencils unless im getting paid my bro... maybe one day I will get auto CAD. Not like its new lol I learned it in high school drafting in the 90's im sure its probably changed some since then. But I really like doing my drawings by hand like my old man used to. That job he is doing doesn't need a drawing anyway.


I get its not a complex design but I learn better from drawings. I wasn't asking for a true iso. Just a quick sketch but I see ur a bit scared to post some drawing so its ok. Lmao. Jkn. 

I've never used cad. Always on paper and I kinda enjoy drawing so didnt seem like a major request 

Just trying to learn a bit ya know. 

Sounds like a design for a balance hot water system using two heaters but in this case using two storage tanks 

Here's a drawing I did in continuing education class a while back. What can I say I was bored and had asked for a drawing from RJ and he to declined. So I made my own. Y'all dam Yankees are so rude !!!! Lmao


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## theplumbinator

TX MECH PLUMBER said:


> I get its not a complex design but I learn better from drawings. I wasn't asking for a true iso. Just a quick sketch but I see ur a bit scared to post some drawing so its ok. Lmao. Jkn.
> 
> I've never used cad. Always on paper and I kinda enjoy drawing so didnt seem like a major request
> 
> Just trying to learn a bit ya know.
> 
> Sounds like a design for a balance hot water system using two heaters but in this case using two storage tanks
> 
> Here's a drawing I did in continuing education class a while back. What can I say I was bored and had asked for a drawing from RJ and he to declined. So I made my own. Y'all dam Yankees are so rude !!!! Lmao


I can do a quick Rudimentary sketch for you my dude. I got afternoon open tomorrow when I get back to the office to do paper work I can sketch it up quick and post it. Do you have a lot of boilers down that way? Or just see them once in a while? I kinda figured everyone used heat pumps in Texas. U ever get up this far north I will bring you to some boilers you can walk into when we open them. Pretty bad ass stuff. When they get that big they're measured in horse power instead of btu's. Your drawing is very similar to what I'm talking about As far as the domestic. only difference with storage tank would be each tank has a feed and return line going in and out for boiler water two flow checks and to circ pumps. You could add flow control valves also on the domestic to help balance as stated above. But in a perfect world they would be optional. He is adding a new tank in conjunction with a who know how old one.


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## TX MECH PLUMBER

Not many hydronic systems in res but lots of them in commercial Are chillers are bigger down here but we still have boilers. And thanks a sketch would be cool


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## Plumbworker

TX MECH PLUMBER said:


> Not many hydronic systems in res but lots of them in commercial Are chillers are bigger down here but we still have boilers. And thanks a sketch would be cool


were talking a volume open loop boiler right?..... or are we talking indirects?


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## theplumbinator

I m thinking indirects.???? Right????


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## TX MECH PLUMBER

I'm talking open loop boiler systems strictly for heating Around here the heating system and Dom hot water systems are two separate systems I've seen a few lager systems that had steam boilers and used steam heat exchangers to heat domestic hot water these are few and far between like at the hospitals and universities I guess those are a kind of indirect heating systems. But most I've done are open loop for heating and a tankless or 100 gallon com boiler or a boiler with a storage tank for Dom hot water 

I'm not near as educated on hot water systems as y'all of course because of our mild winters 

Last system I did befor I left the mech company was strictly chill water (two trane air cooled chillers ) glycol system and electric heat strips for heating 

Dom hot was point of use tankless heaters 

Here's two pics of some air handlers from that system 
I miss the mech work a lot but make more $ at my new gig 

It still interests me ... That's why I asked for a drawing 

I've never seen heating water in a res application so of course I've never seen radiant floor heating ether. 

If I ever built if want to put it in my house ... At least the bath room


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## Plumbworker

i betcha it's just a open loop volume water heating boiler like a ray pak or something... lol


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## Plumbworker

Around here inspectors frown upon open loop hydronic heat.. There is a major concern about stagnant water and bacteria build up.. they want you to add flow switches, circulator pump exercisers and alarms.. Closed loop is always the safest bet.. i run into alot of system that utilize a water heater as domestic hot water and running space heating for a small infloor zone or something..If you need to use potable hot water as a heat source then a double wall heat exchanger should be used..


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## TX MECH PLUMBER

Plumbworker said:


> Around here inspectors frown upon open loop hydronic heat.. There is a major concern about stagnant water and bacteria build up.. they want you to add flow switches, circulator pump exercisers and alarms.. Closed loop is always the safest bet.. If you need to use potable hot water as a heat source then a double wall heat exchanger should be used..


I don't think I've ever used potable hot as a heat source 

Any hydronic pipe over 2" is usually welded steel. 2" and down is copper

I'd like to see some systems like you describe


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## Plumbworker

generally when someone says open loop it means potable water..


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## TX MECH PLUMBER

Well I guess I used the term wrong. It would be a closed loop cuz the RPZ ?? But not indirect because the the heating water isn't used to heat the hot water ??


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## TX MECH PLUMBER

I'm a j man and have spent most of my days on installation and non on design they have all been engineered by some school boy in penny loafers 

The chill water system in pics above was glycol and had no make up water .. Boss called it a closed loop. So I figured when the system had a make up it would be called an open loop. 

The engineer or some one didnt spec the rite coils and they didnt get the heat transfer they needed so we drained all the glycol in 55 gallon drums flushed the system and installed a RPZ and make up on the system


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## Plumbworker

Yes rpz makes it a closed loop... A tight leak proof hydronic system does not add fresh water to the system on a regular basis the water is dead and stagnant . A indirect water heater uses closed loop hot water from a boiler that flows through a heat exchanger immersed in the tank of potable water therefore the term indirect.

There is also storage type tanks that require open potable water that circulates through a boiler system for volume domestic water heating..


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## theplumbinator

Plumbworker said:


> Around here inspectors frown upon open loop hydronic heat.. There is a major concern about stagnant water and bacteria build up.. they want you to add flow switches, circulator pump exercisers and alarms.. Closed loop is always the safest bet.. i run into alot of system that utilize a water heater as domestic hot water and running space heating for a small infloor zone or something..If you need to use potable hot water as a heat source then a double wall heat exchanger should be used..


Its illegal to use domestic hot water for heating here. So its not something I ever encountered. Ive seen small radiant systems use a water heater, but they have to be rated for space heating and tank and pipe have to be labled non potable. So no one accidentally taps into the tank thinking its domestic. Every heating system here is closed loop with backflow prevention.


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## theplumbinator

Plumbworker said:


> Yes rpz makes it a closed loop... A tight leak proof hydronic system does not add fresh water to the system on a regular basis the water is dead and stagnant . A indirect water heater uses closed loop hot water from a boiler that flows through a heat exchanger immersed in the tank of potable water therefore the term indirect.
> 
> There is also storage type tanks that require open potable water that circulates through a boiler system for volume domestic water heating..


Also indirectly fired. Tank dose not have its own source of heat must use hot water produced by boiler. As aposed to a direct fired heater having its own heat source. Hens the name.


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## redbeardplumber

Plumbworker said:


> generally when someone says open loop it means potable water..


Did not
Know that.


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## benrich07

You can pipe two tanks into one boiler using a reverse return piping system. You can get diagrams online. I am doing that this week. You just have to have a balance tee ( equal distances) between both tank supply outlets.


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## MACPLUMB777

fhrooter72 said:


> Most of my experience is residential but have worked on and replaced single storage tank systems. I asked a good friend who does a lot of commercial boiler work and he said he's never seen it. Evidently a "boiler guy" told my customer this is the way it should be done but he couldn't do it. I've explained until I was blue in the face that it would be better to install one 500 gallon tank rather than two 200 gallon tanks but he doesn't want to hear it. can this be done and if so how to you run the wiring for the aquastats and would I need a separate circ pump for each tank?


*Yes you can do it I have seen up to {4} or more tied together, you get a maximum 3 hour demand window so you do it by storage or a higher BTU boiler check into some of the boiler mfg's websites they should have the drawing and spec's you need, I was trained by A.O.Smith, Laars, and Lochinvar on sizing and how to run multiple tanks, but that was years ago
and I thru away all my books a couple years ago because it is all online today 

and you do not need to worry about the boiler sizing !
it is a matter of time to recover before the next 3 hour demand window 
*


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## shlomy81

This is 1 boiler 399k and 2 200 gal storage piped equally


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## Plumbworker

and i see you got two aquastats wired in their huh..?


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## shlomy81

Just to be on safe side it should one go bad


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