# Air in hot water system:



## PaulW (Jul 31, 2008)

I have a six floor building with a large boiler system that is creating air in the line on the sixth floor. It has a recirculation system. It currently has two auto air vents but still gets air in the line. Any ideas?


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## MTDUNN (Oct 9, 2011)

PaulW said:


> I have a six floor building with a large boiler system that is creating air in the line on the sixth floor. It has a recirculation system. It currently has two auto air vents but still gets air in the line. Any ideas?


You have roughly 60ft head pressure. It could be a bad auto vent sucking in the air


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## PaulW (Jul 31, 2008)

Thanks for the reply. We have replaced them in fact the director would like to add more. We found a hole in the heat exchanger and thought we had solved the problem but when we isolated the heat exchanger it still pulled air. I believe we have numerous issues with this system one being a crossed line but the air has us baffled.


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## ken53 (Mar 1, 2011)

*boiler*

If your boiler is in the basement, shut down your pumps and check your pressure then do a calculation for head pressure for total height. Now make sure you have at least 6 psi more then your calculated number in the system if you don't when the pumps cut off the auto air vents will suck air back into the system. Also if the expansion tank is water logged it can cause your problem,


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## rjbphd (Feb 5, 2010)

PaulW said:


> I have a six floor building with a large boiler system that is creating air in the line on the sixth floor. It has a recirculation system. It currently has two auto air vents but still gets air in the line. Any ideas?


Is the a heating system or dom hot water system?


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## CTs2p2 (Dec 6, 2011)

I agree on the checking of the boiler pressure..

Why no pics of system?


Need more info..

Is there an auto feed on the system? How bout any leaks? Could be too much fresh water.. Which would also explain heat exchanger failure..

Where are the circs? If on the return they will pull air from the auto vents, and adding more vents won't help.. Unless you want more air 

How are you purging? Not with fresh make up water I hope...

Is there a bladder extrol? Sized right? Right air charge?


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## plumbing ninja (Jan 15, 2012)

Have a look at a brand called Spirovent from Europe. They make a mean as "mans auto air vent" They purge some serious volumes


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## rjbphd (Feb 5, 2010)

First of all.. we don't know if its a heating boiler or water heater as he stated the system have a re circ line... no boiler have it unless its a pressure operator valve.. and another thing, if the boiler is piped properly, you don't need those expensive Spirovent!


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## wyrickmech (Mar 16, 2013)

If it is a heating system shut pumps down and jack the pressure up so the top floor has 10 psi. That should be just enough to show any pinholes in heat exchangers or radiators. Then bleed all air and bump the pumps then bleed again. After several times when you don't have any air at bleeders valve the bleeders off so they cannot suck air.


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## MTDUNN (Oct 9, 2011)

There is air suckage somewhere. I agree to bump it up a little to find the leak


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## rjbphd (Feb 5, 2010)

Where's the OP on this,answering our questions??


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## PaulW (Jul 31, 2008)

Sorry I was working. It is a domestic hot water system. The boilers are on the ground floor. Pump is on ground floor. I am going out this morning to check and take pics and gather more info this is a ten year old building and I have been told they have had issues since day one. I will get more info and post thanks for all the replies!


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## rjbphd (Feb 5, 2010)

PaulW said:


> Sorry I was working. It is a domestic hot water system. The boilers are on the ground floor. Pump is on ground floor. I am going out this morning to check and take pics and gather more info this is a ten year old building and I have been told they have had issues since day one. I will get more info and post thanks for all the replies!


If there's vents on the domestic hot water.. its defenitly piped wrong in first place


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## plumbing ninja (Jan 15, 2012)

There will always be air in the system! It will be released out of solution but this should be small amounts that can build up. if you are experiencing air locks of considerable restrictions then there is a fault somewhere? 
In the words of Sherlock Holmes, "Come, Watson , the game is a foot!"


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## wyrickmech (Mar 16, 2013)

rjbphd said:


> If there's vents on the domestic hot water.. its defenitly piped wrong in first place


there is no heat exchangers either


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## Plumbworker (Oct 23, 2008)

Ok.. so this a dhw? volume water heating boilers feeding storage tanks? Indirects?

I gather you have a recirc line to the tanks as well? 

When you say air in the system is the return pump air locking or is air literally spewing out from the faucets?

I look forward to those pics of the boilers and associated piping and pumps..

As far as air sucking in through automatic air vents thats highly unlikely as long as youre dhw piping does not go negative air cant get in.. domestic systems are usually running aroun 45 - 80psi (check youre pressure on those upper floors!)

Also look at the recirc return piping return water could be going negative due to improper circulator piping and sucking air through a autovent on recirc.. good installing plumbers will put gauges on inlet and outlet of pump to check differential pressure in commercial applications..


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## rjbphd (Feb 5, 2010)

You can get air sucking in if the pump is grossly oversized.. which most are. I have taken out 2" pump and replaced with a tiny 3/4 " pump.. no problem since then.


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## Plumbworker (Oct 23, 2008)

rjbphd said:


> You can get air sucking in if the pump is grossly oversized.. which most are. I have taken out 2" pump and replaced with a tiny 3/4 " pump.. no problem since then.


hmmmm. auto vents cant suck air if the piping is under pressure..oversized pumps in dhw can cause alot of wear and tear and errosion on the piping and excess velocity noise / extra energy comsumption etc but never heard about sucking in air? Splain yo sef..


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## rjbphd (Feb 5, 2010)

Pretty obviously that you don't work on hydronic heating systems..


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## Plumbworker (Oct 23, 2008)

rjbphd said:


> Pretty obviously that you don't work on hydronic heating systems..


of course i do! I'm talking about a dhw system..even with closed loop hydronics air will not suck in unless the piping goes negative sorry thats just physics.. Im not really trying to start anything with you i just cant picture how a oversized circulator would cause air to be sucked in?


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## rjbphd (Feb 5, 2010)

Plumbworker said:


> of course i do! I'm talking about a dhw system..even with closed loop hydronics air will not suck in unless the piping goes negative sorry thats just physics.. Im not really trying to start anything with you i just cant picture how a oversized circulator would cause air to be sucked in?


Pjcture this.. when some or most hot water faucets are opened, the volume of hot water on the supply will handle that.. and with the pump running 24/7.. recirc line get neg nosh and air comes out of solutation. 
If it piped correctly, you don't need vents.. and no pump or small one is all you need for recirc.


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## Plumbworker (Oct 23, 2008)

rjbphd said:


> Pjcture this.. when some or most hot water faucets are opened, the volume of hot water on the supply will handle that.. and with the pump running 24/7.. recirc line get neg nosh and air comes out of solutation.
> If it piped correctly, you don't need vents.. and no pump or small one is all you need for recirc.


Ok i hear ya.. i've never seen that happen.. i've seen many oversized pumps that never cause that issue. 

I'm with you for dhw recirc if designed properly will operate passively without differential pressure induced. also dhw recirc all you want to overcome is the head loss of the piping with very minimal flow rate (smallest circulator possible)..
I also agree that auto vents are only effective on closed loop systems..


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## wyrickmech (Mar 16, 2013)

rjbphd said:


> Pjcture this.. when some or most hot water faucets are opened, the volume of hot water on the supply will handle that.. and with the pump running 24/7.. recirc line get neg nosh and air comes out of solutation. If it piped correctly, you don't need vents.. and no pump or small one is all you need for recirc.


if piped right the recirculating pump only needs to move water at a rate of 5 feet per min. There is no need of air bleeders in a domestic system like you said. If it is domestic system and pump is oversized it could be drawing some air in if the hot is pulled off the recirculating line on the suction side. That would be a long shot. I think it was a heating system he was talking about, large boiler and he said pumps. This indicates lead lag setup, this is not typical on domestic hot water. The indication that there is bleeders also is a good indication of heating. Bleeders here always have a valve below the auto bleeder so you can shut them off so not to suck air even under pressure. The flow of water at high rates past the tap for a bleeder will cause a venture effect. This will cause air to be drawled into the system. Rjbphd is right.


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## redbeardplumber (Dec 4, 2012)

^^^^ I think the OP clarified that it is DHW


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## Plumbworker (Oct 23, 2008)

Ok i get what you guys are saying i have never seen auto vents on domestic recirc.. only closed loop..

This is probably what was confusing me when me was talking abouting about oversized pumps i was not picturing any autovent in the system..

The op needs to get rid of those autovents and install manual block & purge bibs..


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## rjbphd (Feb 5, 2010)

Plumbworker said:


> Ok i get what you guys are saying i have never seen auto vents on domestic recirc.. only closed loop..
> 
> This is probably what was confusing me when me was talking abouting about oversized pumps i was not picturing any autovent in the system..
> 
> The op needs to get rid of those autovents and install manual block & purge bibs..


 Purge bibs??? Wtf?? If you piped it correctly, every faucet on top floor becomes a purge bib!


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## PaulW (Jul 31, 2008)

Still working on the air issue. I have no idea how it was piped. but am reviewing as-built and planning to trace line out. It is a large enough air lock to restrict the hot water flow to faucets. ( meaning low temps) Lines will not purge thru faucets. Problem is with the the hot water recirculation line. Pressure reading on supply side is 45 PSI and 55 PSI on return side big ? there. I am thinking we may have multiple issues here with possibility of a crossed or connected additional line. 

Pic of pump and S tank area:


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## PlungerJockey (Feb 19, 2010)

Cross connection or bad check valve?


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## wyrickmech (Mar 16, 2013)

PaulW said:


> Still working on the air issue. I have no idea how it was piped. but am reviewing as-built and planning to trace line out. It is a large enough air lock to restrict the hot water flow to faucets. ( meaning low temps) Lines will not purge thru faucets. Problem is with the the hot water recirculation line. Pressure reading on supply side is 45 PSI and 55 PSI on return side big ? there. I am thinking we may have multiple issues here with possibility of a crossed or connected additional line. Pic of pump and S tank area:


how long has that pump been in service? Supply 45 and return 55? Pump discharge to the storage tank is lower than the inlet? Is there any arrows for flow on the pump? Has the motor been checked for rotation? Domestic water will not air lock it simply displaces threw the fixtures. Sounds like you have a problem with the pump. Low water temps normally means no flow on recirculating line.


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## Plumbworker (Oct 23, 2008)

rjbphd said:


> Purge bibs??? Wtf?? If you piped it correctly, every faucet on top floor becomes a purge bib!


 In my opinion it's always good practice to install a block and purge even on a dhw return. I usually only use it in the intial comissioning of the system. I agree it is not necessary but i have seen dhw returns lock up circulators even with purging through the fixtures.. makes it easy if youre shutting down a building with recirc then re filling sometimes i dont always have acess to fixtures only a mechanical room so block and purge down stream of the circ guarantees the return is throughly purged of air


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## Plumbworker (Oct 23, 2008)

I'm still not clear on issue the op is having.. other than air is getting into the 6th floor hot water system? more photos of that piping in the mech room would be helpful aswell


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## PaulW (Jul 31, 2008)

It is a huge mech room. Appears to be plumbed good. Pump is fine works the way it should. The pressure readings were from the sixth floor. After I review the as built and trace lines I should have a better understanding of what the heck is going on. This is a hospital so the tracing will not be an easy task they have added to the system all kinds of stuff over the years. There are no circuit setters on sixth floor that I can see but they are on the fourth. Once I narrow down problem or problems I am having the system balanced. This is a ten year old building and has been looked at by numerous other plumbing companies and all kinds of crap thrown at it to try and correct the issue. I was hoping one of my esteemed colleagues here may have come across an identical problem. It would be impossible to diagnosis from pictures and posts. But I do appreciate the ideas! 

Paul


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## wyrickmech (Mar 16, 2013)

PaulW said:


> It is a huge mech room. Appears to be plumbed good. Pump is fine works the way it should. The pressure readings were from the sixth floor. After I review the as built and trace lines I should have a better understanding of what the heck is going on. This is a hospital so the tracing will not be an easy task they have added to the system all kinds of stuff over the years. There are no circuit setters on sixth floor that I can see but they are on the fourth. Once I narrow down problem or problems I am having the system balanced. This is a ten year old building and has been looked at by numerous other plumbing companies and all kinds of crap thrown at it to try and correct the issue. I was hoping one of my esteemed colleagues here may have come across an identical problem. It would be impossible to diagnosis from pictures and posts. But I do appreciate the ideas! Paul


 if it is a hospital I have run into the same problem before. Check every house keeping closet for cross connection at mop sink . It only takes one to cool down the loop. Also you may find a valve shut that will kill the loop. You don't have a air lock you have a cross connection or loss of flow


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## Plumbworker (Oct 23, 2008)

ok im confused youre getting air in the lines or tempered hot water issues?


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## wyrickmech (Mar 16, 2013)

Plumbworker said:


> ok im confused youre getting air in the lines or tempered hot water issues?


what I can gather is that it is cool on the 6th floor that screens cross connection at a bridge faucet or no flow in the loop( valve closed)


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## PaulW (Jul 31, 2008)

After a lot of investigating I think we have narrowed down the problem. It is not air in the line but cold water that is passing thru the sixty Symmons VT112 shower valves. We will be replacing the cartridges to confirm our suspicion.


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## PLUMBER_BILL (Oct 23, 2009)

PaulW said:


> After a lot of investigating I think we have narrowed down the problem. It is not air in the line but cold water that is passing thru the sixty Symmons VT112 shower valves. We will be replacing the cartridges to confirm our suspicion.


*Over the years in commercial buildings 1 fixture has caused temperature problems, that fixture is a T&S faucet with a pre-rinse hose at a disposal sink. Usually the problem is caused by an employee repairing this faucet **and using the wrong barrels [the ones without checks]. When this faucet is in use and the tempeature is set -- both hot and cold open, then the spray is used to operate the faucet. When the spray is closed the biggest cross you ever saw is in place. Enough to cool down all domestic hot water in the rest of the building. *


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## wyrickmech (Mar 16, 2013)

PaulW said:


> After a lot of investigating I think we have narrowed down the problem. It is not air in the line but cold water that is passing thru the sixty Symmons VT112 shower valves. We will be replacing the cartridges to confirm our suspicion.


 yes that would do it. That is a typical bridge point. You might try selling spring checks on branch lines to this type valve


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## PaulW (Jul 31, 2008)

Bill-
That was the very first thing we checked and they do in fact have check cartridges.


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