Where should an air separator be located?
June 15, 2015

Where should an air separator be located?

The best place to locate an air separator in a hydronic system is where the water temperature is high and the pressure is low. The solubility of the dissolved gases in the water is lowest at these conditions. For a heating system, the ideal location is at the outlet of the heat source. For chilled water systems, locate the separator in the return to the chiller. In wall-hung boiler installations, it is convenient to mount the air separator in the vertical hot water supply pipe, as shown in the figure below.

 

Of course, not all jobsite piping arrangements allow ideal installation of the air separator. Remember, an air separator is a multi-pass device and over time it will "scrub out" air and can bring the dissolved air content down to less than 0.5% of system volume. In that condition, the water will provide excellent heat transfer (air is an insulator, not a good conductor), and virtually eliminate noise (air makes noise in a hydronic system). Also, and maybe most important, removing air reduces corrosion. Corrosion destroys moving parts such as valve packings and pump seals and will foul heat exchangers, all bad news.

An air separator is cheap insurance against premature system failures and unhappy customers; read more about air separation (and dirt separation) in Caleffi idronics issue #15. Also, check out the whole family of Caleffi 551 Series DISCAL air separators and 546 Series DISCALDIRT air/dirt separators. Contact us with any questions you have; we are glad to help you succeed!

Blog post comments
Eugene
September 20, 2017

can the air separator be installed below the level of the pipe? that is level of the pipe is at 3m from floor then pipe goes to the air separator inlet at level 0.5 m from floor, out to the separator outlet at the same level then up again to pipe original level of 3 m. Can this be done? what is the disadvantage?

Thank you.
Eugene

tech_support
September 29, 2017

Of course an air separator should be mounted where it will be most effective, in the boiler supply piping, on the low pressure side of a pump, and preferably at a high point in the system where the air will tend to be. The separator will remove whatever air passes through it, no matter where it is located in the system, so you can mount is as you describe but it may be less effective.

BT
April 03, 2018

How is the efficience of air separator at inlet of chilled water pump compared with air vent (air release valve) installed at several high level location of piping system?

Regards,

BT

Anonymous
April 05, 2018

Air vents should be mounted at any point in a piping system where an air bubble could form. An air separator is an in-line device that removes entrained air (microbubbles) that is moving with the flow of the fluid; they are different products for different purposes and you can't really compare efficiency between the two. All hydronic systems should have air vents (wherever needed) and an air separator.

Jose Parra
November 13, 2019

If I must install the air vents at the point with higher temperature and lowest pressure, could I install the air vents near to pump suction in order to substitute the air separator?

dan_firkus

In reply to by Jose Parra

November 13, 2019

Jose,
The air vent would typically be installed at the highest point because it is counting on air to migrate into the vent, raise the float and is then removed. The air separator on the other hand is installed at the suction side of the pump because the coalescing mesh will separate the air bubbles from the water as it is drawn through the separator allow them to rise to the top of the and be removed. Without the mesh or something to separate the micro-bubbles the air vent would not be as effective.

Dan Firkus
Caleffi North America

Bruce

In reply to by dan_firkus

October 05, 2020

Dan,

Our system circulator is downstream of the boilers. The 2 mid efficiency boilers each have a pump. Would it be better to put the air separator before the main circulator, where the water is coolest though, or after the boilers, and all the pumps, where the pressure is relatively higher?

dan_firkus

In reply to by Bruce

October 29, 2020

Bruce, You will want to locate the air separator on the supply side of your boiler wihere the temperature is the highest and on the suction side of your pump.

Bruce

In reply to by dan_firkus

October 29, 2020

Right, that's what's not possible. The suction side of the pump is on the return side. The hot water is on the supply side. Which is more important, low pressure or high temperature - if we have to choose?

dan_firkus

In reply to by Bruce

November 02, 2020

Bruce,  See attachment.  The separator at the supply out of the boiler where water temp is the highest and the pump on the return pumping through the boiler still locates the separator on the suction side of the pump so that is an acceptable installation.
 

Zoka Zola
December 22, 2019

There seems to be a discrepancy between the text above "the best place to locate an air separator in a hydronic system is where the water temperature is high and the pressure is low" and the diagram above. The diagram shows the air separator at the high pressure location - after the pump. Can you please clarify.

Our intent is to install air separator in this sequence: boiler, expansion tank with air filler and drain, air separator and then circulator. Can you please comment.

dan_firkus

In reply to by Zoka Zola

December 23, 2019

Hello, your location of the air separator and pump is correct, you would want your air separator before the pump or on the suction side of the pump. The fill and expansion tank can be installed below the air separator on a smaller system or on a larger system we see them installed on the return side. The photo above shows the air separator on the supply side and the pump on the return pumping throught the boiler. The boiler provides the pressure drop which will place the air separator on the low pressure side with the pump after it pulling through the separator.

Steve

In reply to by dan_firkus

September 02, 2022

So Caleffi always recommends their air separator on the suction side of a pump?

dan_firkus

In reply to by Steve

September 07, 2022

Steve, When locating the expansion tank on bottom of the separator you will want to have the pump after the separator pumping away so you do not preload your expansion tank. The air separator has a large body that provides a good drop in velocity that allows the internal coalescing mesh to separate the microbubbles from the water. It will perform better with the pump downstream from the separator.

Dan
January 03, 2020

Underfloor heating with a boiler how many automatic air vent valve can I install and best location
thanks
Dan

dan_firkus

In reply to by Dan

March 02, 2020

Dan,
You can install multiple auto air vents into a system and they are usually installed at a highpoint in the system or the top of a riser.

Greg
February 28, 2020

My hot water circulation system is used more as a cold water purge system. User hits a button and a pump runs for about a minute for that section of the house. I have four pumps each at the end of a dedicated return from the four corners of the house. All four pumps then return water through a manifold to a single pipe to the hot water heater. I don't really want to buy four air separators to place at the suction of each pump and I'm wondering if there's any point in putting it on the single return line to the cold inlet of the water heater which I can make the highest point in the system. I really don't have a particular issue without the air separator but want to put one in for good measure and to eliminate any air after servicing and purging the system.

dan_firkus
March 02, 2020

Greg,
It sounds like you may be working with domestic hot water. We do not have a separator available for use with that application. We do have our PlumbVent that low lead for a domestic water heating application, but that is an air vent not an air separator. If you need more information or want us to look at the details on your project you can email our tech support at techsupport.us@caleffi.com.

Thank you,
Dan Firkus

Nick
May 14, 2020

does it matter how close the air separator is to my pump.

dan_firkus

In reply to by Nick

May 15, 2020

Nick, When locating your air separator it is important to have it located on the outlet side of your boiler and suction side of the pump. The pump can be directly after the air separator. For air separation I would recommend our 551 Discal.   You can also find more information on hydraulic, air, dirt and magnet separation in issue 15 of our Idronics or in our Coffee with Caleffi webinar.

eric baum
November 17, 2020

Can one utilize two air separators? The pump is inside my Baxi Luna boiler- can I put an air separator on both the outgoing water line and the return water line?
And install Both of them above the level of the boiler (at the ceiling height) ?

dan_firkus

In reply to by eric baum

November 19, 2020

Eric, Typically you would install one air separator and that would be located on the supply out of the boiler and on the suction side of the pump.  You will want to varify but looking at the Baxi Luna boiler the internal pump appears to be on the return side pumping through the boiler.  If you are piping this primary/secondary, the air separator could be located on the secondary circuit, supply before the pump.   You could locate a second air vent at a high point in the system for additional air removal.

Richard
January 06, 2021

What causes water to leak out of an air vent? And, how do you prevent the water leak in the air vent in the future?

dan_firkus

In reply to by Richard

January 07, 2021

Richard, Typically when water leaks from the air vent it is a sign that there is debris that has passed the flow and become lodged in the seat of the needle valve that allows air to escape. You may be able to remove the cover and float and clean that out. If you need, Caleffi offers a replacement cap and float. Our products are the most serviceable in the industry.

brian
January 26, 2021

I've seen where an expansion tank is plumbed directly to the bottom port of an air separator. Doesn't the element in the air separator function similar to that in a dirt separator? What prevents dirt in the fluid stream from dropping out at the air separator element and entering the expansion tank? Thanks.

dan_firkus

In reply to by brian

February 04, 2021

Brian, The smaller brass air separators are ok to pipe the expansion below the unit. The larger steel models we do not recommend using that location to pipe the expansion tank too. If you have a really dirty system than I would not recommend that location for the expansion tank because the air separator could remove dirt into the expansion tank. The idea with the expansion tank and fill located below is because it is installed at a point of no pressure in the system.

dan_firkus

In reply to by brian

February 04, 2021

Brian, The smaller brass air separators are ok to pipe the expansion below the unit. The larger steel models we do not recommend using that location to pipe the expansion tank too. If you have a really dirty system than I would not recommend that location for the expansion tank because the air separator could remove dirt into the expansion tank. The idea with the expansion tank and fill located below is because it is installed at a point of no pressure in the system.

Kasia
November 14, 2022

Our heating system is not working, it is a 3 storey house and heating only works at the top floor. We were advised a power flush and after the boiler was put to max all radiators but one were working. After that there’s a discharge from an overflow pipe and we switched off the heating. After we turned it on, we discovered that one of the radiators in the bedroom upstairs stopped working and other ones in the lower 2 floors don’t work either. We are advised by a plumber to remove the air separator. Where is the separator located? Is it somewhere in the wall so they would need to open the wall?

dan_firkus
November 16, 2022

It sounds like there could be a lot of air in the system that is causing flow issues and heat transfer. The discharge from the overflow when the system temperature was turned up could be a sign of thermal expansion or an expansion tank issue. It sounds like an air issue in the system a good air separator may be needed.

Eleanor Elliott
November 28, 2022

I live in an apartment 12th floor end unit. My heat goes off every 2nd day due to air blockage they say. They don't know what is wrong and are getting angry. What should I do?

dan_firkus

In reply to by Eleanor Elliott

November 29, 2022

Eleanor, Air typically will rise to the highest point in the system and separates from the water easier as it is heated. Identifying how the air is getting into the system is important. There is always oxygen in water. I would recommend a good system air separator and possibly air vents at the high point in the system. If there is that much air in the system a good flush and fill followed up by air separation and vents should correct this.

Jeff
December 30, 2022

If installing an air separator on a wall hung closed loop boiler system do I still need to bleed the lines to purge any air in them or will this eliminate that step? I'm in the process of replacing my 18yr old wall hung boiler with a new one. Figured I'd install a separator while I'm replacing the boiler. Was curious if using one eliminates having to bleed the lines. Appreciate the help

tech_support

In reply to by Jeff

March 21, 2023

Jeff, you should still purge your lines on initial fill and startup. The air separator will remove the entrained air over the following weeks as the system is up and running.

Paul Neufeld
January 21, 2023

I noticed in a comment above that an air separator is not designed to work in a hydronic system where the hot water is heated by a hot water tank (conventional domestic electric hot water heater). Is that correct? If I have read this correctly, is there a product you can recommend that helps to get rid of microbubbles in my system which uses a hot water heater?

tech_support

In reply to by Paul Neufeld

March 21, 2023

Paul, air separators are designed to work in a closed loop hydronic system, and not a domestic water system. They are not made of low lead brass, and therefore cannot be installed on the domestic side. If you are having trouble with air trapped in your domestic system, you could install our Plumbvent at high points in your system, as it is the only low lead automatic air vent on the market.