Air bleed valve installed on a baseboard tee (C) Daniel FriedmanHot Water Radiator Air Bleed Vent Installation Procedures
Diagnostic FAQs on Hot Water Heat Air Bleeders, Air Eliminators & Air Vents

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Air bleeder valves & automatic air purging valve installation procedures: here we explain how & where to install manual or automatic float-type air purgers or air bleed valves on hot water heating system piping, boilers, baseboards, radiators or convectors.

This article series provides a detailed guide to using air bleed valves to get rid of unwanted air in hot water heating systems: fix cold or noisy hot water heating radiators or baseboards.

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How & Where to Install Automatic or Manual Air Bleeder Valves on Hot Water Heating Systems

Baseboard tees with air bleeder installed (C) D FriedmanHow do I add a baseboard Tee bleed valve on hot water heating baseboard piping?

Reader question: Hi Dan, How do I install a manual bleeder valve on my baseboard heating pipe?

Can I tap into the 90 degree elbow with a 1/8 drill bit and sweat a bleeder valve?

Photo at left, a pair of baseboard tees with manual air vent valves.

Are there any other alternatives to incorporate a manual bleeder to the baseboards in the house? - Simon.

Reply: Here is how to buy and install a Heating Baseboard Tee - a special 90 degree elbow that has a reinforced 1/8" NPT tapping and solder it in place at system high points

I was disgusted when a Poughkeepsie plumber we recently hired to install heating baseboard tossed aside the air bleeder fittings I had left to indicate where I wanted them installed.

At above left are the two baseboard tees I had purchased, along with their air bleeder fittings, ready for installation. The plumber (whom I am leaving nameless) left them on the floor - his real reason: he took a shortcut that saved maybe five minutes on the job by using the PEX to copper 90's (with no tapping for an air bleeder valve) that he had on his truck.

When I complained, his retort was that air bleeders are not needed and that they were in his opinion a liability (because he fears they'll leak) rather than an asset. I really wanted to slap him.

Baseboard tee with 1/8 inch tappingWhile it's true that in a perfect world, with a combination of luck, AIR SCOOPS SEPARATORS PURGERS that magically capture 100% of problem air in the heating system, and perfect plumbing routing you can purge air from at least some hot water heating systems at initial installation.

But it's just plain stupid to think that over the life of a hydronic heating system there will never be an air problem in the piping. It's not a perfect world, and "stuff happens", ya know?

So I do not agree with that plumber, nor do heating experts nor the manufacturers who produce a wide variety of valves to manually or automatically purge air from hot water heating systems. As we were installing a new heating loop on an upper floor addition on a one story house, it's likely that air entrained in the heating water or that appears in heating system ever in the future will rush upstairs.

Now I'm going to have to drain down the system and remove his work and install the proper fittings myself.

Photo at left: close-up of a baseboard tee with a manual air purge - note that this valve has not been "installed" yet: there is no thread sealant or teflon tape.

Stop by your local plumbing supplier or
see AIR BLEED VALVE TYPES / SOURCES. The plumbing & heating supplier can sell you a special elbow, a baseboard tee, usually bronze (see our baseboard tee image at left), that solders in place to replace the existing 90 degree elbow at either end of your baseboard run.

The baseboard tee looks like a 90 degree elbow but technically it's "Tee" because it has three openings - the two 3/4" copper pipe fittings and a third 1/8" tapping that is installed pointing "up" to accept the bleeder valve. These are inexpensive fittings, typically around $4.00 U.S.

The baseboard tee or elbow (photo at left) includes a raised casting with additional bronze 1/8" NPT tapping already threaded to accept the bleeder fitting itself. Shown is a sweat-type baseboard tee intended for installation on 3/4" copper hot water heating piping feeding heating baseboards.

Taco air scoop and float type automatic air purge valve (C) Daniel FriedmanAs you will read below, we use teflon tape to seal the threads of the air bleeder when installing it into the baseboard tee fitting.

At the top
of AIR BLEEDER VALVE DIAGNOSTIC FAQs we illustrate a similar air bleeder connecting tee made of cast iron [photo] in use on the heating convector installed in a home built in the 1920's.

Photo at left: a Taco air scoop with an automatic air purge valve on its upper right tapping. This is an effective position for a float type automatic air bleed or purge valve.

And below our next photo shows an older tee-handled air bleeder installed into a baseboard tee on a funky copper baseboard heating run in an older home. Looks a lot like an old automobile radiator drain valve, right? This is probably not a coincidence.

Under a heating baseboard cover, at the start or end of the baseboard run, because of space limitations (under the baseboard cover) and for reliability I prefer to use simple manual bleeder valves at baseboards - they're solid and bullet-proof. Below in this article I show how to install an elegant stainless steel air bleed valve used in these locations.

Baseboard tees are also available for other types of heating piping systems such as PEX tubing, and in mixed sizes such as 1/2" x 1/8" x 1/2" and 1/2" x 1/8" x 3/4" diameters to fit the PEX, bleeder valve, and 3/4" diameter copper baseboard piping

If you are working with standard copper heat piping you probably need one or more 3/4 " x 1/8" x 3/4" baseboard tees.

Heating baseboard tee air bleeder installed (C) D FriedmanWhen I was actually working for a living and had to try to fix air-bound heating baseboards in some older homes it was standard practice to install at least one of these bleeder fittings at the highest point on any baseboard run that was giving problems.

My photo (left) shows another heating baseboard tee with an older type of air bleeder valve installed at a home where there had indeed been a baseboard piping leak. But the leak didn't occur at the air bleed valve, which had been safely shut.

The leak happened when the home lost heat and the piping froze and burst. You can see a section of new copper piping that had been soldered in place during repair work on the home.

You'll want to do he job if adding one or more heating baseboard tees and its air bleeder fitting before the heating season begins so that you won't mind shutting down and cooling off the boiler. You'll need to drain the heating line so that you can de-solder the old elbow and then solder the new baseboard tee in place.

I advise AGAINST drilling and tapping in an air bleeder into an existing elbow even though it's technically possible to do so. The worry is that the 90 is just too thin at the point where you'd drill; even soldering an air bleeder in place I would be forced to agree with my irritating plumber, that in that case the fitting would not be reliable. It's not worth a leak and water damage and mold contamination from a leak that will naturally happen while no one is at home.

Incidentally small amounts of air WILL circulate around through the system as bubbles and can get caught and vented by an air bleeder right at the boiler or its riser pipe. That's why you'll usually find an air bleed in that location. (See our page top photo).

Finally, if you take the annoying plumber's view, you can eschew any air bleeders and instead, wait until the system is air bound and you've lost heat.

Then one can, using boiler drain and feed fittings, force higher pressure through the system to try to blow air out of those uppermost heating baseboards. Of course that' a heck of a lot more trouble than just loosening a bleeder valve screw and letting the air hiss out at the high point(s) in the system.

At AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE we discuss alternative methods for removing air from an air-bound system.

How to Replace the Air Bleeder Valve on Hydronic Heating Systems

If the bleeder valve is completely blocked with debris it might be possible to open it up by completely removing the center screw, but as I warn in a companion article
at AIR BLEED VALVE LEAK REPAIR, on a hot heating system, trying to get the screw back in while being squirted by hot water can be unpleasant. I've done this once or twice, but generally you will probably have to replace the entire valve.

Hot water heat air bleed valve preparation with teflon tape (C) Daniel Friedman Hot water heat air bleed valve preparation with teflon tape (C) Daniel Friedman

Watch out: if replacing an entire air bleed valve or even if just removing its inner screw, the task is safer and less messy if performed when the heating system water is cool or cold.

To keep heat on after removing a leaky bleed valve to prepare for replacement, that is, in a pinch, you can remove the old air bleed valve and temporarily close the opening where it was mounted using a threaded pipe plug of the proper size (usually 1/8" NPT) while you hitchhike off in subzero weather to buy the replacement part. I would prefer to just show up with the replacement part in hand to do the whole job at once. Just sayin'

To install a new air bleed valve into an existing threaded opening on a radiator or baseboard tee we do not have to disassemble it, but we should use a thread sealant. I prefer teflon tape or teflon paste.

Wrap the teflon tape onto the threaded portion of the bleeder valve as I show at above left. I am turning the valve in the clockwise or "screw-in" direction. This will wrap the teflon tape in the right direction onto the treaded valve base.

At above right you can see the finished result - sort-of. If an idiot installs the bleeder valve with its inlet opening blocked by teflon tape (below left) the valve will not work. At below right you can see that I have cleaned off the excess teflon tape that would have blocked the air bleed valve inlet opening.

Hot water heat air bleed valve preparation with teflon tape (C) Daniel Friedman Hot water heat air bleed valve preparation with teflon tape (C) Daniel Friedman

Air bleed valve installed on a baseboard tee (C) Daniel Friedman

At left you can see the new air bleeder valve with it's teflon tape seal screwed into the 1/8" NPT of a baseboard tee fitting.

For the photos shown here I used new parts at a workbench.

But in the field may be installing this air bleeder into a pre-existing tapped opening, probably working in the dark, upside down, in a cold, tight crawl space, alone, maybe with the company of spiders and snakes - which is no place for an air bleeder that should be easy to access if it is to ever be used.

Watch out: For automatic or float type air bleed valves, the replacement procedure is essentially the same as shown here. Take off the old valve, seal the threads on the new bleeder valve, and screw it in place.

But take care not to use the float body itself to screw the float bleeder valve into position - you may break it.

Use a wrench in place on the cast portion of the valve base intended for that purpose.

Watch out: for automatic and some manual air vents to work properly the vent or valve has to be installed in a location that will receive air in the water piping system, radiator, or other device, has to be installed in the proper position (some vents like the Sparco air purger and the Taco 409 Air Vent work properly only in the upright position), and the pressure in the heating (or cooling water) system must be higher than atmospheric pressure.

Otherwise when the vent or valve is opened air may enter the piping system rather than being purged from it.

Watch out: when installing canister type air eliminators or air purge valves such as all of the float type valves, do not try to screw the valve body tightly into the receiving plumbing tapping by using a tool to torque or twist the valve body - you will most likely damage or ruin the valve.

Valves such as the Maid-o-Mist copper body units shown at left (Maid-o-Mist No. 71 Auto-Vent) are turned by hand only - notice the clue: there is no faceted fitting designed to accept a wrench on some models; other air vent valves do include a fitting that can accept a wrench, such as the Maid-O-Mist No. 74.

Tips for Replacing a Damaged or Leaky Air Bleeder or Vent on Hot Water Heating Systems with a Minimum of Water Leakage, Spills, Mess or Panic

Installation Questions & Answers about Hot Water Heating System Air Purgers & Air Bleeder Valves

Question: Where to Install extra air bleeder valves: Advice for installing remote or secondary air bleeder valves

When installing an automatic air bleeder on a system is it possible to install a tee at the high point then run a line to a different location and install the auto air bleeder in the secondary location, and will it work if that secondary location is lower than the tee in the main line? - Steve

Reply: the high point air bleeder valves are most important on hydronic heating systems but air bleeders in other locations work also

Steve you will sometimes see automatic air bleed valves at various heights and locations on heating system piping, and all of them will work to release air that finds its way to each of those locations. However it's most likely most important to include an air bleeder at the highest point in system piping where air may be found.

You can run a tee at a high point, as in your question, and then add a more remote air bleeder, provided that all of the piping slopes horizontally or better, uphill from the tee.

Small amounts of air in a hydronic heating systems are sometimes pushed around by the circulating water and may reach even lower air bleeders. But the circulator can't push large amounts of air - the system can become air bound unless means are provided for getting rid of it.


For eliminating air from potable water, cold water or hot water supply systems see AIR ELIMINATORS for POTABLE WATER SUPPLIES

Question: Installing air bleeder valves: Is it ok to install an air bleeder valve by just drilling and soldering into an existing copper pipe elbow on the heating line?

Hi Dan,
I've hired a HAVC guy to put replacement slant-fin baseboard heaters. because some of the stubs are coming from the wall, he claimed that he can't install a regular bleeder but have to drill a hole on the elbow and solder one in place. Is this the right way to do it? thanks. - Lily

Reply: not recommended


My OPINION is that drilling and soldering a bleeder valve into an existing copper elbow is an unreliable "fix" to add an air bleeder - the risk is that the soldered fitting is not strong enough and that you have a leak, worst when no one is home - and a flooded building and costly repairs.

Drilling a standard copper or bronze elbow to try to tap in a 1/8" diameter vent is likely to lead to leaks and maybe costly damage to building later on.

If it were my house I'd cut away the wall and solder the necessary fittings (called a baseboard tee and illustrated at the top of this page) in place, or I'd look a second time to see if there is not another location that will do.

Question: Installing air bleeder valves: which end of the heating baseboard gets the air bleed valve

Should the air vents be installed on the inlet or outlet of the baseboard heater? - Ron Thompson

Reply: at the outlet end or at both ends of the baseboard

Ron, if I were installing only one manual air bleed valve I'd certainly place it at the end of the heating baseboard so that I could force air out of that baseboard section.

On difficult or long baseboard runs I like to install bleed valves at both ends of the baseboard run. In that case I might install an automatic air bleed valve at the input end of the baseboard and a manual air bleed valve at the end of that baseboard run. In that manner, as long as the automatic air purge or air bleed valve keeps working air shouldn't enter the baseboard run.

But if air does get into the system, from a bad valve or from a sudden large surge of air, some of which gets past the front end air bleed valve, I can still purge the problem air from the system without having to follow other more complicated, lengthy, and expensive procedures.

Question: installing heating piping air bleeder valves: do I need air bleed valves at both ends of the piping run?

My home has several zones with base board hot water radiator. the problem zone is divided by a stair case between two rooms. The plumber installed no bleeds. he simply made a 90 degree rise 7 feet to the top of the landing then across 10 feet to 90 degree 7 foot drop to the other room. This makes the 7 foot stair case landing the highest point for this zone. I now have an air lock. Do I put a bleeder valve on both the right and left side of the landing? (PS. .I am now very proficient at complex copper sweating.) Is there a rule dictating how short or long a run need to be before needing to add 2 bleeders.


Melvin, I don't think you need two bleeders if you can get one at the end of that high point in the piping - by "end point" I mean that for that high horizontal run, put a bleeder at the end of the run (where the pipe heads back down) that is more distant from the boiler feed side. That is, it's on the "return" end of that high leg.

Then with the bleeder in place, when the system is up to operating temperature and pressure, if you open the bleeder, the system pressure should push the air out.

Recapping: I like bleeders at both ends of high runs myself, but in truth you should be ok with just a bleeder at the far end from the feed side of the boiler.

Let us know how it goes - the results will help other readers.

Follow-up comment:

A [lumber friend came by said the same thing you said Dan. However, we both feel sometimes saving $6.00 costs hundreds or thousands. So we ended up just placing bleeders at both ends of the high point. I tested your theory by filling the system and only bleeding system using the valve installed at the return side bleed and the system worked.

So thanks very much for your help.

Reply: plumber shortcuts on heating piping diameter and air bleeder valves cost plenty later

I agree with you completely. The owners and contractor were disgusted when Paul A., somewhat of a bully plumber in Poughkeepsie, saved himself some labor time and "saved" the customer essentially nothing by installing smaller diameter hot water heat supply piping to and from a building addition.

Paul also saved himself labor time by refusing to install two air bleeders on the high loop in the system even though we bought the bleeders and left them on the floor at the locations where they were to be installed. When questioned he explained that "half-inch heating piping is just fine, and you don't want those bleeders anyway - they're a liability - they always leak".

The smaller heat supply piping he used failed to consider the design specifications for the heating system - an assumed hot heating water flow rate through the baseboard, combined with a high-output heating baseboard design had permitted the use of about half the normal linear footage of baseboard in the room. Now if the heat is found to be inadequate the owners will have to either ruin their design by adding baseboard, or they'll have to rip out ceilings to install larger diameter heating water piping.

And about leaving off those air bleeders: sooner or later over the life of the building, when that high heating pipe loop becomes airbound, the occupants will have to hire a heating or plumbing tech to go through a more troublesome (and costly) procedure to fix the airbound heat problem. If Paul had taken the trouble to make a first-class installation, one could have just opened a screw and bled out the air in minutes.

Question: Does the air eliminator at the boiler mean I don't need vents at the baseboards?

Does a Spirovent™ eliminate the need for baseboard vents? - plw65 11/18/11


No. While an automatic air eliminator at the heating boiler will usually avoid an airbound heating system, leaks or work on the heating system or even bacterial growth can cause air accumulation along heat piping runs, particularly in longer horizontal runs without much pitch.

We usually need at least one air bleed valve at the high end of the heating piping, and we often need to add a bleed valve to remove air from tricky or long baseboard or piping runs. You can install a new system with no air bleeders involved, and the heating system may work perfectly for many years. But sooner or later the system will need air purging.

A properly located manual air bleeder makes this job quick and trivial. Without it there are still ways to fix the problem


but with more trouble and at a greater cost.

Question: I want to shorten a 24-inch air bleeder valve

I have a bleeder valve that is 24 inches tall and would like to shorten it to 12 inches. Can a plumber specializing in hot water heating do this job or do you advise against? Thank you - Thierry Neubert 4/20/12


Theirry I'm not sure it's safe for us to diagnose and prescribe for your heating system with so little specific detail. In general you're talking about a simple plumbing job, changing out a length of pipe for a shorter one. But check with your heating service technician to be sure that there is no specific need for a 24-inch tall riser pipe.

Question: what about adding air vents at baseboards - is that a good idea? What about using Sharkbites for fittings?

I noticed that you said automatic air bleeders are typically installed at or near the boiler/expansion tank and that you only mention manual set ups at the baseboard. Do you advise against installing automatic air bleeders at the baseboard? Second, my install is nearly all pex, have you found a source for 3/4" pex x 3/4" pex x 1/8" female npt tees? I've ben unlucky thus far. Finally, I'm planning on using sharkbite push/fit connections anywhere possible, they max out at 200 degrees, while my system will generally be about 170 degrees. Do you advise against using sharkbites in this application? - Bobbito 1/23/13



I like to install manual air vents (automatic ones are nice but I've seen a few leak complaints) at the highest run of heating baseboard as well as at the start or more often the end of any runs of baseboard with a history of becoming air bound.

We have used sharkbite type fittings on heating systems as well as PEX tubing with no problems, operating at 180F.

Question: how do I add an air vent if there is no room for a vertical pipe at the boiler

how install auto air vent if no 18 inches horizontal pipe possible? - Air Vent Installation 3/31/2013



I've seen people try drilling, tapping, soldering, gluing an air vent right into a pipe - that's not a reliable plumbing connection and I DO NOT recommend it.

I DO advise installing air bleeders at some critical baseboard locations, especially if there has been a history of particular hot water baseboard sections becoming air bound.

If I didn't have a specific problem hydronic heat baseboard section I would still like to see an air bleeder vent installed at the start or end of the highest baseboard section in the building or on each heating loop.

There are automatic air bleeders that work unattended, but because some have reported leaks at those devices you might install a manually operated bleeder at the baseboard start or end elbow - the necessary fittings are a completely common part available at all plumbing and HVAC suppliers.

Question: what is the proper installation position for float-type automatic air bleeder valves: do we mount the air vent or air eliminator valve vertically, horizontally, or what?

Float type air bleeder valve installed horizontally (C) InspectAPedia BLI’ve read your site for years and enjoyed it immensely. You probably get a zillion questions but I have one I can’t find anywhere anywhere, including your site.

I have 1965 hot water heating and at the point farthest from my furnace is a Taco 400-2 air vent.

The weird thing is its installed horizontally. It's screwed into the end of the pipe.

Will the valve still function sideways or is it only designed to be vertical?

Might be moot as its not the highest point anyway, but I’m interested if it does anything at all.

Thanks. - B.L. 11/30/2013

Reply: float type valves depend on vertical positioning for proper float operation - install the float type air vent according to the manufacturer's instructions, which in all our literature means "upright" with the cap loose

Float type air bleeder vent installed properly (C) Daniel FriedmanAbout that vent, I'm pretty sure that's a conventional float-type air vent; if so it can't work properly for long in that position - since the floats depend on gravity and on air moving to the float top to work properly.

There are, of course, other types of air bleeder vents that can be installed horizontally, including some shown earlier in this article.

I'd bet that the valve stem cap on the float type air vent in your photo (above left) is screwed shut - or if it's not, and if it was not leaking, the orifice may have been clogged by mineral deposits and heating water debris.

Our photo at left shows a typical float type automatic air bleeder valve on a hydronic heating system.

It is installed upright, and [click to enlarge] you can see the warning tag about leaving the cap loose if the float vent is to actually release air from the heating system.

Really? Well not always. There are some hydronic heating system auto vents such as the Maid-O-Misty No. 66, 67, 68 Auto-Vents (below left) that are float operated vents that do not require an air chamber, and some models such as No. 27 and No. 37 Auto-Vents that are mounted horizontally (below right), as we illustrate just below. You can get a clue about whether or not the air vent is intended to be mounted horizontally or vertically just by looking at it, though reading the installation instructions is really more sensible. [Click to enlarge any image]

Maid-O-Mist No. 67 automatic air vent is vertically mounted Maid-O-Mist No. 67 automatic air vent is vertically mounted

Taco 409 Air vent schematic Taking a look at the product specification sheets for Taco's float type automatic air vents such as the Taco 409 shown at left, as well as having disassembled a few of them myself makes clear that for proper operation the device depends on free movement of a float-operated vent valve inside the device.

The float moves "up and down" as air enters or is vented from the device. The device wants to be installed vertically. At left is a schematic for the Taco 409 Air Vent, adapted from the company's product literature.

Watch out: when installing an air vent, Taco warns as follows:

Please note that when installing a new system or retro- fitting an old, you must flush out the disturbed dirt as well as any oily film or solder paste entrained in the system water.

If this is not done, it is entirely possible that the internal float mechanism will become clogged open, causing the air vent to leak.

For installations where pos- sible property damage may occur due to fluid leaking from the vent, a 3 ⁄ 4 " ID hose may be clamped to the air vent outlet. The hose may then be fed to a drain or col- lection area designed for the fluid in use. DO NOT USE A SOLDER CONNECTION AT THE OUTLET! - Taco High Pressure Vent Instruction Sheet (2007)

You can contact Taco directly for assistance (I found that the company's product specification sheets easy to download but those documents don't include installation details) at

Taco 417 Vent positionsHow did it happen that a vertical float valve found itself swimming horizontally on a heating system pipe? If I'm correct I suspect that previously there was a manual air bleed valve in the location in your photo - not a particularly good spot anyway. Perhaps someone thought "I can improve this mess, I'll just install an automatic float valve in this spot and I won't have to keep fooling with this valve."

One can imagine that the whole idea was not very successful.

At left we illustrate another air bleeder that could have been installed horizontally in the location of the float vent in your photo. This is a Taco 417 Vent or "coin vent" suitable to replace the valve in your photo. The Taco 417 can be installed in the three positions shown, and is operated by hand - no tools are necessary. In the proper position it can vent air automatically from the heating system.

About our articles, while I'm glad they have been helpful to you and much appreciate the comment, let me emphasize that questions are very welcome. We would much appreciate hearing any comments, critique, suggestions, or further questions that you may have about any of our diagnosis/repair articles.


Continue reading at AIR BLEED VALVE LEAK REPAIR or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see AIR ELIMINATORS for POTABLE WATER SUPPLIES to remove air from water supply systems, piping, fixtures.


Or see these

Radiator Air Bleeder & Vent Articles

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