Steam vents on heating systems:

Here we provide an inspection and repair guide to the vents found on radiators and piping used with Steam Heating Systems.

We explain one pipe and two pipe steam heating vents and how they work, and the article includes diagnostic and repair advice for hissing sounds at steam radiators, steam vents that don't close when they should, steam vents that don't open when they should, noisy steam vents, and steam vent leaking or spitting.

We describe how to identify, service, or repair steam radiator air vents. How to regulate heat using air vents on steam radiators & troubleshooting steam heating system radiator vents & controls. How do we know if the steam vent is working on a radiator?

Guide to Steam Vents on Residential Heating Systems

These questions and answers about choosing, installing, troubleshooting, or replacing steam vents on steam heating systems were posted originally at STEAM VENTS - home - you will want to read the diagnostic advice given there/

Our photo (above left) shows a common model of automatic air bleed valve used on residential steam heat radiators.

[Click to enlarge any image]

On 2018-11-18 1 by (mod) - How do you know when a steam vent is defective

Thanks for a great question, Herman.

A bad steam vent can fail by

1. Not venting air at the start of a heat on cycle - radiator stays cold

2 Not closing when the raduator is hot - radiator gets hot but never stops ventinh steam all during the heat-on cycle

3. Leaking

On 2018-11-16 by Herman

How do you know when a steam vent is defective

On 2018-06-02 S.Tieger plumbing said: reporters don't report steam accidents properly

[edited to remove inappropriate language - Ed.]

I was called as an expert witness relating to the two children burned to death in Hunts point section of the bronx

All the news media lied as some said "high pressure steam" or posted more [incorrect and inappropriately scary terms like] "radiator exploding"

The news media is... scaring people who have steam systems thinking their rads are ready to EXPLODE

...

Installed of asking someone actually in the profession they make up news as if it is gospel

On 2018-01-05 by (mod) - possible risk of steam burns or more-serious injuries

Watch out: Since you cannot turn off the radiator as it has no working control valve, and if the steam vent blows steam continuously (needing replacement)

The risk is a serious steam burn. Keep peopl e away, especially children.

You can reduce the steam plume size by tossing a towel over the vent. Do not try to remove, touch, nor break off the vent. That would be very dangerous.

Contact your landlord as this is an unsafe condition.

On 2018-01-05 by linda

Hello. My radiator in my NYC apartment, the turn on and off valve has always been broken and the nozzle blows water, sometimes a river. The nozzle is continuously changed by super but it still leaks water. Today, for the first time, the nozzle is blowing steam. I burned my hand checking it. Is this dangerous?

An emergency? Today is Saturday and the super will not come until Monday. As I said, I cannot turn the radiator off as the valve has always been broken. Thank you.

On 2017-12-06 by (mod) - can I make a steam vent totally quiet?

Without a vent to allow the steam to push the air out of a convector or radiator it's not going to get very hot.

On 2017-12-05 by Patrick

I have two questions

We have a two pipe steam heating system. Should every convector have a steam vent?
and

is there a way to quite a steam vent?

We had two convectors in our bedroom. the heating company removed/capped them off because of how loud they are.

However, my concern is that we could be getting better or more heat if we had them on and are able to quite them in some manner.
Thanks

On 2017-12-04 14:09:03.948077 by (mod) -

John,

The problem you describe of uneven heat distribution in a building with steam or hot water heat is a common one. For Steam Heat systems the problem of a too cold room at the end of the steam heating line is usually corrected by improving the steam pipe venting system. The technician may install a vent near your heated area that vents air out of the system faster.

It's also possible to fine tune heat distribution by adjusting individual radiator valves (closing valves part way in too-hot areas) and by choice of the steam vents (faster or slower) used on individual radiators.

On 2017-12-03 05:12:57.267345 by John

I have a question i live in a apt building and in a one pipe steam system i am the last apt on the steam line while the first apt going nuts because of too much heat i get heat but much later all my valves are brand new and all the vents are also hoffman brand new how is this can be fixed? Thank you

On 2017-05-01 22:21:50.600756 by Anonymous

On 2017-04-29 01:48:55.201522 by (mod) -

Sounds as if the windows lack a storm window and are very cold; Keeping windows open of course increases the heating cost;

If the steam vents are closing when they should I'd focus on the windows themselves. Leaks, and missing storms.

On 2017-04-28 23:53:53.564211 by GJ

I have a newer steam boiler for three flat building.
On the second floor, during winter, a good amount of water accumulates on front wall from baseboards up to windows.

First I changed radiator vents. But that did not help.

I fixed windows so that they remain slightly open to circulate air. That did not help.

I tilted radiators but did not help.

I do not see any water on the ceiling at first floor.

Water turns in to molds which I keep cleaning and re-painting three to four times during winter season.
Can you suggest how to solve the problem?

On 2017-02-24 16:53:49.781103 by (mod) -

Last baseboard? steam baseboards? I'm confused.

On 2017-02-24 13:33:13.805447 by Tom C.

top floor of 2 Family Home New boiler 1yr. old steam. the last baseboard on the run no heat the 2 before spray water upon start up.No cut offs .Need help

On 2017-01-31 17:44:18.718489 by (mod) -

Patty,

If water is leaking out of a steam radiator at its steam vent it sounds to me as if the radiator's condensate is not draining back into the condensate return line - if so that blockage needs repair.

As you'll read in the article above, once the radiator is hot the steam vent should close, as venting air from the steam radiator should no longer be necessary. So if the vent hisses the entire time the steam system is on, and if the radiator is hot, then the vent is not working properly and needs repair or replacement.

The "not close against water" is ok for a vent used on a radiator.

On 2017-01-31 17:41:30.986466 by (mod) -

Patty said:
Hi, I have a one pipe steam heating system in a small house built in the early 1900’s. It feeds 5 radiators in the house. It has a main vent hat I do not think came with the original installation. It is a Dole No.4. Quick Vent, see page 3 of the valve flyer located on this webpage ...

It is described as follows: For Mains. Does not close against water, ¾ “ male, ½ “ female connection.

Our problem is that it leaks water when the system starts up. The radiators are all heating, the system does make noise but mostly just hissing.

We aren’t sure if this is the right valve for the system? If there is a problem with the valve, or if there is something else going on. When should a one pipe system have a valve that “does not close against water”?

On 2017-01-15 15:23:27.197015 by (mod) -

Jason, something is rotten in the state of Radiators at your house.

Look, the steam vent is somewhere above the middle height of the radiator, right? For a radiator to be filling up with condensate and filling up the valve the condensate return piping or outlet from that radiator must be totally blocked.

If you're handy and if you can let the system cool off so you don't get burned, (and heat is off for a time) you may need to remove and clean or replace a radiator steam trap or outlet at the radiator base.

Let me know if that works for you.

On 2017-01-15 13:50:25.660892 by Jason

I have a steam system and one of my radiators (the largest in my house and closest to boiler) stops working due to the air release valve filling with water. Originally I thought I didn't have enough pitch on the radiator so I placed a few more shims under the air release end. That didn't work so I put a new air release valve in and that didn't work either. If I take the valve out and dump the water out it will work until it fills back up, which is only 1 heating cycle. Any advice what I could check next?

On 2017-01-13 01:11:15.273536 by (mod) -

Bill:

There could be rust or debris clogging the radiator condensate exit.

Also search InspectApedia for BANGING STEAM PIPES for more detail

On 2017-01-12 20:40:48.577955 by Bill

New Weil maclain sgo3 boiler installed in nov. Last radiator on system banging and leaking water from newly installed vent rite #1 vent. Radiator is shimmed to aid condensate removal but all has failed.

On 2016-12-17 17:46:04.193271 by (mod) -

Please see the diagnostic and repair suggestions for COLD RADIATORS in this article: COLD HOT WATER RADIATOR or BASEBOARD

On 2016-12-15 17:54:34.956012 by jlesser969

All radiators in my 1910s house have Durst 1/8" Adjustable Angle Steam Radiator Vent Air Valves. The air valve on the radiator furthest from the gas boiler heats up, but puts out so much steam that the wall above and behind the radiator drips water. I've adjusted the opening on the valve but it doesn't change the water running down the wall. Do I have a defective valve?

On 2016-12-15 15:44:56.144843 by Jimmy

I have a steam heat radiator that is cold an leaks water. I tilted the radiator so the water flows back away from the air vent. What's next.

On 2016-12-10 12:51:40.881401 by (mod) -

Paul:
It might be possible, in some steam piping arrangements, to remove vents from radiators - such as piping that allows air to leave at the top of a radiator when steam rises at the bottom. In most steam radiator arrangements found in residential properties, simply removing a steam vent stops air from exiting the radiator and thus keeps steam from entering it: the radiator won't get hot.

You will also see steam vents removed from radiators that are on a heating system that has been converted from steam to hydronic (hot water) heat.

On 2016-12-09 20:32:28.099920 by Paul

What effect would having NO vents on any of the radiators be? The house I am in is pre 1900 & boiler is converted from coil to oil. Wife's family had all brand new vents put on every radiator & adjusted. They took them off because the radiators didn't heat well & heated much better without them. Several of the radiators on the 1st floor no longer heat all the way across. I have checked the slope they all slightly slope back toward the inlet valve. I'm at a loss.

On 2016-02-20 16:52:06.156844 by (mod) -

Anon: the number of causes for a single radiator to refuse to heat is limited, but I can't guess what's wrong with yours from just your e-text.

A steam radiator may fail to heat because steam isn't entering it (a blocked steam pipe) or more likely because the radiator is not venting air out to allow steam in, or because of rust or debris clogging at the radiator valve or at the radiator's condensate return (in a two pipe system).

If you have already spent literally hundreds of dollars on this problem that's disappointing since for hundreds of dollars one could have replaced the entire radiator along with its controls. Call your heating company service manager and review the case (politely) with her. Ask for help from a senior technician who can diagnose and fix the trouble.

On 2016-02-20 12:31:26.946190 by Anonymous

My Home is 1865 square foot all the cast iron radiators work except for the upstairs bathroom; I have spent hundreds of dollars to a local repair and fuel oil company with no answers?? What do you suggest? My Brunell steam boiler is 15+ years old

On 2016-02-08 17:15:11.694914 by (mod) -

Search InspectApedia for COLD RADIATORS to see common causes and cures. I suspect that the rads may be improperly sloped, or that a steam inlet or condensate outlet may be clogged.

On 2016-02-08 15:46:14.763465 by Deanna

Hello,
Two of my cast iron radiators in my 1910 home are not functioning properly on the first floor of my house.

I have bought the highest quality Hoffman air valves I could find on the market and changed both of them. The only time the radiators work is when I increase the temperature that thermistat to 85 degrees for 3 or more hours. Please let me know if you have any suggestions.

Question: steam valve replacement: mounting thread problems

July 17, 2011) RJ said:

Can i rethread a radiator in order to properly hold a valve?
or is there any kind of adapter i can insert in a stripped radiator to hold a valve?

Reply:

Great question on radiator repair RJ.
I haven't come across leaks at radiator vents or bleed valves, but it's certainly possible. If the threads are so badly damaged that you cannot seal in a new vent or valve with LeakLok or teflon tape or teflon paste, then it may be possible to drill and re-thread the opening by using an automotive product. We are talking about standard pipe threads.

Provided there is enough thickness in the surrounding metal (cast iron in your case?) you might have to drill out, tap to the next size, and insert a short nipple or plumbing reducer to mount the new vent or bleeder valve.

When I come across a problem like this I tell myself that surely others have run up against it before me, and there is probably already a solution available.

For example auto supply stores carry tools for drilling and tapping out stripped spark plug openings in automotive engines. The stripped opening is drilled to an over-size and an isert is then threaded into the opening to reduce it to the proper spark plug thread dimension.

Ask one of the older guys at your heating supply house for advice too.

Question: water is spitting out our steam vents

(Nov 9, 2011) Dean said:

We recently replaced our our old boiler with a new one. Since the heating season started we have noticed water spitting out of the two air vents on the condensate return line to the boiler after the heat has been on for a while? How can this be prevented?

Reply:

Dean spitting steam vents may need to be cleaned or replaced - I agee that we don't want water spraying into the home.

But watch out: a blockage in the condensate return line could mean abnormal levels of condensate in the system and improper operation. If your steam boiler is using abnormal amounts of water I'd ask for a service call promptly.

Question: combined steam and hot water heat: does the hot water part need an air valve?

(Jan 12, 2012) Saul said:

I have a steam boiler and the house uses steam heat/radiators; however, we added a hot water baseboard system for the basement that works off the steam boiler -- hot water is pumped from the boiler through the pipes to the baseboard heating system; all of the pipes except for the pipes directly attached to the boiler are below the water level of the boiler; does the hot water system need an air bleeder valve?

Reply:

Saul:

Add an air vent on a hot water loop fed by a steam boiler?

Small amounts of air in the hot water heating loop may be pushed around by the circulator pump, return to the steam boiler and vent out with the steam. But larger amounts can block the loop of hot water piping, especially anywhere that it is higher than the boiler and circulator pump themselves.

In my opinion it's good practice to include a manual air bleed valve at the end of the hydronic (hot water) baseboard in any room or building level. It makes bleeding out an air-bound segment of baseboard much easier when that occurs in the future - as it can certainly occur over the life of a system.

Question: loud spitting steam vents

(Dec 30, 2011) Ashley said:

The vents on the radiators in my apartment were incredibly loud, so I had maintenance replace them today. However, one of them is now spitting (a very small amount) of water droplets. It never did that before. The radiator is getting hot, so there's no heating issue. It sounds like spitting vents are a problem and that new vents shouldn't do that! Could the vents be faulty?

(Oct 11, 2012) R said:

If I hammer a nail into my steam vents hole to stop it up, will it explode?... Our steam vent is UNBEARABLE. It is so loud, and rattles, it is next to the bed, and spits water on us. We live in a 5 story building, and we are on the top floor. There are four units below us. Do you see any problem with just corking the love thing up? YES- we could call the super... but 15 phone calls havent fixed it, so we are just taking matters into our own hands.

Reply:

Ashley, very loud spitting steam vents may be damaged or improperly sized for the radiators. They're not costly to replace, but be sure to ask your installer to match the vent to the radiator and system requirements.

R

Don't try hammering anything into a steam vent- when you break it you may be unable to stop steam from pouring into the room. The right repair is to replace defective steam vents that don't close when they should

Question: do steam systems ever create a vacuum?

(June 26, 2012) Is a vacuum created when the fur said:

When the furnace is turned off, the steam condenses. Does this create a vacuum in the system? This could be a problem. How is the vacuum eliminated?

Reply:

If you watch the pressure gauge on a residential steam boiler you will generally see that pressure rises from zero psi cold up to about 0.5 psi hot and then when the system stops heating pressures fall to zero. Residential steamnoperates at low pressure.

But yes, particularly in two pipe steam systems a vacuum can be created in the main piping system when the system shuts off and cools. Air is allowed into the system to accomodate this by vacuum breakers installed on the steam mains.

Question: steam radiators don't get hot. How do I fix this?

(Nov 7, 2012) ashley said:

some of the radiators in my steam system do not get hot what can i do to correct this

Reply:

Ashley, in addition to checking for a stuck shut steam vent, see our STEAM HEAT RADIATOR REPAIR article for diagnostic procedures and repair tips.

Question: how to select the right steam vent

(Mar 19, 2013) John Bolan said:

We recently had a two foot section of steam baseboard installed in our bathroom. It is a small 8x5 foot room. What vent valve should be installed? We are noticing water coming from radiator.

Reply:

John, first get your installer back to fix the leaky condensate return. Then take a look at

• RADIATOR STEAM VENTS, 1-PIPE SYSTEMS


• STEAM VENT TYPES, SELECTION - 2 pipe systems & other steam vents

The steam vent type is first chosen based on the type of steam piping system: one pipe vs. two pipe, as in most installations different vents and controls area used.

Question: how to turn off a radiator

(Oct 27, 2011) Mathew said:
I am trying to prevent my radiator from getting hot. Would turning the steam relief valve off accomplish this? Or would this be dangerous?

Reply:

Matthew: it's better to close the radiator valve.

Question:

(Nov 1, 2011) rory said:
i may have a water logged steam radiator. I'm in an apartment complex, and the steam def works thru out. I have a 3" riser with a radiator on the floor, another T half way up going to a radiator that does work, but they have added a return pipe for condensate.

The problem lies with the radiator on floor level, the piping is tilted, and i just bought a new steam air vent and i tilted the radiator about an 1/2 inch. its a one pipe system and the radiator will not heat up. the second radiator in the line gets really hot. Could the shut off valve be trapping water or does the radiator have that much water that its coming out of the side air vent? and should i continue to drain the water from the union? i'm a novice to this type of steam system. and my land lord stinks and i need heat quickly.

Question:

(Jan 12, 2013) phillip schopper said:
I have discovered a vent valve, typical of that on the end of a radiator, on the heat riser BETWEEN FLOORS. It has begun to leak water badly. Should there even be a valve on a vertical riser? Is this something left over from earlier construction in this old building?

Question:

(Feb 1, 2013) Tracey Bates said:
Our radiators have started leaking from the steam vents and in one of our bedrooms it is leaking from the switch that turns them on and off. How do we fix these problems

Reply:

x

Question:

(Feb 26, 2013) (February 26, 2013) Marc Alexand said:
I have Have one very large Cast Iron Radiator in my bedroom (2nd Floor) which leaks very little water from the valve after a long heating run (about 1 hour). All other radiators run very quietly without a problem except this one. This radiator is the last to heat up.

Why does it take in so much water when it should heat like the others?

Reply:

x

Question: Vent-Rite #11 air valve failure - replacement selection

(Feb 28, 2014) Ken said:
I have a question about a Vent-Rite air valve.
I had a Vent-Rite #11 air valve fail.

I wanted to replace it in kind,but the suppliers around here only carry the Vent-Rite #1
I was wondering if anyone knows what setting on the #1 is equal to the #11.

I called Emerson Swan.

No one was sure.One person said he thought it was full open (8) but I would have thought it would be more in the mid range.
Thanks

Reply:

Ken, you will want to check the Vent-Rite product literature but here's the basic difference between the Vent-Rite #1 and #11:

The Vent-Rite #1 has a 3/32" vent port and operates at 3 psi.

The Vent-Rite #11 has a 1/16" vent port and operates at 6 psi. So I'm not sure that a #11 is a proper substitute for a #1. Both are still produced by the manufacturer. If I were attempting to use the #11 I'm guessing that you'd set it venting down to a reduced level to see how the radiators heat.

You can ask the company for help: Vent-Rite Valve Corporation:
1875 Dewey Ave. Benton Harbor, MI 49022 TEL: (269) 925-8818 FAX: (269) 925-7888

Question: moaning steam vent

(Nov 1, 2014) Anonymous said:
air release valve on riser pipe moans

Reply:

x

Question: which way up for steam vents - vent positoin

Should a steam vent be installed a certain way?

Reply:

Individual steam vent installation instructions may tell you otherwise, and may permit angular or even horizontal installation, but the vents that I see on steam equipment have a definite up-direction necessary for the vent to function properly. SLightly out of vertical may not be a problem but steeper angles or horizontal are likely to mean trouble.

Question:

(Dec 6, 2014) Anonymous said:
One of my home heating radiator is not working properly

Question: leaky steam vents

(Jan 31, 2015) mario carmona said:
put different steam vents on radiator and they all still leak

Reply:

Mario

If the leak is at the steam vent mounting tapping on the radiator then the problem is with inadequate taping or sealing during vent installation.

If the water leaking is from the steam vents themselves then I suspect that as long as you installed the right type and model of steam vents then there is a problem with condensate not returning to the boiler: radiators or piping may be blocked with rust and crud.

Question: steam vent sizes

(Feb 2, 2015) frank said:
steam air valves want to know sizes of four floor building to change steam air vaives.

Reply:

Sure Frank

In More Reading just above you'll find steam vent specs at

STEAM VENT TYPES, SELECTION

Question:

(Feb 3, 2015) Elisa said:
I live in a 1923 building in San Francisco with what appears to be a 2-pipe steam heating system (one pipe at top of radiator coming from the wall with a valve handle, and another near the floor boards with a steam trap/thermostat. The boiler is in an outbuilding about 30 feet away and one floor below the apartments. Pipes travel outside for those 30 feet.

The pipes are slightly pitched upward toward the building, seem to be well insulated, and most are new. The boiler had extensive service in the last 2 years.

However I have been experiencing tremendous noise when the heat is running for the 10 years I've lived here, and no service outfit has offered a solution, other than to suggest tearing up the floor in my unit and replacing all the main pipes.

OK, not going to happen. However in an attempt to figure out a solution myself, I have discovered that a 2-pipe system should not have air vents on the radiators. Two of the four in my apartment do have them. Before I call this out as a flagrant mistake, can you tell me if there is ever a reason a 2-pipe steam system might have them legitimately?

Could our system be some strange hybrid of 1 and 2 pipe system for example? When the building was constructed the boiler was directly beneath the apartments, but that space was later converted for commercial use and the boiler was moved to this outbuilding at a distance.

Maybe in that conversion they did something wrong? I'm willing to invest time and some money to alleviate the noise issue (rattling, gurgling, sloshing, hammering, clunking, you name it in all radiators and underneath the floorboards), but need some understanding of what might have been done earlier that was not correct.

Reply:

Elisa that question is a bit more than I can make-out. But in general, water noise in steam systems means there's a condensate return or condensate handling problem. I figure an on-site steam heating tech ought to be able to help sort this one out.

...

Continue reading at STEAM VENTS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• STEAM HEAT RADIATOR REPAIR
• RADIATOR VALVES & HEAT CONTROLS
• STEAM VENTS - home
  • STEAM VENTS, 1-PIPE SYSTEMS
  • STEAM VENT TYPES, SELECTION
  • STEAM VENTS, 2-PIPE SYSTEMS
  • STEAM RADIATOR VENT CLEAN & TEST
  • STEAM RADIATOR VENT REPAIR
  • STEAM VENT TABLE, CROSS REFERENCE & SOURCES

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STEAM VENT FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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