Steam heating boiler pressure & pressure level troubleshooting questions & answers.

This article series describes the normal operating pressure range for residential steam heating systems and for commercial or high-rise building steam heating systems.

This article series provides an illustrated inspection and repair guide to Steam Heating Systems. The page top photo shows a modern steam heating boiler.

Steam Heating Boilers Operating Pressure Q&A

These questions and answers about the setting and maintenance of proper residential steam boiler pressure were posted originally at STEAM BOILER PRESSURE - topic home, - be sure to read our diagnosis and repair advice found there.

Can we increase the steam boiler pressure up fdrom 1 psi to 2 psi to get heat into cool radiators?

In a 7 story, 88 unit midrise with Eastmond single pipe steam heating system (4M BTU @ 125 hp).

Some steam supply pipes were retrofitted after failing decades ago.

Running smoothly at 1 PSI.

Only on extremely cold days does the system run adequately to provide heat to the most distant unit (D aperture in vent).

During periods of moderate OD temperature the unit remain cool when others may overheat.

What effect will increasing the boiler pressure to 2 PSI have? Will we have to re-vent the entire building (250+ convectors) with 4s and 5s except for the most distant units Ds? Any other ideas? On 2023-02-21 by Joey

by InspectApedia Editor - Better to look for a steam vent that's clogged or failing if you have intermittent or too little heat

@Joey,

I can't advise increasing the steam boiler pressure as you suggest, though the exact effect can't be predicted by a brief text.

Increasing steam pressure is a too-common "band aid" repair done by a technician who doesn't know steam system operation.

Consider that if the heating system worked properly at original installation, then it was designed to work at normal low steam pressures such as in the 1 psi range.

If you're now having heat delivery problems, the most obvious first place to start is with the steam vents at your 250+ convectors. A vent that's clogged or failing means intermittent or too little heat.

So try replacing some of those vents, starting with the coldest convectors - most distant.

Other more costly trouble could be rust and scale clogging convector piping, but do the vents first.

Steam boiler is set to 95 psi, we think we can lower that; what do you think?

I work in an institution that has a steam boiler it provides steam for hhw, in addition to the central kitchen and laundry.

Our setpoint is 95 psi, but we determine from the steam saturation table that we can lower the setpoint substantially. I would like to hear an opinion on this subject.

Thank You Keith - On 2023-02-14 by Kevin Keith Smith

Reply by InspectApedia Editor

@Kevin Keith Smith,

I have no information at all about your institution's size, location, usage levels, etc.

Take a look at the section titled:

Relationship of Boiler Pressure to Water Temperature in Steam Boilers

And its accompanying table on this page

STEAM HEATING SYSTEM OPERATING TEMPERATURE

Where we mention a commercial boiler system operating perhaps between 20-40 psi.

Please also be sure to read about BLEVE explosions and the risk and danger involved at

BLEVE: BOILING LIQUID EXPANDING VAPOR EXPLOSION

Note by InspectApedia Publisher - About commercial high-pressure steam system hazards

@Kevin Keith Smith,

Note of Details for other readers:

1. An important distinction is that this reader's is a commercial high-pressure steam system -

not the subject of the steam boiler pressure on this page where we focus on low pressure residential steam heating systems.

The hazards that come from making a mistake in setting high pressure steam pressure are enormously greater in part because of not just higher operating pressure but higher temperatures.

A description of a high pressure steam system that can give insight into its extra controls and complexity compared with residential steam is at

STEAM BOILERS GENERATORS CONTROLS, PRATT

In contrast, residential "low pressure" steam systems like those described above on this page operate usually under 1 psi.

Some useful definitions and properties of steam:

"Saturated steam" or "dry steam" can be defined as steam in which all of the water molecules are in a gaseous state. Actually even high temperature/pressure saturated steam systems are not likely to operate at a perfectly-saturated 100% level. Dry steam is what's wanted for use in heating systems.

The temperature of steam will be about the same as the boiling point of water at that pressure, where the boiling point of water at 1 Atmosphere (sea level or about 14.8 psi) is 212F or 100C.

Increasing the pressure in a steam system by 1 psi raises the boiling point of water and the steam temperature by about 3 degF.

The boiling point of water and thus the approximate steam temperature at 95 psi is about 324 degF or 162 degC!

Un-saturated steam or "wet steam" contains some water (droplets) mixed in with the steam - such as what comes out of a boiling tea kettle. Wet steam, in a heating system, can be corrosive and might also be less efficient at heat transfer from steam to the radiating device.

Superheated steam is steam that's at a temperature above the boiling point of water at that pressure.

2. The reader is probably correct that his system's operating pressure could be adjusted,

but we don't know enough nor have enough information to speculate on a specific change, particularly where there are significant safety risks. This is a question for an on-site, high-pressure commercial steam technician or engineer.

The U.S. Department of Energy offers an online steam modeling tool for high pressure steam systems that "Calculates saturated liquid and gas properties for a given pressure or temperature using the IAPWS Industrial Formulation 1997." found at www4.eere.energy.gov/manufacturing/tech_deployment/amo_steam_tool/propSaturated

but

Watch out: readers should beware of modifying their steam system away from its original design without consulting an on-site expert. There are simply too many local variables in steam system requirements, operation, distribution, etc. for a "one-size-fits-all" off the cuff answer.

Besides inviting readers to scan through our steam heat articles and ask questions, here is a copy the contents of an easy-to-understand steam heat course offered by India's Bureau of Energy,

STEAM SYSTEM COURSE [PDF] Bureau of Energy, Government of India, 4th Floor, Sewa Bhawan, R. K. Puram, New Delhi - 110066 (INDIA) Tel: 011-26766700, retrieved 2023/03/03, original source: beeindia.gov.in/sites/default/files/2Ch3.pdf

Steam system is short cyclilng and air spits out of radiator vents

I’m very new to the world of steam heating and have just come across a system that baffles me.

Old three story home that was converted into a business. Used one boiler to heat all three floors and two basement radiators.

Three above ground floors all have single pipe radiators but both basement radiators are the two pipe type.

They also seem to not have steam traps on them and one of them looked like it had an air vent on it.

System seemed to be working fine until a recent boiler replacement.

Now, the system still heats for the most part but short cycles and the basement radiator with the air vent is spitting out a good amount of water from it. Thoughts? - On 2022-02-14 by Disan Munoz

Reply by Inspectapedia Com Moderator

@Disan Munoz,

Flying blind since I can't see your building, my GUESS is that those basement radiators are heating by hot water not steam.

It is common in buildings to heat radiators on the same floor as the steam boiler by circulating hot water out of the same boiler through those rads - and more-effective since you'd have a devil of a time pushing steam "down" into that heating loop.

 

Should my residential steam boiler be cycling on and off on pressure while thermostat is not satisfied?

Should my residential steam boiler be cycling on and off on pressure while thermostat is not satisfied?

Pressure control set at approximately 2 psi with a reset of 1 psi. My plumber originally told me that the boiler should not be cycling on pressure but now tells me that is normal. On 2021-03-03 by Chuck Lambert

by inspectapedia.com.moderator

@Chuck Lambert,

The answer depends on the on-off cycling rate.

If your boiler is cycling on and off rapidly, every minute or so, then something's wrong, perhaps with condensate return flow or with a control switch itself

Steam boiler won't come on unless we set the Pressuretrol to 5 psi!

My boiler won't fire unless the pressuretrol is cranked up to 5psi. I don't want it to run that high, I want it to run between 0.5 and 1.5. Any ideas what is going on here? - On 2020-09-30 by Tyler

Warning by (mod) -

Tyler

Usually when someone is setting a residential steam boiler to abnormally high pressure it's because their system is not delivering steam to one or more of the radiators;
In turn, that's often because there is a piping or distribution problem such as clogged supply pipes, clogged condensate return, malfunctioning steam vents.

I agree that it's not a good solution to just push up the pressure. Ask your service tech to investigate and tell you (and me) what problem she or he finds.

"Medium" Residential boiler shows only about 0.5 psi on a 30 psi pressure gauge - what pressure gauge do I need?

I have a medium residential steam boiler with a new 30PSI gauge on it. The gauge does not move at all. It was mentioned that the whole system only heats at about 0.5 PSI. The boiler's PRV is rated at 15 PSI. Do I need a 30PSI gauge, or can I downsize to a 15PSI so that the boiler's pressure gauge actually does something? On 2020-09-20 by Reid

Answer by (mod)

Reid

That gauge is the wrong one and won't be useful.

You could replace it with a steam boiler low pressure range gage but take care not to create a bigger problem if the mount area is corroded

What should the temperature drop to in an industrial steam boiler that is shut down?

When an industrial boiler is shut down, with the heating source off, would it you expect the residual temperature of the boiler to not drop below 100C within the first 24 hours it was down? On 2020-02-24 by RAS

by (mod) -

RAS

Yes - 100C or 212F (boiling) is pretty hot. B

ut, then, we have no information about the size, thermal mass, residual heat in the whole heating system nor its initial operating temperature, insulation, etc.

is this a quiz question?

by RAS

Thank you very much for your quick reply. You do, indeed respond promptly, as advertised above.

No, it was not a quiz question at all, and I realized before asking that there are too many variables and I provided way too little information to make any kind of definitive statement, nor did I expect one.

I am working with a facility on a project not directly related to utilities or steam. For whatever reason, it would be helpful to what I am doing if they would shut down their boiler for 24 hours, but I didn't want to ask something of them that they would not want to do, which would be the case if they were to lose temperature in the boiler.

As long as its possible, I won't feel out of place or uncomfortable suggesting it.

Having visited this site for information in the past, I want to thank you once again and let you know that there are those of us out here who greatly benefit from and appreciate knowledge and expertise found here. You are a tremendous resource!

Thank you very much for your quick reply. You do, indeed respond promptly, as advertised above.

No, it was not a quiz question at all, and I realized before asking that there are too many variables and I provided way too little information to make any kind of definitive statement, nor did I expect one.

I am working with a facility on a project not directly related to utilities or steam. For whatever reason, it would be helpful to what I am doing if they would shut down their boiler for 24 hours, but I didn't want to ask something of them that they would not want to do, which would be the case if they were to lose temperature in the boiler. As long as its possible, I won't feel out of place or uncomfortable suggesting it.

Having visited this site for information in the past, I want to thank you once again and let you know that there are those of us out here who greatly benefit from and appreciate knowledge and expertise found here. You are a tremendous resource!

Reply by (mod)

Thank you so much for the follow-up, RAS.

We have worked hard on this information and website for many years, seeking to provide researched, unbiased information, so I'm of course grateful when a reader finds it useful. No one knows it all, so working together helps us both.

I'd need to know more about the application, but in general, shutting down a boiler does not itself harm any equipment, but depending on what the boiler is doing, the temporary loss of heat can of course be a problem. A residential steam heat system won't ever be much above boiling (100C) as those operate at very low pressure.

Commercial and high pressure steam systems can run at much higher temperatures and of course have different controls and different safety concerns.

Whether or not your particular system can shut down the boiler for 24 hours probably depends on the application of the boiler and whom its shut-down affects as well as whether or not there is a backup or alternative system to keep critical functions working.

Can you use a Watts 1156 feeder on a steam boiler?

Water is coming out of the vents or air bleeders on our steam radiators.

Will watts 1156 prevent that

Can you use a Watts 1156 feeder on steam boiler On 2019-09-10 by Duane -

Answer by (mod) - Watts 1156 pressure regulator on cold water supply ?

Sounds wrong.

Duane

If you have a steam heating system and water is coming out of the steam vents then your system is flooded and your automatic water feeder is NOT WORKING. You need to call for repair.

A Watts 1156 Pressure Regulator is normally used on hot water (hydronic) heating boilers; you could install such a pressure regulator on the cold water supply line serving a steam boiler but NOT as a repair for the problem you describe and NOT as an automatic make-up water feed valve.

This valve is a pressure reducer and is not intended for regular addition of make-up water that is required by a steam boiler.

See the Watts 1156 instructions at

WATTS PRESSURE REGULATOR 1156 MANUAL [PDF] retrieved 2019/09/09 original source: media.wattswater.com/1910265.pdf

In the ARTICLE INDEX you will find articles describing the necessary controls for steam boilers including

a LOW WATER CUTOFF and an AUTOMATIC WATER FEEDER for steam boilers: those are the proper controls for a residential steam heating system.

Should the Hartford Loop be higher than the condensate return line on my steam boiler?

Should the top of the Hartford loop be higher than the condensate line on a gravity return system? On 2018-12-02 by Tim Kline

by (mod) - Yes

Yes at the boiler.

In the ARTICLE INDEX given at the end of this article please see details and illustrations at
the

HARTFORD LOOP 

Article listed there.

Steam boiler is at 28 psi and water is coming out of my return on my American Standard boiler

II have a pressure of 28 psi and water is coming out of my return how can i lower the water pressure from my steam American standard boiler - Ronald 1/13/2013

Reply: 28 psi on residential steam heat is very unusual, probably unsafe - shut the system off

Ronald,

Watch out: If your heater is a residential steam heating system it is operating at an abnormally high temperature and is unsafe. Turn the system off immediately and call your heating service company.

If your heater were a residential hot water heating boiler (hydronic heat) its pressure might be close to the upper end of normal operating pressure - and the leak at the valve could be due to a valve problem or to any of quite a few other causes.

See RELIEF VALVE LEAKS for procedures to diagnose and fix leaky TP relief valves. See the links just below for information on how the steam heating system pressure is controlled and set.

 

Question: Service tech just set our residential steam boiler pressure to over 30 psi!

The HomeServ tech just left after installing a new auto water feeder, and the PSI gauge on my steam heater is off the chart, over 30 PSI.

I shut it down and called HomeServ and they said leave it on and they'll come in the morning.

How do I lower the PSI myself so I can leave it on tonight and my little kids (two with strep) don't freeze? Thanks! 2/22/2012

Reply:

Watch out: If the PSI gauge is showing abnormal pressure and the gauge itself is working properly the system is unsafe and should be shut down.

Call someone else and fire that technician who, from your description, doesn't know the difference between a hydronic (hot water) boiler and a steam boiler; and from your description the system sounds unsafe

 

Comment: too-high steam pressure traced to a blocked sensor on steam pressure control

Pressure on gas steam boiler was rising far too high, so high that the pressure relief valve released twice when it hit 15 psi (as it was supposed to do).

Good buddy who really knows his stuff checked everything from pressure valve to pressuretrol. Nothing . He then checked "pigtail" and found blockage .Problem solved!! - Ken 11/24/12

Reply:

Thanks for this note it may help other readers

 

What is the proper setting for a Honeywell PA-404-A 1099 Presstrol on a steam boiler

Does anyone know the proper setting for a honeywell pa-404-a 1009 prestrol control for a weil-mclane steam boiler - rick 9/11/11

Reply:

Rick the exact pressure needed varies by installation but in a low pressure residential steam system the pressure range is usually between 0.2 and 0.4 psi.

See details at STEAM BOILER PRESSURE

...

What are the right pressuretrol settings for second floor in an office buildings

I just installed a 299 MBH gas fired steam boiler and connected to an existing system serving the second floor of an office building, approx floor area is 2,600 sq ft.
Existing EDR calculated as approx 900 sq. ft. The boiler started up successfully yesterday and I have been testing it ever since.

Everything seems to be working fine. My question is what would be the right pressuretrol settings: I am using 1 psi cut-in and 1 psi differential and everything seems all right, but I may be missing something, maybe the boiler could work more efficiently with a lower or higher cut in pressure. (Oct 16, 2014) Antonio said:

I have a gas-fired steam boiler that has worked flawlessly since its installation six years ago. Suddenly it is overfilling.

I let out several extra gallons a day to reduce the level in the sight glass. Shoudl I replace the automatic feed? It is attached to the hot water heater, unlike previous installation I have had in othe rhouses where it is connected to the cold water line.

I sit possible that excess pressure from the expansion in the hot water supply line is forcing water past the automatioc feed? What could cuase this condition? (Dec 15, 2014) Kevin M

Reply:

Kevin

Over-filling of a heating boiler is indeed usually a problem with the automatic water feeder, more rarely leaks into the boiler from a tankless coil.

 

What does internal siphon gauge in a steam boiler do?

What does internal syphon gauge do? On 2018-01-03 by Jay

by (mod) - purpose of the steam boiler syphon gauge (siphon gauge) (snubber)

Jay

A steam boiler siphon gauge (some sources spell it syphon gauge) or snubber attempts to stabilise the boiler pressure gauge and thus the accuracy of its readout by a small piping loop that reduces the effect on the gauge of boiler surging or pulsation.

Particularly because residential steam boiler operate at very low pressure, under 1 psi, the siphon helps stabilize the gauge that hs to operate in a low pressure range.

I attach a steam boiler siphon gauge siphon tube photo from Glival.

 

The pressure gauge on my boiler is way over 30 psi - how can I fix it so we have heat?

The HomeServ tech just left after installing a new auto water feeder, and the PSI gauge on my steam heater is off the chart, over 30 PSI.

I shut it down and called HomeServ and they said leave it on and they'll come in the morning. How do I lower the PSI myself so I can leave it on tonight and my little kids (two with strep) don't freeze? Thanks! 2/22/2012

Reply:

Watch out: If the PSI gauge is showing abnormal pressure and the gauge itself is working properly the system is unsafe and should be shut down.

But before going to extreme measures,

1. Is yours a steam boiler or a hot water heating boiler? If it's steam, I would be stunned if the pressure gauge scale read anywhere neaer 30 psi - as steam residential steam boilers run in the 0.2 - 0.5 psi range - that is, under 1/2 psi.

So first, what kind of boiler have we got?

2. Even if your boiler is a hot water (not steam) boiler, if the pressure is over 30 psi the system would be unsafe, risking a BLEVE EXPLOSION so it would have to be left OFF.

So Try this: tap gently on the pressure gauge: if the gauge needle drops, then the gauge was simply stuck and you may now see a lower and safe boiler pressure.

Watch out: And if yours is a hot water boiler (not steam) also take a look at the pressure relief valve: if it's leaking the boiler is unsafe and must be left OFF.

See examples at RELIEF VALVE LEAKS

Call someone else and fire that tech - from your description the system sounds unsafe

 

Thank you to our readers for their generous comments

by RAS

Thank you very much for your quick reply. You do, indeed respond promptly, as advertised above.

Having visited this site for information in the past, I want to thank you once again and let you know that there are those of us out here who greatly benefit from and appreciate knowledge and expertise found here. You are a tremendous resource!

LeFoo Steam Boiler Pressure Control Co Comments on Inspectapedia article

LEFOO
Thank you very much for seeing this article broaden my horizons.

As a staff member of a pressure switch manufacturer, I usually focus on products and rarely understand downstream applications.

This time I learned about the common sense information of boiler machines, and I am very grateful to everyone for your feedback on the market. We will further improve the quality of our products. On 2021-08-16

Moderator reply:

Thank you for the kind words, LeFoo Company (un-named writer). We include your product image above- a steam boiler pressure control produced by Lefoo, website lefoo [dot] com

To protect our readers from possible malware Comment Box does not permit posting of links nor does our policy permit posting of advertisements.

However we very much welcome technical content suggestions, questions, criticism, and in those cases we are quite able and pleased to cite and provide contact information (including website links) to content contributors. We can also be reached by the CONTACT link found at the top or bottom of any InspectApedia.com page.

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

Or see PRESSURE & TEMPERATURE SETTING, CONTROL FAQs - questions & answers about pressure on hot water - hydronic - heating systems (not steam heat)

Or see these

Recommended Articles

• GAUGES, HYDRONIC BOILER - different pressure readings on hot water heating boilers
• PRESSURE CONTROL, STEAM BOILERS
• RELIEF VALVE, TP VALVE, STEAM BOILER
• STEAM BOILER PRESSURE - topic home,
• STEAM BOILER TEMPERATURE
• STEAM HEAT RADIATOR REPAIR
• STEAM HEATING SYSTEMS & CONTROLS - home
• STEAM PRESSURE GAUGE
• WATER FEEDER VALVE, STEAM

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INDEX to RELATED ARTICLES: ARTICLE INDEX to STEAM BOILERS

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