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Steam heating boiler pressures:
This article describes the normal operating pressure range for residential steam heating systems and for commercial or high-rise building steam heating systems. We include citations of steam boiler explosions and describe probable differences in boiler explosion causes between early steam heat history and modern steam boiler use. The article also provides links to details about the pressure control and safety controls on steam heating systems & boilers.
This article series provides an illustrated inspection and repair guide to Steam Heating Systems. The page top photo shows a modern steam heating boiler.
Residential steam heating systems are almost always designed to operate at very low pressures, typically around 0.2 psi to a maximum of 0.5 psi - that' s 1/2 of one psi. Click to enlarge and you can see the actual pressure settings on the steam boiler control shown at left.
0.2 psi = 0.014 Bar or about 1378 Pascal of pressure - typical low-end of residential steam boiler pressure settings.
0.5 psi = 0.034 Bar or about 3447 Pascal of pressure - typical high-end of residential steam boiler pressure settings
Watch out: If your residential steam boiler is operating at higher pressures that may be an indication that a service technician or owner was having trouble getting heat distributed through the building. Rather than finding and fixing the problem, someone is trying to "force" the steam around the system.
[Click to enlarge any image]
High rise buildings and larger facilities using steam for heating may employ a high-pressure steam heating system. According to a University of Idaho engineering text we cite below, a 30 psi high pressure steam system might provide sufficient pressure to deliver steam heat to a building 40 stories in height. So we might see 15 psi for a 20 story building steam system.
20 psi = 1.4 Bar or about 137900 Pascal of pressure - typical low-end of high-rise building steam boiler pressure settings.
40 psi = 2.8 Bar or about 275790 Pascal of pressure - typical high-end of high-rise building steam boiler pressure settings
Why Might Steam Pressure Be Set Too High?
An experienced steam heat service technician will look at the operating pressure of your steam heating boiler and if it is not set to a normal level, the technician will look for the reason. Examples of problems that can affect the flow of steam heat through the system, leading to attempts to over pressurized the system include
Blocked condensate returns at individual steam radiators
Improperly relocated steam piping that has the incorrect slope
Radiator valves that are not operating,
Radiator steam vents that are not operating properly
see STEAM VENTS
Steam traps clogged by rust, blocking condensate from leaving the radiator
see STEAM TRAPS
For details about radiator problems see RADIATORS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Watch out: do not modify a steam boiler pressure control switch to try to force steam heat to cold radiators or to higher floors. Doing so makes the system less efficient, fails to find and correct the underlying problem, and in some situations it could make the heating system unsafe.
Steam Boiler Pressure Control Safety Switch Operation
The pressure control switch on a steam heating boiler is designed to shut the heating system down should unsafe high pressures develop.
As we emphasize at our description of pressure gauges on a steam boiler, residential steam heating systems are almost always designed to operate at very low pressures, perhaps around .5 psi - that' s 1/2 of one psi. You should see similar settings on the pressure gauge and on the steam pressure control switch (the gray box our photos of steam pressure switches shown here) on your boiler.
Because the operating temperature, pressure, and form of heat distribution are different from hot water heat (typically 20-30 psi of hot water), steam boilers (typically less than 0.5 psi steam) use use controls that monitor steam pressure operated controls like the Honeywell steam pressure control shown below.
Reader Question: the gray box on my steam boiler is set under 2 psi but the boiler pressure is 7-8 psi. Is this normal and safe?
The gray box on my steam boiler is set low (less than 2psi) but the glass pressure gauge is reading 7 or8 at times. Is this normal /safe? - Brian 11/21/12
One wouldn't expect a boiler to blow up at 14 psi, but I agree that the system is not set nor operating at safe normal pressures. I suggest calling a service tech promptly.
Usually residential systems operate at lower pressures, less than 1 psi, often around 0.2 to 0.4 psi.
Since your steam boiler pressure control valve is set under 2 psi and the boiler pressure is way over that, and assuming that your steam boiler gauge is working and not "stuck" at an abnormal reading , the problem may be the pressure control valve itself.
Reader follow-up: changing out the steam pressure control valve did the trick
got the tech. he took off the gray box on my newly installed williamson boiler (2 weeks ago) and replaced it with the one from my older rotted out 12 year old Burnham! both gray boxes are honeywell and seem to be identical. works ok now. go figure!
Steam Boiler Pressure Gauge and Normal Pressure Ranges
Pressure and Temperature gauge on steam heating boilers: Residential steam heating systems are almost always designed to operate at very low pressures, perhaps around .5 psi - that' s 1/2 of one psi.
You should see similar settings on the pressure gauge (at left in our photograph) and on the steam pressure control switch (the gray box at right in our photo) on your boiler.
If your heating system uses forced or gravity circulated hot water rather than steam, controls and gauges are different:
see GAUGES on HOT WATER BOILERS
or see PRESSURE GAUGE, BOILER for more details about pressure gauges on hydronic (hot water) heating boilers. These are not steam systems.
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
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.
Reader 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
Thanks for this note it may help other readers
Reader Question: 28 psi and water 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
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.
Steam Boiler Accidents & Explosions
Steam boiler explosions early in the history of steam boilers were often related to leaks, loss of water in the boiler, absence of safety controls like the HARTFORD LOOP and LOW WATER CUTOFF VALVE. In modern steam boiler explosions we are of the opinion that other forces might be at work, such as improper maintenance, tampering or work performed by inadequately-trained personnel.
Two steam boiler explosions occurring in September 1867 were reported in the New York Times on 15 September 1867. Paraphrasing and excerpting the original news article from the Times archives: "At Springfield IL a boiler 24 feet long and 3 1/2 feet in diameter, was blown to pieces as if it had been paper; the flour mill in which it was situated was almost entirely destroyed. ... All the information that the public are likely to get regarding the cause of the explosion is the reporter's statement that the engineer was not in the room when the "accident" occurred, and that the iron of the boiler was probably defective ... "
Schweber, Nate and William Neuman, "They Moved to Find a Better Life. It Got Worse", The New York Times, 21 December 2016. Excerpting:
"... on Dec. 7. It was a “freak accident,” according to Mayor Bill de Blasio: A valve had come off a radiator in the room where the girls slept, filling the room with intense heat and steam. It was not clear how long the steam had been pouring out, or whether the girls’ cries had gone undetected. A neighbor, hearing the parents’ screams, called 911 at 12:08 p.m. Fifteen minutes later, the girls were declared dead.
Mr. Ambrose said that he and his wife were awakened at about 6 a.m. when a valve popped off the radiator in the living room, where they slept. They replaced it, he said, but did not check on the girls. Ms. McGuire later went out to run errands, her husband said, and he fell back asleep — apparently never realizing that the radiator in the adjoining room where the girls slept had also malfunctioned. At about 11:45 a.m. Ms. McGuire returned to the apartment and soon went into the girls’ room to find them turning purple and blistering from the intense heat and scalding steam.
Police and city officials are investigating the episode but have yet to provide a detailed explanation of what occurred, other than to say that a valve came off the radiator in the girls’ room, allowing steam to escape."
References for Steam Heating System Pressures & Temperatures
Holohan, Dan, "A Steam Heating Primer", HeatingHelp.com, (2014), retrieved 2016/12/21, original source: https://heatinghelp.com/systems-help-center/a-steam-heating-primer/
"BUILDING HEATING SYSTEM DESIGN" [PDF], University of Idaho, lectures on thermodynamics, retrieved 2016/12/21, original source: http://www.webpages.uidaho.edu/mindworks/Thermodynamics/Lectures/L14/Buildling%20Heating%20System.pdf
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Weil McLain Model 78 Boiler Manual, Boiler for gas, light oil, Gas/Light Oil fired BUrners, Installation, Start-up, Parts, Maintenance instructions, Part No. 550-141-705/0600, Weil-McLain Administrative Office, 999 McClintock Drive, Suite 200, Burr Ridge, IL 60527
Tel: 855-248-1777 Consumer Inquiries: 800-368-2492 Technical Services: 800-526-6636 Technical Support for Contractors Only.
If you are a homeowner and are experiencing a problem with your Weil-McLain equipment, the first step you must take is to contact your installer or locate an HVAC contractor in your area. Website: http://www.weil-mclain.com
The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update, (see next item in this list). ITT Fluid Technology,
1133 Westchester Avenue
White Plains, NY 10604,
tel +1 914 304 1700 fax +1 914 696 2950 www.ittfluidbusiness.com
Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
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