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Steam heating boiler operating temperatures:
You won't normally see a temperature gauge on a steam boiler: the boiler has to "boil" water to make steam so it's a safe bet that water in the boiler, when it's making steam, will be around the boiling point. Here we explain where and how and to what numbers the temperature is controlled on residential steam boilers. We include a table illustrating the increase in water and steam temperatures produced in a steam boiler that operates at both low pressure and also at higher pressures.
This article series answers most questions about all types of steam heating system controls, operations, troubleshooting, and repair.
Residential Steam Boiler Normal Temperature Ranges
Temperature gauge on steam heating boilers:
Because a steam boiler makes heat by producing steam - by boiling water, at sea level, the temperature at the boiler will be boiling or 212 °F or close to that figure.
The actual steam boiler temperature may be a bit lower at high elevations above sea level, and the steam boiler temperature will be a bit higher than 212 °F for boilers operating at slightly higher pressures, as we'll illustrate in a table below.
Relationship of Boiler Pressure to Water Temperature in Steam Boilers
The temperature of heated water can exceed 212 °F when water is heated under pressure - producing superheated water than can flash to steam. See BLEVE EXPLOSIONS for details. However a residential steam boiler pressure is so modest (0.2 psi to 0.5 psi) that the temperature increase above 212 °F will be no more than about 220 °F.
A commercial boiler system heating a high-rise building may be operating at much higher pressures, perhaps 20 to 40 psi in order to be able to force steam to 20 or 40 floors of building height. For each psi increase in pressure in the system, the boiling point of water (assuming no coolant or antifreeze mixture has been added) will be increased by about 3 °F.
Increase in Water's Boiling Point as Boiler Gauge Pressure Increases1
Steam Boiler PSI
0 psi = 1 ATM
0.5 -1.1 psi
1.2 - 1.31 psi
15.1 - 15.31 psi
Water Boiling Point
Steam Boiler PSI
Water Boiling Point
Boiler PSI in the table above is gauge pressure. That means that 0 psi on the gauge or in the boiler is actually at 1 ATM at sea level, or 14.69 psi true pressure.
Using the Engineering Toolbox for water boiling point changes as pressure increases is a bit awkward as the toolbox centers its data around 1 ATM or 14.69 psi having a boiling point of 212 °F. To relate the engineers' toolbox to the "real world", reading 1 psi on the boiler gauge would be 1+14.69 psi or 15.69 psi - numbers that do not map to the engineers' table. So our data in the table above is approximate to the real world.
No chemical additives are mixed in to the water. Adding an antifreeze or coolant mix will increase the boiling point of water.
The boiler is at sea level or 1 ATM of pressure (14.69 psi ambient pressure at sea level). The boiling point of water will be lower at higher elevations. At one mile above sea level the boiling point of water drops from 212°F. to 203°F.
2. Original sources for steam pressures and temperatures: :
Engineering Toolbox, Water Pressure and Boiling Points, retrieved 2016/12/21, original source: http://www.engineeringtoolbox.com/boiling-point-water-d_926.html
JGB Enterprises, "Steam Temperature - Pressure Conversion Guide", JGB Enterprises, Inc., 115 Metropolitan Drive, Liverpool, NY 13088 (Syracuse Area)
firstname.lastname@example.org retrieved 2016/12/21, original source: http://www.jgbhose.com/technical-reference- literature/steam-temperature-pressure-conversion-guide.asp
TLV, "Calculator: Saturated Steam Table by Pressure", used 2016/12/21, original source: http://www.tlv.com/global/TI/calculator/steam-table-pressure.html
Portions of the data above was excerpted from the DuraTherm article below, with the caveat that within that article the author's calculations of water temperature are inconsistent and may not represent exact field conditions.
"The Effects of Pressure on Boiling Point Temperatures", [PDF] DuraTherm Heat Transfer Fluids, retrieved 2016/12/21, original source :https://durathermfluids.com/pdf/techpapers/pressure-boiling-point.pdf
Residential steam heating systems are almost always designed to operate at very low pressures, perhaps around 0.2 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.
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.
Controlling Room Temperature with Steam Heating Systems
This article discusses the acutal water temperature in a steam heating system.
To control room temperature you will want to control the steam radiator itself. Both the control or shut-off valve at the steam radiator and also its steam vent will affect the radiator's output or the heat that it sends into the occupied space.
Questions & answers or comments about heating system operating pressures, temperatures, and controls for hot water and hot air heating systems and for warm air furnace systems
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 "[Heating] System Pressure in Typical Hydronic Systems", TechTalk, Vol. 20, Issue 1, January 2005, ITT Industries, Fluid Handling [copy on file]
 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
 "Warm Air 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
 Installation Guide for Residential Hydronic Heating Systems
 Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
 The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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