LARGER VIEW of a heating boiler pressure temperature gauge Steam Heating System Operating Temperature

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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.

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Residential Steam Boiler Normal Temperature Ranges

Steam pressure gauge on a steam boiler

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.

The steam boiler pressure is controlled by the PRESSURE CONTROL, STEAM BOILERS - the gray box shown in our photo.

The controls in this photo are discussed in more detail

[Click to enlarge any image]

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 0.31 psi 0.5 -1.1 psi 1.2 - 1.31 psi 3.31 psi 5.31 psi 9.31 psi 15.1 - 15.31 psi 25.31 psi 31.31 psi 41.31 psi
Water Boiling Point 212 °F 213 °F 214.5 °F 216 °F 222 °F 228 °F 238 °F 250 °F 267 °F 276 °F 288 °F
Steam Boiler PSI 50.3 psi 60.7 psi 75 psi 100.2 psi 123.5 psi 142.3 psi 181.1 psi 232.6 psi 262 psi 275 psi 294 psi
Water Boiling Point 298 °F 308 °F 320 °F 338 °F 352 °F 362 °F 380 °F 400 °F 410 °F 414 °F 420 °F


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.

1.Other assumptions:

  • 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:
  • JGB Enterprises, "Steam Temperature - Pressure Conversion Guide", JGB Enterprises, Inc., 115 Metropolitan Drive, Liverpool, NY 13088 (Syracuse Area) (315) 451-2770 retrieved 2016/12/21, original source: literature/steam-temperature-pressure-conversion-guide.asp
  • TLV, "Calculator: Saturated Steam Table by Pressure", used 2016/12/21, original source:

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 :

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.

Details are at STEAM BOILER PRESSURE - home.

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.

Also take a look at the dial setting on your PRESSURE CONTROL, STEAM BOILERS

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.



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