Guide to Heating System Pressure & Temperature Gauges
GAUGES ON HEATING EQUIPMENT - CONTENTS: Heating System Gauges: Pressure and Temperature Gauges on Heating Boilers - Troubleshooting & Repair Guide. What are the normal hot and cold operating pressures of hydronic heating boilers? What are the normal hot and cold pressures of residential steam boilers? Where & how do I set the boiler pressure and temperature controls? Where & how do I set a steam boiler pressure and temperature? Where & how do I set the furnace temperature control? Troubleshooting heating system boiler controls and switches
POST a QUESTION or READ FAQs about heating boiler gauges; how to read heating system pressure and temperature, what are the normal system pressure and temperature? boiler gauge leaks, replacement, repair.
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Heating boiler pressure & temperature gauges: Here we provide an inspection and repair guide to Heating System Gauges: Pressure and Temperature Gauges on Heating Boilers. We also describe the normal operating pressures for hot water hydronic heating boilers and for residential steam boilers.
You will also see that
this article series answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.
Hydronic (hot water) Heater Pressure Gauge and Normal Pressure Ranges
Pressure and Temperature gauge on hot water or hydronic heating boilers: this gauge displays the heating boiler internal pressure and temperature.
[Click to enlarge any image]
Hydronic boiler pressure: Typical pressure for a residential boiler serving a two story home would show 12 psi cold, and less than 30 psi hot.
Over 30 psi boiler pressure will cause the pressure relief valve to open.
Hydronic boiler temperatures: When there is no call for heat and if the boiler does not make hot water for a tankless coil, the boiler temperature will fall to room ambient temperature.
Typical operating temperature
settings on a boiler call for a Low temperature (boiler cut-in) between 120 and 160 °F.
Typical operating temperatures on a hydronic boiler call for a high temperature (boiler cuts off) of 180-200 °F.
Over 200 degrees F. we're at risk of spilling at the pressure temperature relief valve.
Typical operating temperature observed at the gauge will be below the high, and can be as low as
nighttime room temperature in non-heating season if no tankless coil is in use.
The temperature/pressure gauge may help in checking for
normal conditions before and during boiler operation.
However the boiler pressure or temperature gauge can be wrong!
This boiler pressure and temperature gauge shows a typical in-boiler pressure of under 20 psi, and a temperature of about 190 °F. (The boiler had just cut off on a heating cycle.)
What Are the Normal Hot and Cold Operating Pressures of Residential Hydronic (hot water) Heating Boilers?
On a residential heating boiler the automatic water-feeder/pressure reducing valve that automatically provides makeup water to the heating boiler if pressure drops below 12 psi. So 12 psi is the typical "cold" pressure for residential boilers.
If your building is taller than two floors, the installer may have needed to boost the starting "cold" water pressure for your boiler to overcome the hot water distribution piping head pressure - otherwise your heating circulators may not be able to circulate hot water.
At PUMP, WATER PRESSURE BOOSTING we explain the relationship between building height and water pressure, and we illustrate the water pressure decrease in building water supply piping with building height. But a look at the basement water pressures in this illustration also explains the pressures that a basement located hot water heating circulator pump has to overcome.
12 psi is for typical U.S. / Canadian residential heating systems normal cold temperature starting pressure. U.K. and european heating systems should be pressurized to between 1 and 1.5 bar - cold.
20 psi is typical for U.S. / Canadian residential heating systems normal hot operating temperature, up to just under 30 psi, depending on the high-limit temperature setting on the boiler limit control. If we set the boiler high-limit much over 210, on many residential systems the system pressure will exceed 30 psi and we'll see water leaking from the pressure/temperature relief valve - ultimately an unsafe condition.
Where & How do I Set Boiler or Furnace Temperature?
Remember that the building THERMOSTATS set the desired temperature in the occupied spaces in building, not the actual temperature in the heating boiler or furnace itself. In most heating systems, turning up the thermostat simply causes the boiler or furnace to turn on. The temperature at the boiler or furnace is controlled by local safety devices mounted right at that equipment.
Hot Water Heating (hydronic) Boiler temperature, pressure setting controls: For details how, to what number, and on what controls the hydronic heating boiler temperatures are set, see AQUASTAT CONTROL Functions, and LIMIT CONTROL, SINGLE.
Steam Boiler Pressure Gauge and Normal Pressure Ranges
Pressure and Temperature gauge on steam heating boilers:
[Click to enlarge any image
Steam heating boiler pressures:
Residential steam heating systemsoperate at very low pressures, perhaps around .5 psi - that' s 1/2 of one psi while commercial steam boilers may operate at higher pressures. For this reason residential steam heating systems are usually designated as low pressure steam boilers.
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 - we provide additional examples and details of steam boiler pressure below.
Commercial high pressure steam boilers operate in higher pressures and temperature ranges depending on the boiler purpose and design. The reason for operating steam boilers at higher pressures is that the efficiency of a steam engine is significantly increased at higher pressures (Sadi-Carnot 1824).
For example the high pressure steam boiler in a locomotive may operate at pressures of 200-250 psi (1.38-1.72 MPa) or even higher. Specially constructed very high pressure steam boilers may operate at pressures over 1,500 psi. - Wikipedia 4/14/14
Watch out: You won't find high pressure steam boilers being used for residential building heating. In fact if you see a residential boiler whose steam pressure has been set over about 0.5 psi most likely there is a problem with the steam distribution system piping or radiators that needs to be addressed.
Steam heating boiler temperatures:
Residential low pressure steam heating boilers, because they produce steam, boil water. So the boiler operating temperatures if measured at the boiler will range between ambient room temperature (no heat is being called for and the boiler has cooled off completely) and boiling temperature which at sea level is 212°F.
Commercial high pressure steam boiler temperatures: because the vaporization point of water at sea level is 212°F that's the normal temperature you'd expect in a steam boiler.
Definition of saturated steam: Saturated steam is steam that is at the same temperature as that of the water from which it is emanating, that is, the stem has not been heated past the boiling point of water that produces it -212°F if we are at sea level and at a normal low heating boiler pressure operating range. The steam produced by a residential steam heating boiler is normally saturated steam. See BLEVE EXPLOSIONS.
Definition of superheated steam: But steam can also become superheated, meaning that it has reached a temperature higher than the boilering point, for example if steam contacts a surface at a temperature higher than its own. Superheated steam becomes more dry, changing its properties as a result.
Definition of dry steam: Steam that has slightly superheated enough to prevent condensation problems (a desired condition in steam engines) is called dry steam.
What Are the Normal Hot and Cold Operating Pressures of Low Pressure Residential Steam Heating Boilers?
Low pressure steam boiler pressure: Low Pressure Residential steam heating systems are almost always designed to operate at very low pressures, typically around .5 psi - that' s 1/2 of one psi or a bit less.
At left if you enlarge the image you'll see that the steam pressure gauge on this Weil McLain Model 68 steam boiler reads about 0.5 psi - a setting consistent with the pressure set and shown on the scale on the steam pressure control to the right of the gauge.
If your residential steam boiler is operating at higher pressures (take a look at the dial setting on your PRESSURE CONTROL, STEAM BOILERS) , 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.
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
Steam radiators tipped the wrong way
Improperly relocated steam piping that has the incorrect slope
Radiator valves that are not operating,
Radiator steam vents that are not operating properly - STEAM VENTS
Do You Need to Replace a Heating Boiler Pressure & Temperature Gauge
Reader Question: How to replace a leaky pressure/temperature gauge on a boiler
... How to I safely drain and refill the water in the boiler to
effect this repair? B - J. Wojciechowski
Please see BOILER GAUGE REPLACEMENT for details on how to replace a hot water or steam boiler pressure or temperature gauge.
Hot Water Heating System Controls Inspection, Peripherals, Key Components
How to determine what type of heating system is installed:
Warm Air Heating Systems - Furnaces: If the heat in your building is provided by warm air that flows out of ceiling, wall, or floor air supply registers into the
occupied space, or if your heating system uses a water-to-air heating system then the air which warms the living space is probably being
delivered through large or small diameter ducts, registers, air filters, and a furnace blower, and the air is being
heated by a gas, oil, or electric furnace, or perhaps by a heat pump or a geo-thermal system.
Hot Water or Steam Heating Systems - Boilers: If the heat in your building is provided by warm or hot metal radiators, heating baseboards containing finned copper tubing, or wall convectors that look like a radiator but contain finned copper tubing, or if heat is provided by flexible rubber, plastic, or metal tubing run in building floors or ceilings, then the warm or hot water circulating in those devices is probably being delivered by piping circulating water heated by a heating boiler, or possibly by a steam boiler or a heat pump or geo-thermal system.
If your heating radiators have valves which hiss and let air escape as heat is coming on your heat is probably being delivered in pipes which circulate steam from the steam boiler up through radiators in the occupied space.
This website provides description of all of the major
components of hot water or steam heating systems, how to recognize or find each component, what it looks like, what goes wrong, and how
to maintain, repair or adjust the component.
Green link shows where you are in this article series.
Question: a few questions about commercial / power plant steam generators
1) How to size the safety valve for a boiler with no stamp?
2) What are the overall conditions responsible for the damage of superheater coils?
3) Why is deaerated water not used in boiler at the time of boiler hydraulic testing?
Size or rating of the pressure/temperature relief safety valve on steam boilers & missing data tags
If the data tag identifying the safety valve has been lost, and considering that this is such an important safety device, and considering the importance of installing a valve of adequate capacity, I'd just replace a valve that was in question for any reason whatsoever. We're talking about a residential part price of $20. U.S. (or less).
In some jursidictions even on residential steam heating boilers and certainly on a commercial or power plant steam generator in particular, I wouldn't be surprised if regulations and maintenance guidelines would view a missing steam boiler pressure/relief valve data tag as a safety violation. Also see RELIEF VALVE, TP VALVE, STEAM BOILER
Superheater coils on steam boilers, sources of damage
I presume you are referring to super heater coils that are used in a steam-heat system boiler to generate saturated steam. The super heater coils are specially used in Boilers of Power plant. These are not residential heating system components, and with respect, are beyond our expertise. In my OPINION an important consideration is to assure that the proper safety pressure/relief valves are mounted at the proper locations and are in good working condition on superheater coils as well. See REFERENCES for superheater coils and super heater coil damage. 
Use deareated water in steam boilers during testing?
That question too is not pertinent to residential steam systems. Deareated water is water used in commercial or power generating boilers from which dissolved oxygen or other gases is removed to avoid corrosion in the system. (Oxygen and other gases are removed during deaeration to a level as low as feasible - it won't quite be to zero. typically oxygen is removed down to about 7ppb during deaeration of water for steam systems. 
OPINION: it may seem reasonable to test a steam generating boiler with deaerated water, arguing that you're trying to duplicate the in-service condition.
However I speculate that
The corrosive effects of a brief hydraulic pressure test of a steam generating system are perhaps very low or even below measurement thresholds, as compared with in-service use water, perhaps moreso if performed at low temperature
The focus in steam generating boiler testing is on pressure tolerance and leak detection over a short interval nothing like the in-service life over which hot water in a steam generating boiler, if not deaereated, would be expected to have very corrosive effects.
Take a look at Steam: Its Generation and Use for details. and see our articles on residential and light commercial steam boilers beginning at STEAM HEATING SYSTEMS.
Ask a Question or Search InspectApedia
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.
 Power Technology and Engineering (formerly Hydrotechnical Construction),
Volume 43, Number 4, 247-250, DOI: 10.1007/s10749-010-0105-4 - Thermal Power Stations, Temperature regime for damaged steam superheater coils, V. A. Bogachev (this is a PDF file - if you can't find contact SpringerLeak)
 "Deaerator", Wikipedia, web search 12/18/11. Quoting: The deaerators in the steam generating systems of most thermal power plants use low pressure steam obtained from an extraction point in their steam turbine system. However, the steam generators in many large industrial facilities such as petroleum refineries may use whatever low-pressure steam is available.
 Babcock & Wilcox Co. (2005). Steam: Its Generation and Use (41st ed.).
 Thomas C. Elliott, Kao Chen, Robert Swanekamp (coauthors) (1997). Standard Handbook of Powerplant Engineering (2nd edition ed.). McGraw-Hill Professional. ISBN: 0-07-019435-1.
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.)
Hills, Richard L. (1989). Power From Steam. Cambridge University Press. p. 203. ISBN 0-521-45834-X.
Roy, G.J. (1975). Steam Turbines and Gearing. Kandy Marine Engineering Series. Stanford Maritime. pp. 36–37. ISBN 0-540-07338-5.
Wikipedia provided background information about some topics discussed at this website provided this citation is also found in the same article along with a " retrieved on" date. NOTE: because Wikipedia entries are fluid and can be amended in real time, we cite the retrieval date of Wikipedia citations and we do not assert that the information found there is necessarily authoritative. High-Pressure steam locomotive, retrieved 4/14/2014 original source: http://en.wikipedia.org/wiki/High-pressure_steam_locomotive
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.