Guide to Setting Heating System Pressure & Temperature Controls InspectAPedia® -
Heating System Pressure and Temperature Controls
What are normal hot water heat pressure & temperature settings ?
What are normal residential steam heat pressure & temperatures ?
Where & how do I set the boiler pressure & temperature controls?
Where & how do I set a steam boiler pressure & temperature?
Where & how do I set the furnace temperature control?
Troubleshooting heating system boiler controls & switches
Questions & answers about heating system operating pressures, temperatures, and controls for hot water and hot air heating systems and for warm air furnace systems
Here we explain where and how and to what numbers the pressure & temperature are set or controlled on hydronic heating boilers. We also describe where and how the pressure & temperature is controlled on residential steam boilers. We include notes and links to detailed articles about the operation and use of controls on boilers, furnaces, and water heaters.
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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.
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.
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.
Where & How do I Set Hot Water Boiler, Steam Boiler, or Furnace Temperature?
Hot Water Boiler Temperature Settings
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, such as the heating boiler Aquastat shown at left.
Steam boiler temperature, pressure setting controls: For details how, to what number, and on what controls the steam boiler pressure settings and pressure readings are set see:>
Additional furnace controls include register and duct dampers - ZONE DAMPER CONTROLS
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.
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.
Typical operating temperature
settings on a boiler call for a Low temperature (boiler cut-in) between 120 and 160 degF.
Typical operating temperatures on a hydronic boiler call for a high temperature (boiler cuts off) of 180-200 degF.
If we set the boiler upper temperature too high over 200 degrees F. we're at risk of spilling at the pressure temperature relief valve. If we set the boiler upper limit too low, there may be no relief valve problem but under some conditions we may reduce the operating efficiency of the boiler and heating system, thus increasing heating costs. See AQUASTAT CONTROL Functionsfor details.
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 gauge can be wrong!
This gauge shows a typical in-boiler pressure of under 20 psi, and a temperature of about 190 degF. (The boiler had just cut off on a heating cycle.)
For more diagnostic aid on finding the cause and executing the cure of abnormal heating boiler pressures see
BOILER LEAKS, HOW TO LOCATE - how to determine that a boiler or hot water system is leaking and how to find hidden leaks
Expansion Tanks - if the expansion tank is waterlogged, the boiler and hot water heating system pressures will become excessive and spillage may be found at the pressure/temperature relief valve.
Where do I Set the Heating Boiler Operating Pressure?
The operating pressure of a heating boiler (hot water or hydronic heat) is read at the pressure and temperature gauge (see above) and controlled by
The starting or "cold water" pressure at the boiler - typically at 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. Most heating boilers are provided cold makeup water through a pressure-reducing, back-flow preventing, automatic water feeder valve - see Water Feeder Valves, Hydronic Boiler. The valve is adjustable but should not be changed except by a trained heating service technician.
The ending or "hot water" temperature at the boiler - typically 180 deg F to 210 deg F, controlled by the heating boiler's combination control, aquastat, or limit control - see AQUASTAT CONTROL Functions and see Limit Switches, Boilers.
Heating equipment has multiple safety controls designed to prevent damage to the equipment or unsafe conditions. Indirectly, or in emergency, the heating boiler pressure is limited by first, the high limit set on the Aquastat or Limit Switch. If these controls fail, the boiler's temperature and pressure are released by one or more RELIEF VALVES - STEAM TP VALVES
The building THERMOSTATS do not normally directly control the temperature or pressure in the heating boiler. The thermostat sets the desired temperature in the building, but to the heating boiler it is working as a simple "on" - "off" switch, turning the boiler "on" until the thermostat is satisfied (the building is warm enough), then turning the boiler "off".
Residential Steam Boiler Normal Temperature & 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.
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 degF.
The steam boiler pressure is controlled by the Pressure Switch, Steam Boiler - the gray box shown in our photo at left and in closeup at our photo, below.
What Are the Normal Hot and Cold Operating Pressures of Residential 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. 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 (take a look at the dial setting on your Pressure Switch, Steam Boiler) , 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
Questions & answers 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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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
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.)
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Pressure and Temperature gauge on hot water or hydronic heating boilers: this gauge displays the heating boiler internal pressure and temperature.
