Guide to Setting Heating System Pressure & Temperature Controls
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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?

This website answers most questions about all types of central Heating System r Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.

.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?

Photograph of a multi function combination control on a heating boiler

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.

Hot water heating boiler normal pressure ranges as read on the pressure gauge, are described in this article, below.

The means by which a hot water heating boiler's pressure is set or controlled are described in this article below at Where do I Set the Heating Boiler Operating Pressure?

For details how, to what number, and on what controls the hydronic heating boiler temperatures are set, also see AQUASTAT CONTROL Functions, and Limit Switches, Boilers.

Steam Boiler Temperature & Pressure Settings

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:>

Furnace fan limit switch (C) Daniel Friedman

Warm Air Furnace Temperature Settings

Furnace temperature setting controls: Warm air furnace temperatures are controlled at the FAN LIMIT SWITCH.

See FURNACES, HEATING for a complete discussion of warm air heat.

Additional furnace controls include register and duct dampers - ZONE DAMPER CONTROLS

Hydronic (hot water) Heater Pressure Gauge and Normal Pressure Ranges

Typical location of a boiler gauge 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

LEAKS at BASEBOARD, CONVECTOR, RADIATOR - how to find leaks at baseboards, radiators, etc.
BOILER LEAKS CORROSION STAINS - how to diagnose & evaluate leaks on or in heating boilers
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.
Pressure/temperature relief valves - can also leak on their own - an unsafe condition. See /heat/ReliefValves.htm

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.

The controls in this photo are discussed in more detail at STEAM HEATING SYSTEMS

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

For details about radiator problems see RADIATORS and see LEAKS at BASEBOARD, CONVECTOR, RADIATOR. Also see HEATING LOSS DIAGNOSIS-BOILERS. More about steam boiler gauges is at Steam Pressure Gauge.

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BOILERS, HEATING
  BOILER OPERATION DETAILS
  BOILER CONTROLS & SWITCHES
  Air Bleeder Valves
  Air-bound boilers & radiators
  Air Scoops Purgers Separators
  AQUASTAT CONTROL Functions
  Boiler Pressure Controls & Settings
  CAD CELL RELAY SWITCH
  CHECK VALVES, HEATING SYSTEM
  Chemical treatments, Boiler
  Circulator Pumps & Relays
  ELECTRIC MOTOR OVERLOAD RESET SWITCH
  ELECTRICAL POWER SWITCH FOR HEAT
  Expansion Tanks
  FIRE SAFETY CONTROLS
  Gauges on Heating Equipment
  Limit Switches, Boilers
  Low Water Cutoff Valves, Boilers
  MIXING / ANTI-SCALD VALVES
  OIL LINE QUICK STOP VALVES
  OIL LINE SAFETY VALVES
  Pressure Gauges, Boilers
  Pressure & Temperature Settings, Controls
  RELIEF VALVES - TP VALVES
  Reset Switch - Primary Control
  Reset Switch - electric motors
  SPILL SWITCHES
  STACK RELAYS
  THERMOSTATS, HEATING / COOLING
  Water Feeder Valves, Hydronic Boiler
  Zone Valves

STEAM HEATING SYSTEMS
  AQUASTAT CONTROL Functions
  BACKDRAFTING HEATING EQUIPMENT
  BACKFLOW PREVENTER VALVE, HEATING SYS
  BANGING HEATING PIPES RADIATORS
  CAD CELL RELAY SWITCH
  CHECK VALVES, HEATING SYSTEM
  Chemical treatments, Boiler
  Circulator Pumps & Relays
  COMBUSTION GASES & PARTICLE HAZARDS
  CONDENSATE RETURN PIPES, PUMPS, STEAM
  DIAGNOSE & FIX BOILER
  DRAFT HOODS - gas fired
  DRAFT MEASUREMENT, CHIMNEYS & FLUES
  DRAFT REGULATORS, DAMPERS, BOOSTERS
  ELECTRIC MOTOR OVERLOAD RESET SWITCH
  ELECTRICAL POWER SWITCH FOR HEAT
  EXPANSION TANKS
  FIRE SAFETY CONTROLS
  GAUGES, HEATING EQUIP.
  LIMIT SWITCH, BOILER
  LOW WATER CUTOFF VALVE
  MIXING / ANTI-SCALD VALVES
  PRESSURE, TEMPERTURE SETTINGS, CONTROLS
  PRESSURE SWITCH, STEAM BOILER
  RELIEF VALVES - STEAM TP VALVES
  SIGHT GLASS, STEAM BOILER
  SPILL SWITCHES
  STACK RELAY SWITCH
  STEAM PRESSURE GAUGE
  STEAM TRAPS
  STEAM VENTS
  THERMOSTATS, HEATING / COOLING
  WATER FEEDER Valves, Steam

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

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Carbon Dioxide Gas Toxicity
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Fuel Oil & Oil Heating Magazine, 3621 Hill Rd., Parsippany, NJ 07054, 973-331-9545
Goodman Furnace High Temperature Plastic Vent HTPV safety recall US CPSC notice
Home Heating System Should Be Checked [for proper venting and for CO Carbon Monoxide Hazards - DJF]
Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
Lennox Pulse Furnace Safety Inspection/Warranty Program: Carbon Monoxide Warning
Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
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Weil McLain Model GV Gas Boiler/gas valve CPSC recall/repair
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 Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"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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What Are the Normal Hot and Cold Operating Pressures of Residential Hydronic (hot water) Heating Boilers?

Where & How do I Set Hot Water Boiler, Steam Boiler, or Furnace Temperature?

Hot Water Boiler Temperature Settings

Steam Boiler Temperature & Pressure Settings

Warm Air Furnace Temperature Settings

Hydronic (hot water) Heater Pressure Gauge and Normal Pressure Ranges

Where do I Set the Heating Boiler Operating Pressure?

Residential Steam Boiler Normal Temperature & Pressure Ranges

What Are the Normal Hot and Cold Operating Pressures of Residential Steam Heating Boilers?

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair