Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
AIR CONDITIONING & HEAT PUMP SYSTEMS
BACKDRAFTING HEATING EQUIPMENT
BACKUP HEAT for HEAT PUMPS
BANGING HEATING PIPES RADIATORS
BLOWER FAN OPERATION & TESTING
BOOKSTORE - InspectAPedia
BTU USAGE MONITORS
CARBON MONOXIDE - CO
CIRCULATOR PUMPS & RELAYS
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DIRECT VENTS / SIDE WALL VENTS
DRAFT HOOD, GAS HEATER
DRAFT REGULATOR, DAMPER, BOOSTER
DUCT SYSTEM & DUCT DEFECTS
ELECTRIC MOTOR DIAGNOSTIC GUIDE
FAN, AIR HANDLER BLOWER UNIT
FLOODED HEATING EQUIPMENT REPAIR
FLUE SIZE SPECIFICATIONS
GAS BURNER FLAME & NOISE DEFECTS
GAS PIPING, VALVES, CONTROLS
GEOTHERMAL HEATING SYSTEMS
HEAT PUMPS, DIAGNOSIS, REPAIR
HEATING COST SAVINGS METHODS
HEATING OIL PIPING TROUBLES
HEATING OIL TANKS
HEATING SYSTEM NOISE DIAGNOSIS
HEATING SYSTEM TYPES
GAS LP & NATURAL GAS SAFETY HAZARDS
MANUALS & PARTS GUIDES - HVAC
MIXING / ANTI-SCALD VALVES
MOTOR OVERLOAD RESET SWITCH
NOISE, HEATING SYSTEMS
ODORS FROM HEATING SYSTEMS
OIL FILTERS on HEATING EQUIPMENT
OIL FILL PIPE LEAKS
OIL SPILL CLEANUP / PREVENTION
PLASTIC PLEXVENT ULTRAVENT RECALL
PUFFBACKS, OIL BURNER
RELIEF VALVE LEAKS
RESET SWITCH, HEATER PRIMARY CONTROL
RESET SWITCH, ELECTRIC MOTOR
RESET SWITCH, STACK RELAY
SAFETY, HEATING INSPECTION
SAFETY RECALLS CHIMNEYS VENTS HEATERS
SOLAR HEATING SYSTEM DESIGNS
SOOT on OIL FIRED HEATING EQUIPMENT
STEAM HEATING SYSTEMS
THERMOSTATS, HEATING / COOLING
VIDEO GUIDES: HEATING SYSTEMS
WINTERIZE A BUILDING
WOOD-OIL COMBINATION HEATERS
WOOD STOVE OPERATION & SAFETY
ZONE VALVES, HEATING
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.
Green links show where you are. © Copyright 2015 InspectApedia.com, All Rights Reserved.
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.
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.
For more diagnostic aid on finding the cause and executing the cure of abnormal heating boiler pressures see
Pressure and Temperature gauge on steam heating boilers:
[Click to enlarge any image
Steam heating boiler pressures:
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.
Steam heating boiler temperatures:
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
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.
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.
See STEAM HEATING SYSTEMS .
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.
Frequently Asked Questions (FAQs)
Question: a few questions about commercial / power plant steam generators
1) How to size the safety valve for a boiler with no stamp?
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
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.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References