Photo Guide to Steam Heating Controls & Gauges InspectAPedia® -
What are the various gauges, switches, & controls found on residential steam heating systems?
How can I identify, inspect, and use controls and gauges on residential steam heating systems?
Steam heating system low water cutoff, water feeders
Pressure and Temperature Gauges on Steam Heating Boilers - Troubleshooting & Repair Guide
Hartford loop & other safety controls found on steam systems
Steam heat condensate return pump systems & controls
Questions & answers about residential steam heating system controls, valves, gauges
This article series provides an illustrated inspection and repair guide to Steam Heating Systems. This website answers just about any question you may have about central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.
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Types of Controls Found on Residential Steam Heating Systems
All of the steam heating system controls described in our introduction are illustrated below and described in greater detail in individual articles found in this steam heat series.
Sketch of a one-pipe typical steam heating system (left) is provided courtesy of Carson Dunlop Associates. In a one pipe system each radiator is served by a single pipe: steam rises into the radiator and condensate (water) returns from the radiator through the same pipe loop, as you can see at left.
A two-pipe steam heating system is similar but provides a separate loop of piping that collects condensate and returns it from the radiator to the boiler.
Controls found on Steam Heating Systems
If your heating system looks like a heating boiler but 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.
Although both hot water - hydronic heating systems (discussed at BOILERS, HEATING) and steam boilers (discussed here at STEAM HEATING SYSTEMS) use a boiler that heats water, the heat distribution method and most of the heating boiler controls are different between these two systems.
Both steam boilers and hot water boilers may share certain controls that monitor and manage the heating source such as an oil burner or gas burner. Heater burner controls make sure that there is a safe proper combustion flame, control draft, and protect against flue gas spillage. Examples include the CAD CELL RELAY SWITCH (oil burners) or Spill Switches (gas burners).
Steam Boiler pressure controls:
Because the operating temperature, pressure, and form of heat distribution are different from hot water heat (typically 20-30 psi of hot water), steam boilers (typically less than 0.5 psi steam) use use controls that monitor steam pressure (Pressure Switch, Steam Boiler) shown at left as well as RADIATOR STEAM VENTS (shown later in this article) and other steam piping controls.
And because all steam heating systems consume some water during every heating cycle, steam boilers carefully monitor the water level in the boiler (Low Water Cutoff Valves, Boilers) and require that water be added either manually (now rare, but found on some older steam systems) or automatically (Water Feeder Valves, Steam).
These and other steam controls are illustrated below.
Five Common Safety Devices on a Steam Heating Boiler
The sight glass described just below is just one of the safety devices found on a steam boiler, which will also include
a pressure/temperature relief valve, almost always a
low water cutoff valve,
a Hartford Loop (to prevent loss of water out of the boiler by siphoning out of boiler water from a piping leak), and on many modern residential steam systems, an
automatic water feeder valve may also be installed.
Photo Guide to the Steam Boiler Sight Glass
The sight glass on a steam boiler is an important safety and operating device since it allows the homeowner or inspector to see at a glance when the steam boiler is low on water.
Steam systems use varying amounts of water.
Unlike a hydronic heating boiler, some of the water in the steam boiler is lost through the building's radiator steam vents at each heating cycle.
Just how much water the steam boiler will lose varies widely depending on a number of factors.
But if a heating boiler loses its water without also being shut down it will certainly be damaged by the heat of the oil or gas burner (or coal or wood), and it could lead to a dangerous explosion or fire.
If your steam boiler has an automatic water feeder, you should still check the water level (and clarity) in the sight glass frequently, but the risk of a ruined boiler from lost water is of course much less.
Photo Guide to the Steam Boiler Pressure Control Safety Switch
The pressure control switch on a steam heating boiler is designed to shut the heating system down should unsafe high pressures develop.
As we repeat at our description of pressure gauges on a steam boiler, 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.
Photo Guide to Steam Boiler Low Water Cutoff Valves
Here's a photo of a low water cutoff safety valve LWCO on a steam boiler. This valve on a steam heating boiler needs to be flushed clean weekly (more or less) during the heating season. The yellow handle you see in the photo is used for that purpose.
More photos and details about low water cutoff valves on steam boilers can be read at LOW WATER CUTOFF CONTROLS
Photo Guide to Steam Boiler Automatic Water Feeders
Above are photographs of a couple of different but still modern automatic water feeder valves on a steam boiler.
Here we show the "manual feed" button which can be found on the automatic water feeder in the photo at above left.
Low pressure steam boilers still require a pressure/temperature safety relief valve. However the valve operates at different temperatures and pressures than found on a hydronic (hot water heating) boiler. Residential steam boilers typically operate at below 1 psi.
Guide to Steam Vents on Residential Heating Systems
Details about the inspection, repair, replacement, function, and identification of steam vents on one pipe and two pipe steam heating systems can be read at Steam Vents
Also see RADIATORS for more extensive information about steam radiator troubleshooting.
Guide to Condensate Return Pumps & Condensate Systems on Residential Steam Heating Systems
Our photo at above left illustrates a steam condensate return pump system in a home
Our second steam condensate return system (above right) shows the reservoir and condensate pump motor (grey pump and new piping on the right side of the condensate reservoir at the left in that picture). This system also includes chemical injection into the steam condensate.
Steam Boiler Pressure Gauge and Normal 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.
Details about gauges on heating equipment can be read at GAUGES ON HEATING EQUIPMENT and see Pressure Gauges, Boilers for more details about pressure gauges on hydronic (hot water) heating boilers (these are not steam systems).
Questions & Answers regarding this article
Questions & answers about residential steam heating system controls, valves, gauges
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Additional technical contributors & reference sources for this article are listed below.
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For details about the controls, components and switches commonly found on hot water heating systems see the articles listed below in which we explain how to identify, set, re-set, repair, replace, or avoid problems with the components of a hot water heating system..
BLUE vs YELLOW COMBUSTION FLAMES - the Blueray history and blue flame vs. yellow flame combustion, flame color & combustion efficiency, & how oil competes with gas as a heating fuel.
CAD CELL RELAY SWITCH on oil fired furnaces or boilers as flame sensors & safety devices
Check Valves Guide to check valves and backflow preventers on hydronic (hot water) heating systems (gas or oil fired)
Circulator Pumps Guide to circulator pumps and circulator relays on hydronic (hot water) heating systems (gas or oil fired)
Draft Hoods on gas fired heating equipment, function and safety
Draft Regulators & barometric dampers on oil fired heating equipment
Electrical Power Switches: Where to Turn On or Off Heaters for Furnaces & Boilers, Heat Pumps or Electric Furnaces or Air Conditioners
Expansion Tanks Guide to pressure control and expansion tanks on hydronic (hot water) heating systems (gas or oil fired)
Flue Gas Spill Switch on gas fired heating equipment sense combustion and protect from blocked flues
Gas Piping, Valves, Controls: Guide to LP and natural gas meters, valves, tanks, piping, gas leaks, gas regulator assembly & other gas controls
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, (see next item in this list). ITT Fluid Technology,
1133 Westchester Avenue
White Plains, NY 10604,
tel +1 914 304 1700 fax +1 914 696 2950 www.ittfluidbusiness.com
Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
TANKLESS COILS: A Guide to tankless coils used to produce domestic hot water on heating boilers: hot water quantity, safety, temperature control, leaks, corrosion, repairs
Thermostats & Heat Controls for furnaces & boilers, oil & gas fired, heat pumps or electric furnaces or boilers
Water Feed Valves: A guide to water-feeding/pressure-reducing valves on hot water and steam heating systems
Zone Valves: A guide to zone valves for heating zone control on hot water heating systems
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.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book 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. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
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.)
Links to our list of additional information on heating system inspection, repair, maintenance
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