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Here we provide an inspection and repair guide to the vents found on radiators and piping used with Steam Heating Systems. You will also see that this website answers most questions about central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.

If you don't know what kind of heat your building uses, see our introduction at BOILERS, HEATING. If your heating system is not working properly, see NO HEAT - BOILER / FURNACE DIAGNOSIS.

Because some controls are used in common on hot water heat, hot air heat, and steam boilers, readers should see these other articles: If your building uses forced hot water heat see BOILER CONTROLS & SWITCHES. Some of those controls also appear on steam heating equipment. Also see BOILER PARTS LIST for a detailed list of heating boiler controls, other heating system components, parts such as circulator pumps & draft regulators If your building uses warm air heat see FURNACE CONTROLS & SWITCHES. See ELECTRICAL POWER SWITCH FOR HEAT.

Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Guide to Steam Vents on Residential Heating Systems

Our photo (left) shows a common model of automatic air bleed valve used on residential steam heat radiators.

How Steam Vents Work on Steam Heating Systems

At the start of a heating cycle as steam rises in the building steam pipes and begins to enter the heating radiator, air in the cool radiator is pushed out through this valve.

As the radiator gets warm, then hot due to the rising steam, a mechanical thermostatically operated valve inside of the air vent, also called a steam vent, closes the vent so that steam does not continue to escape.

Diagnosing Hissing Sounds at Steam Radiators

It is normal to hear a hissing sound from the steam vent as air escapes from the radiator at the start of a heating cycle.

The hissing sound should stop and the valve close when the radiator gets hot.

Steam Vents that Do Not Shut Off When They Should

Steam Vents that Do Not Open When They Should

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

STEAM HEATING SYSTEMS
  Cad Cell Relay Switch Flame Sensors
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
DEFINITION of Heating & Cooling Terms
DRAFT HOODS - gas fired
DRAFT REGULATORS - barometric dampers
  Cad Cell Relay Switch Flame Sensors
  Circulator Pumps & Relays
  Draft Regulators, Dampers
  Expansion Tanks
  Gauges on Heating Equipment
  Limit Switches, Boilers
  Low Water Cutoff Valves, Boilers
  Mixing Valves
  Relief Valves - TP Valves
  Sight Glass, Steam Boiler
  Pressure Switch, Steam Boiler
  Spill Switches
  Stack Relay Switch
  Steam Pressure Gauge
  Steam Vents
  LOW WATER CUTOFF CONTROLS
  WATER FEEDER VALVES

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..

• Hot Water Heating Boiler Operating Details - 39 Steps to Hot Water Heating Success
• Air Bleeder Valves for Hot Water Heating Systems: Radiators, Baseboards, Convectors
• Aquastats Heating Boiler Primary Controls: A guide to Aquastats for control of hot water heating boilers and tankless coils
• Cad Cell Relays 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
• Gauges for Temperature & Pressure: Guide Temperature & Pressure Gauges on Hot Water or Steam Heating Boilers
• Low Water Cutoff Controls: Guide to LWCOs on hot water heating systems
• Mixing Valves: Guide to mixing valves on hot water heating systems and radiant heat systems
• Oil Burners: Guide to Oil Burners for heating systems, boilers & Furnaces: basic parts, operation, maintenance, performance & money-saving tips
• Oil Tanks: Guide to Heating Oil Underground & Above ground Oil Storage Tank Leaks, Testing, Problems & Solutions, Home Buyer's / Home Owner's Guide
• Oil Piping: A guide to heating oil piping, valves, controls, leaks, repairs for heating systems
• Parts & Components Guide for Heating Boilers: How to Identify the Components of Hot Water Heating Boilers - A Guide to Hydronic Heating System Parts
• Relief Valves - TP Valves: A guide to temperature and pressure relief valves & safety controls on hot water and steam heating systems
• Stack Relay Switches: Guide to finding, resetting, maintaining stack relays on oil fired furnaces or boilers as flame sensors & safety devices
• 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

More Information on Building Diagnostic Inspections and Repairs

• Carbon Dioxide Gas Toxicity
• Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
• Dust from HVAC? An Investigation of Indoor Dust Debris Blamed on a Heating/Cooling System Reveals Carpet Dust
• 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
• Oil Tanks Above Ground, UL Standards, guidance for home owners, buyers, and inspectors
• Plastic Heating Vent Pipe & Other Heating Safety Recall Notices
• 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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