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AFUE DEFINITION, RATINGS
AGE of AIR CONDITIONERS & HEAT PUMPS
AGE of HEATERS, BOILERS, FURNACES
AIR CONDITIONING & HEAT PUMP SYSTEMS
AIR FILTERS for HVAC SYSTEMS
AIR HANDLER / BLOWER UNITS
AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE
ANIMAL ALLERGENS / PET DANDER
ANIMAL ENTRY POINTS in buildings
ANIMAL ODORS IN buildings
ANTI SCALD VALVES
ANTIFREEZE for BOILERS
ANODES & DIP TUBES on WATER HEATERS
APPLIANCE EFFICIENCY RATINGS
ASBESTOS IDENTIFICATION IN buildings
BACKDRAFTING HEATING EQUIPMENT
BACKFLOW PREVENTER VALVE, HEATING SYS
BACKFLOW PREVENTER, HEATER WATER FEEDER
BACKUP HEAT for HEAT PUMPS
BANGING HEATING PIPES RADIATORS
BIOGAS PRODUCTION & USE
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BLUE vs YELLOW COMBUSTION FLAMES
BOILER CHEMICAL TREATMENTS
BOILER COMPONENTS & PARTS
BOILER CONTROLS & SWITCHES
BOILER LEAKS CORROSION STAINS
BOILER LEAKS, HOW TO LOCATE
BOILER NOISE SMOKE ODORS
BOILER OPERATING PROBLEMS
BOILER OPERATING STEPS
BOILER PRESSURE & TEMPERATURE SETTINGS
BOOKSTORE - InspectAPedia
BTU USAGE MONITORS
BUILDING SAFETY HAZARDS GUIDE
CAPACITORS for HARD STARTING MOTORS
CARBON DIOXIDE - CO2
CARBON MONOXIDE - CO
CHEMICAL TREATMENTS for BOILERS
CHIMNEY INSPECTION DIAGNOSIS REPAIR
CHIMNEYS & Flues - Asbestos Transite Pipe
CHINESE DRYWALL HAZARDS
CIRCULATOR PUMPS & RELAYS
COOL OFF HEAT, Thermostat Switch
COMBUSTION AIR for TIGHT buildings
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
COMPLETE COMBUSTION, Stoichiometric
CREOSOTE FIRE HAZARDS
Curved Brick Chimneys - Sulphation
CONDENSING BOILERS/FURNACES DAMAGE
CONVECTOR HEATERS - HYDRONIC COILS
DEFINITION of Heating & Cooling Terms
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DIRECT VENTS / SIDE WALL VENTS
DIRECTORY of OIL TANK EXPERTS
DRAFT HOODS - gas fired
DRAFT MEASUREMENT, CHIMNEYS & FLUES
DRAFT REGULATORS, DAMPERS, BOOSTERS
DUCT SYSTEM & DUCT DEFECTS
DUST, HVAC CONTAMINATION STUDY
DUST SAMPLING PROCEDURE
ELECTRIC HEAT, DIAGNOSIS, REPAIR
ELECTRIC MOTOR DIAGNOSTIC GUIDE
ELECTRIC MOTOR OVERLOAD RESET SWITCH
ELECTRICAL POWER SWITCH FOR HEAT
EVAPORATIVE COOLING SYSTEMS
FAN, AIR HANDLER BLOWER UNIT
FAN AUTO ON Thermostat Switch
FAN, COMPRESSOR/CONDENSER UNIT
FAN CONVECTOR HEATERS - HYDRONIC COILS
FAN LIMIT SWITCH
FILTERS, AIR for HVAC SYSTEMS
FILTERS, OIL on HEATING EQUIPMENT
FIRE SAFETY CONTROLS
FIREPLACES & HEARTHS
FLAME COLOR, BLUE vs YELLOW COMBUSTION
FLOODED HEATING EQUIPMENT REPAIR
FLOODED WATER HEATER REPAIR
FLUE VENT CONNECTORS
FREEZE-PROOF A BUILDING
FUEL OIL TYPES & CHARACTERISTICS
FUEL UNIT, HEATING OIL PUMPS
FURNACE CONTROLS & SWITCHES
FURNACE EFFICIENCY, HIGH vs MID
FURNACE HEAT EXCHANGER LEAKS
FURNACE OPERATION DETAILS
FURNACE OPERATING TEMPERATURES
GALVANIC SCALE & METAL CORROSION
GAS BURNER Flame & Noise Defects
GAS FIRED WATER HEATERS
GAS PIPING, VALVES, CONTROLS
GAUGES ON HEATING EQUIPMENT
GEOTHERMAL HEATING SYSTEMS
HEAT EXCHANGER LEAK TEST
HEAT LOSS in BUILDINGS
HEAT LOSS DETECTION TOOLS
HEAT LOSS INDICATORS
HEAT LOSS PREVENTION PRIORITIES
HEAT LOSS R U & K VALUE CALCULATION
HEAT PUMPS, DIAGNOSIS, REPAIR
HEAT TAPES & CABLES on Roofs for Ice Dams
HEATING COST FUEL & BTU Cost Table
HEATING COST SAVINGS METHODS
HEATING LOSS DIAGNOSIS-BOILERS
HEATING LOSS DIAGNOSIS-FURNACES
HEATING OIL CLOUD WAX GEL POINT
HEATING OIL EXPOSURE HAZARDS, LIMITS
HEATING OIL - OLD, USEABLE?
HEATING OIL PIPING TROUBLES
HEATING OIL SHELF LIFE
HEATING OIL SLUDGE
HEATING OIL USAGE RATE
HEATING SYSTEM INSPECTION GUIDE
HEATING SYSTEM NOISES
HIGH EFFICIENCY BOILERS/FURNACES
HOT WATER HEATERS
HOT WATER IMPROVEMENT
INSULATION INSPECTION & IMPROVEMENT
LOW VOLTAGE BUILDING WIRING
LOW VOLTAGE TRANSFORMER TEST
LP & Natural Gas Safety Hazards
MANUALS & PARTS GUIDES - HVAC
MIXING / ANTI-SCALD VALVES
MOTOR OVERLOAD RESET SWITCH
NATURAL GAS COMBUSTION PRODUCTS
NO HEAT - BOILER
NO HEAT - FURNACE
NOISE / SOUND DIAGNOSIS & CURE
NOISE AIR CONDITIONER / HEAT PUMP
NOISE, DUCT VIBRATION DAMPENERS
NOISE, HEATING SYSTEMS
NOISE, WATER HEATER
ODORS GASES SMELLS, DIAGNOSIS & CURE
ODORS FROM HEATING SYSTEMS
OIL BURNER FUEL UNIT
OIL BURNER INSPECTION & REPAIR
OIL BURNER NOISE SMOKE ODORS
OIL BURNER NOZZLE & ELECTRODES
OIL BURNERS, RETENTION HEAD
OIL BURNER SOOT & PUFFBACKS
OIL FILTERS on HEATING EQUIPMENT
OIL FILTER MISSING
OIL FUEL TYPES & CHARACTERISTICS
OIL HEAT FIRE SAFETY CONTROLS
OIL LINE CLOGGING FIX
OIL LINE QUICK STOP VALVES
OIL LINE SAFETY VALVES
OIL FILL PIPE LEAKS
OIL PUMP FUEL UNIT
OIL SPILL CLEANUP / PREVENTION
PLASTIC HEATER VENT
PULSE COMBUSTION HEATERS
PRESSURE REDUCING VALVES
PRESSURE REGULATOR, WATER
PUFFBACKS, OIL BURNER
PUMPS, PONY PUMPS
RADIANT HEAT Floor Mistakes to Avoid
RADIANT HEAT TEMPERATURES
RADIANT SLAB FLOORING CHOICES
RADIANT SLAB TUBING & FLUID CHOICES
BANGING HEATING PIPES RADIATORS
BASEBOARD, CONVECTOR, RADIATOR TYPES
COLD HOT WATER BASEBOARD / RADIATOR
COLD STEAM HEAT RADIATORS
LEAKS at BASEBOARD, CONVECTOR, RADIATOR
RADIATOR BASEBOARD or CONVECTOR COVERS
RADIATOR or CONVECTOR INSULATION
RADIATOR STEAM VENTS
RADIATOR STEAM VENTS, AUTOMATIC
Install Steam Vents to Control Heat
RADIATOR VALVES & HEAT CONTROLS
Manual Radiator Valves
Hot Water vs Steam Radiator Valves
Adjust Level of Heat
Automatic Radiator Valves
UNEVEN HEAT DIAGNOSIS
RELIEF VALVE LEAKS
RELIEF VALVES - TP Valves on Boilers
RELIEF VALVES - STEAM TP VALVES
RELIEF VALVES - Water Heaters
RELIEF VALVES - Water Tanks
Reset Switch - Heater Primary Control
Reset Switch Broken - Quick Repair
RESET SWITCH - ELECTRIC MOTOR
Reset Switch - Stack Relays
SAFETY HAZARDS & INSPECTIONS
SAFETY HAZARDS GUIDE
SAFETY, HEATING INSPECTION
SAFETY RECALLS CHIMNEYS VENTS HEATERS
SOOT on OIL FIRED HEATING EQUIPMENT
SPILL SWITCHES - Flue Gas Detection
SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS
STACK RELAY SWITCHES
STEAM HEATING SYSTEMS
Thermal Expansion Cracking of Brick
THERMAL EXPANSION of HOT WATER
THERMAL EXPANSION of MATERIALS
THERMAL IMAGING, THERMOGRAPHY
THERMAL IMAGING MOLD SCANS
THERMAL MASS in BUILDINGS
THERMAL TRACKING & HEAT LOSS
THERMOSTATS, HEATING / COOLING
THERMOSTATS, WATER HEATER
THERMOSTATIC EXPANSION VALVES
TRANSITE PIPE CHIMNEYS & FLUES
VIDEO GUIDES: Heating System Videos
VIDEO GUIDES - InspectAPedia.com
WATER HEATER SAFETY
WATER HEATERS for HOME HEATING USE?
WATER HEATER NOISES
WATER HEATER SCALE - De-Liming Procedure
WATER HEATER SCALE PREVENTION
WINTERIZE A BUILDING
WOOD, COAL STOVES & FIREPLACES
WOOD STOVE SAFETY
Steam vents on heating systems: here we provide an inspection and repair guide to the vents found on radiators and piping used with Steam Heating Systems.
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This article series answers most questions about central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.
Also see RADIATOR STEAM VENTS, AUTOMATIC wHere we explain automatic steam vents and heat regulation using air vents on steam radiators. If you don't know what kind of heat your building uses, we explain how to figure out the answer at HEATING SYSTEM TYPES. If your heating system is not working properly, see NO HEAT - BOILER or NO HEAT - FURNACE.
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 COMPONENTS & PARTS 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.
Our photo (above left) shows a common model of automatic air bleed valve used on residential steam heat radiators.
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.
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 on individual radiators or main steam vents may not be opening when they should. If an individual steam radiator vent fails to open, that radiator won't get hot even though its supply valve is open.
But if a main steam vent (master steam vent) is not opening, the whole heating system may continue to work, but we expect to see two problems:
It is normal for steam vents to make a hissing noise (also described as a whistling noise) at the start of a heating cycle while air is being vented out of the steam piping or steam radiator as it is pushed by rising steam.
Watch out: If the radiator continually makes noises (hissing, whistling or wheezing) at the steam vent, there is a problem that needs to be fixed: a bad steam vent, steam piping problem, steam pressure set too high, or boiler oversized for the heating distribution system.
First, make sure that the noise complaint is coming from the steam vent and not from water hammer or clanking steam piping.
Next: mineral deposits or dirt in a steam vent can prevent it from opening or closing properly. While it is often possible to disassemble and clean (soak in vinegar) a mineral-clogged steam vent, other internal vent failures can also occur, so considering the low cost of replacement steam vents, it usually makes sense to simply replace the steam vent entirely. At RADIATOR STEAM VENTS, AUTOMATIC we list a variety of replacement steam vents.
A rattling sound at a steam vent may be heard at any radiator or at a main steam riser where a main line vent is installed. If your steam vent is rattling an internal part has become loose. Replace the vent.
Also see these noise and sound control articles:
BANGING HEATING PIPES RADIATORS for details about heating pipe noise cause and cure.
HEATING SYSTEM NOISES - lists heating system noise types, sources, problem indicators, cures
If water is "spitting" out of your steam radiator's air vent it's most likely that debris, sediment, mineral deposits, or rust flakes have partly clogged the air vent. Steam experts such as Dan Holohan suggest that you may be able to clean a spitting or partly-clogged steam vent by disassembling and boiling the vent in vinegar (to dissolve minerals).
Watch out: don't remove a steam vent when the heating system is in use or hot. You can get badly burned. But some specialty steam vents (air valves) such as the Hoffman Model 508 (Part No. 401475) can be disassembled and cleaned without removing from the line.
If a lot of water is really leaking out of a steam radiator's steam vent, the radiator may also have become waterlogged (according to some writers). We don't think this is a common problem, since most steam vents are mounted at mid radiator height or higher - the radiator would have to be really full of condensate for a lot of water to be coming out of the steam vent - unlikely. See BANGING HEATING PIPES RADIATORS wHere we explain steam condensate return problems that can cause banging clanging pipes.
If a steam radiator contains condensate (water from condensed steam) that fills the radiator to a level above the steam vent, the steam vent cannot function, air won't be pushed out of the radiator by rising steam, and the radiator won't heat.
If your steam vent is mostly venting steam but spits a few drops of water, the vent may not be working properly and may need replacement, but it is not as likely to be a sign that the steam system has become waterlogged.
Watch out: as we discuss at BANGING HEATING PIPES RADIATORS, if your heating boiler does not have an automatic water feeder and you've been putting makeup water into the boiler manually, a blocked condensate line and low water in the boiler will eventually lead to total loss of heat when the low water cutoff switch (see LOW WATER CUTOFF CONTROLS) , a key boiler safety device, simply shuts down the boiler.
Watch out: are you sure your system is using steam heat? Hot water radiators often include a manual air-bleeder valve that must be opened to let air out of the hot water (not steam) radiator or the radiator won't heat. On a hot water (hydronic) heating system if you leave the air bleeder valve open after air has stopped coming out, indeed water will come squirting out of the valve - indefinitely. Don't do this. See AIR BLEEDER VALVES for details.
Automatic and thermostatically operated steam vents used to provide room temperature control are discussed in detail also at RADIATOR VALVES & HEAT CONTROLS.
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