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AFUE DEFINITION, RATINGS
AGE of HEATERS, BOILERS, FURNACES
BACKDRAFTING HEATING EQUIPMENT
BACKFLOW PREVENTER VALVE, HEATING SYS
BANGING HEATING PIPES RADIATORS
BOILER CONTROLS & SWITCHES
BOILER LEAKS CORROSION STAINS
BOILER NOISE SMOKE ODORS
BOILER OPERATING PROBLEMS
BOOKSTORE - InspectAPedia
BTU USAGE MONITORS
CHEMICAL TREATMENTS for BOILERS
CHIMNEY INSPECTION DIAGNOSIS REPAIR
CIRCULATOR PUMPS & RELAYS
DEFINITION of Heating & Cooling Terms
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DRAFT MEASUREMENT, CHIMNEYS & FLUES
DRAFT REGULATORS, DAMPERS, BOOSTERS
FILTERS, OIL on HEATING EQUIPMENT
FIRE SAFETY CONTROLS
FLOODED HEATING EQUIPMENT REPAIR
FLUE VENT CONNECTORS
FREEZE-PROOF A BUILDING
FUEL OIL TYPES & CHARACTERISTICS
FUEL UNIT, HEATING OIL PUMPS
GAS BURNER Flame & Noise Defects
GAS PIPING, VALVES, CONTROLS
GAUGES ON HEATING EQUIPMENT
HEATING COST SAVINGS METHODS
HEATING LOSS DIAGNOSIS-BOILERS
HEATING OIL PIPING TROUBLES
HEATING SYSTEM INSPECTION GUIDE
HEATING SYSTEM NOISES
HIGH EFFICIENCY BOILERS/FURNACES
LP & Natural Gas Safety Hazards
MANUALS & PARTS GUIDES - HVAC
MOTOR OVERLOAD RESET SWITCH
NO HEAT - BOILER
NOISE, HEATING SYSTEMS
ODORS FROM HEATING SYSTEMS
OIL PUMP FUEL UNIT
PUFFBACKS, OIL BURNER
RELIEF VALVES - STEAM TP VALVES
Reset Switch - Heater Primary Control
RESET SWITCH - ELECTRIC MOTOR
Reset Switch - Stack Relays
SAFETY, HEATING INSPECTION
SAFETY RECALLS, Chimneys, Vents, Heaters
SOOT on OIL FIRED HEATING EQUIPMENT
SPILL SWITCHES - Flue Gas DetectionS
STACK RELAY SWITCHES
STEAM HEATING SYSTEMS
THERMOSTATS, HEATING / COOLING
VIDEO GUIDES: Heating System Videos
Guide to steam heat radiator piping connections: this article describes the piping connections for steam heating radiators. We explain the difference between one pipe and two pipe steam heating systems. We illustrate upfeed steam pipes, downfeed steam pipes, and we make clear how to figure out what type of steam heat is installed in a building - insofar as the steam heat distribution is concerned. We explain how steam rises or enters radiators and how condensate in a steam radiator gets back to the steam boiler. We also describe antique vacuum / vapor steam heat systems. Our page top sketch, adapted from ITT's The Steam Book, shows piping connections for a one pipe steam heating radiator.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Question: where do steam pipes enter steam radiators: top, bottom, or both?
I had a question about the article at RADIATOR VALVES & HEAT CONTROLS.
I’m looking at the sub-section “Types of Radiator Valves: Hot Water vs. Steam” and here is a copy of the 1st paragraph; the writing becomes nonsensical and near the end and it may turn out that some of the information is [was - we've fixed it] incorrect: “In our photo at left you can see not only the radiator control valve, but lots more information: we can conclude that this is a hot water heating system, not a steam heat system because first, the valve is mounted at the top of the radiator (water, not steam - steam enters at a radiator bottom but sometimes so does not water; the reverse is never true).”
Photo at above-left illustrates a two pipe steam heating radiator installed at Vassar College. The control shown on the inlet end at the upper right of the radiator is a No. 8 / 3000-2 Piston Operator from Johnson Service Company, Milwaukee, now Johnson Controls. 
I was trying to make sense of what was written and discovered another article (which also has nonsensical syntax- it must be hard to describe these hot water and steam heating systems) which seems to indicate that in fact steam DOES often enter a radiator at the top.
At this point I am just lost. We don’t have many residential systems with radiator systems (steam or hot water) so I am trying to edumacate myself but don’t have anything in front of me to compare what I think I understand.
I am totally reliant on clear, logical, linear and detailed examples which your site usually has in abundance (thank you by the way.) Here is the link to that other article (refer to the 5th question/answer pairing): oiltechtalk.com/pages/cast_iron.htm
Kind Regards, -Doug
Up-feed - Down-feed, One-pipe - Two-Pipe Steam Piping & Radiators - What's the Difference?
Doug, the other page (not at InspectApedia) that you gave provides information from Dan Holihan  - Dan is probably the most-expert fellow alive when it comes to steam heating systems. Dan's text to which you refer includes these two statements:
Up-Steam Pipe Feed Direction: Down-feed vs Up-Feed: Two Pipe Steam Heat Radiator Connections
One Pipe Steam Radiator Piping Connections
Wet Return vs Dry Return Steam Piping on One Line Steam Heat Systems
The number of steam radiator piping arrangements is quite large, I'm not showing all of the 20+ configurations commonly listed, though I can do so if there is a need.
Wet Return Line Steam Piping
The one pipe steam heat radiator and piping shown at left is connected to an overhead steam suppy main and uses a wet return - condensate flows in the return line. 
Dry Return Line Steam Piping
At left is a one pipe steam radiator connected with a dry return line.
Indeed there is a wide range of both hydronic and steam radiators. A reasonable approach would be to
Some older steam systems, less likely to be encountered now were a vapor/vacuum design, now considered obsolete with oil and gas-fired heating equipment, but you may still encounter piping in older buildings built before or at the time when vapor/vacuum steam systems were being installed.
Vacuum steam heating systems are all two-pipe systems, but include a mechanical vacuum pump at the end of the condensate return piping system.
Vapor / Vacuum steam systems could be designed as either a one-pipe or two-pipe steam heating system and look much like modern steam heating systems but a vapor/vacuum steam system used special air vents to eliminate air from the heating pipes and system.
Vapor steam systems (just to add to the confusion) run at very low pressure but never at a vacuum. These systems used an oversized steam supply pipe to provide nearly-constant flow of steam vapor.
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