Steam Heat Radiator Pipe Connections & Types
Definitions of one pipe vs two pipe steam heat, upflow vs downflow steam distribution, vacuum/vapor steam systems &c

STEAM RADIATOR PIPING CONNECTIONS - Piping.php
CONDENSATE RETURN PIPES, PUMPS, STEAM - separate article
HARTFORD LOOP - separate article
Questions & Answers about steam radiator piping, one pipe vs two pipe, upfeed vs downfeed, and other piping questions
References

Click to Show or Hide Related Topics

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

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.[14]

Steam Radiator Piping Connections & Definitions

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. [22]

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 [1] - 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:

Two Pipe steam radiator (C) Daniel Friedman

Older steam radiators have nipples across just the bottom portion of the sections. This is because steam is lighter than air. When the steam enters the bottom of a radiator (as it always will in a one-pipe steam radiator), it flows upward into the sections, displacing the air as it goes.
Two-pipe steam systems usually have the steam entering through a pipe at the top of the radiator. [1]

Mr. Holihan is a steam heat expert - I absolutely defer to Dan, but I'm not sure that the word usually in the Dan H's second statement can be taken to mean always. [1][12][16][17]

Most two-pipe steam heat radiators will indeed show up with the steam entering the radiator at one end at the radiator top (photo at left), and the condensate return will exit at the bottom of the radiator at its opposite end.

We do on occasion find a two pipe steam system with both steam in and condensate out connections at the radiator bottom, and for sure, all one pipe steam radiators are fed with a pipe connection to the bottom of the radiator.

All one pipe steam heat radiators are fed from the radiator's bottom at one end - as we explain and illustrate later in this article.

At above left is a top-fed two pipe steam radiator at Google Headquarters in New York City.

Two pipe bottom feed steam radiator (C) Daniel Friedman

Steam to Water Radiator Conversions

At left is a bottom-feed (two pipe) hot water (not steam) heating radiator. What's interesting about the radiator at above right is that it was converted to hot water heat from prior two-pipe steam heat.

Notice that crazy location of the air bleed valve (circled in blue) on the left side of the radiator? That's where a steam vent used to mount. You'll have a heck of a time getting all of the air out of this radiator now that it's converted to hot water - at least not through that bleeder.

This was originally a two pipe top-fed steam radiator when it was first installed. A steam vent worked correctly in the location we show and where now an air bleeder (for hot water heat) has been installed. This won't work. On a hot water heating radiator we need the air bleed to be at the top of the device - where the air will be.

In clarifying what we are talking about here I will include some sketches from ITT's now antique Steam Book. [14]

Up-Steam Pipe Feed Direction: Down-feed vs Up-Feed: Two Pipe Steam Heat Radiator Connections

First let's clear up the direction from which steam is being fed into a steam radiator:

Downfeed Steam Risers Entering at Radiator Top

Yes of course Dan is right that there absolutely are also "downfeed steam risers" on some two pipe steam systems (sketch at left).

These "downfeed steam risers" (sounds like an oxymoron) push steam into the radiator from a valve entering at the top

Sketch at left - ITT [17]

Downfeed steam piping that enters at a radiator top will always be two-pipe steam heat systems and the condensate return will always be take off of the bottom of the radiator.[14] . Shown in the ITT sketch are Hoffman Traps. A steam trap, check valve or other device is required on two pipe steam systems to keep steam from entering the condensate return line.

In very early steam systems radiator sections were connected (to permit steam flow) only across the radiator bottom. Steam entering a steam radiator at its top would have been forced down through that radiator section and through bottom nipple connections into the remaining radiator sections. Holohan points out that two-pipe steam designs became common in the U.S. around 1905 and made use of hot water radiators whose sections are connected to permit [more rapid] heat flow through nipples at both top and bottom of each radiator section.[1]

Conversely, hot water radiators are usually connected by nipples at each radiator section top and bottom.

Up-feed Steam Risers Entering at the Radiator Top

There are also upfeed steam pipe systems that may feed into the steam radiator at its top - through a Hoffman Supply Valve (sketch at left - ITT).

These systems will also always be two-pipe steam heat systems and the condensate return will always be take off of the bottom of the radiator.[14]

Certainly some of the two pipe steam heat radiators I have found in homes are bottom-fed steam radiators, have both entering and exiting pipes at the radiator bottom. It's hard to push steam "down".

The sketch at left shows that two-pipe radiator connections may be taken from either an upfeed or downfeed steam supply line - with just the information in the sketch we don't know which way steam is flowing in this system.

Holohan points out that because steam moves across the top of the radiator and condensate drips down along the sides of each radiator section, heat from a two pipe steam radiator system will be more "even" as the radiator is heating up.[1]

In our OPINION, once either radiator has become hot their heat output will be about the same regardless of one pipe vs two pipe design.

One Pipe Steam Radiator Piping Connections

At left is a one pipe steam heat radiator.

You can just make out the steam vent on the right side of the radiator, and at the radiator's lower left you can see the steam pipe and radiator valve - the steam enters and the condensate returns through the piping and valve at the radiator lower left end.

Down feed steam line and top steam valve on radiator (C) InspectApedia ITT

This is the most common one-pipe feed steam heat radiator piping we see in private homes.

An up-feed steam connection brings steam into the radiator through the Hoffman valve and that same valve allows condensate to return through the valve and into the steam line where it returns in the same steam pipe, flowing back to the steam boiler.

There are upfeed steam risers that flow steam into radiators at the radiator bottom in both one pipe and two pipe steam systems.

A one pipe steam system would not work if its steam entered at the radiator top - the radiator would fill up with condensate and would stop heating.

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. [14]

Dry Return Line Steam Piping

At left is a one pipe steam radiator connected with a dry return line.[14]

Indeed there is a wide range of both hydronic and steam radiators. A reasonable approach would be to

recognize that we have steam heat (look at the boiler, see steam vents or other steam controls at radiators)
recognize that we have hot water heat (the photo you cite offers that clue by its position on a cast iron radiator and also by the vent seen on the side of the valve itself). Keep in mind that some steam boiler systems may ALSO include hot water radiators on lower floors in the same building, often with a separate circulator pump.
recognize the type of radiator and thus follow its piping
older steam radiators of the type above will always have steam entering at the bottom and will have a steam vent on the opposite side of the radiator from that in which steam enters, and placed at or above the radiator's mid-height
distinguish between one pipe and two pipe steam systems for important reasons we can cite
some commercial or other newer steam radiators may have steam entering at the top of one end of the radiator. IN that case the construction of the radiator will be most likely serpentine - from the point of entry the steam may have to be pushed down one passage, then up the next to the far end of the radiator where there is a steam vent and a condensate return line, or probably more often, the radiator internals give a horizontal pathway. More often these will be convector units not conventional radiators. .

Vacuum / Vapor Steam Systems

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.

Frequently Asked Questions (FAQs) about types of steam radiator & steam radiator connections

...

Ask a Question or Search InspectApedia

Use the search box below to ask a question or to search the InspectApedia.com website.

Ask a Question or Enter Search Terms in the InspectApedia search box just below.

Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

[1] Dan Holihan, "Your Most Frequently Asked Questions About Cast-Iron Radiators – Answered! by Dan Holohan", http://www.oiltechtalk.com/pages/cast_iron.htm, retrieved 3/7/2013.
Barnes & Jones Corporation, 91 Pacella Park Drive Randolph, MA 02368, Tel: 781-963-8000calibrated steam traps and vents, Email: bnesbitt@barnesandjones.com. Vent-Rite steam vents for radiator control.
Energy Savers: Heat Distribution Systems, Steam Radiators & Hot Water Radiators, U.S. Department of Energy, web search 12/27/2010, original source: http://www.energysavers.gov/your_home
/space_heating_cooling/index.cfm/mytopic=12580
Gorton Heating Corporation, 546 South Avenue East, Cranford, New Jersey 07016, Tel: 908-276-1323, email: info@gorton-valves.com, fast venting valves for steam heating systems.
"Rv-4 One-Pipe Steam Radiator Valve", available from Armstrong International, 816 Maple Street, Three Rivers, MI 49093 USA, Tel: (269) 273-1415, Armstrong has offices in Beijing, China, Belgium, India and Mexico. Web search 12/27/2010, original source:
http://www.armstronginternational.com/thermostatic-valves-rv-4-one-pipe.
[6] "Special Steam Vents", Hoffman Specialty heating products, web search 12/27/2010, original source:
http://www.hoffmanspecialty.com/pdf/hs900/HS900-3474.pdf
[7] "Steam and Water Vents, Selection Guidelines - Steam Vents", Hoffman Specialty, web search 12/27/2010, original source:
http://www.hoffmanspecialty.com/pdf/hs900/HS900-stvents.pdf
Hoffman 1A adjustable steam vents, available from Hoffman Specialty, ITT, web search 12/27/2010, original source:
http://www.drillspot.com/products/51570/Hoffman_1A_Adjustable_Automatic_Air_Vent_For_Steam_Radiators
Hoffman Convector Steam Vents, available from Hoffman Specialty, ITT, web search 12/28/2010, original source:
http://www.hoffmanspecialty.com/pdf/hs900/HS900-conv109.pdf
[10] Report 95-14, PB96-198163 Thermostatic Radiator Valve (TRV) Demonstration Project, contact NYSERDA. 17 Columbia Circle, Albany, NY 12203-6399 Toll-Free: 1-866-NYSERDA, Tel:(518)465-6252, Ext. 241. Web Search 12/27/2010, original source: http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/96/960509.html
[11] VariValve® Quick-Vent from Heat Timer, adjustable radiator and main line vent valves for one pipe steam systems, web search 12/27/2010, original source: http://www.heat-timer.com/enFiles/ProductDocument/literature/VariV056082C.pdf
[12] "Care & Feeding of Air Vents", Dan Holohan, Old House Journal Online, November 2004
Steam Boiler Inspection, Diagnosis, Repair books at the InspectAPedia bookstore - Amazon.com
[14] 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
[15] Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
[16] The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
[17] 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).
[18] "Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
[19]The Heat Efficiency of Steam Boilers, Bryan Donkin
[20] Steam Boiler Operation, Principles & Practice, James J. Jackson
[21] Thanks to reader Paul Ruud for discussing improved steam heat controls and thermostatically operated steam radiator valves and air vents, 12/27/2010. Quoting:
"The modern version of this control is Johnson's V-3000-8012 (Exposed) and V-3000-8003 (Enclosed) Pneumatic Valve Actuators, Part No. 14-1078-32. Quoting from Johnson Controls, "The V-3000-8012 and V-3000-8003 Pneumatic Valve Actuators are designed to accurately position steam or water valve modulating plugs in response to a pneumatic signal from a controller. A V-9502 Valve Positioner can be ordered separately for use with the V-3000-8012 only, in applications where sequential operation is desired or additional positioning power is necessary. The actuators have a molded synthetic rubber diaphragm design. This molded diaphragm provides a constant effective area throughout the actuator stroke."
[22] Johnson Controls, "V-3000-8012 (Exposed) and V-3000-8003 (Enclosed) Pneumatic Valve Actuators Product/Technical Bulletin", Part No. 14-1078-22, 507 E. Michigan Street, Milwaukee, WI 53202, www.johnsoncontrols.com, retrieved 3/7/2013
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
  Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
  Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
  Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
  Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
...

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, 25th Ed., 2012, 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. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
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
...


	InspectAPedia^®	InspectAPedia
	Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair	Ask a Question or Search InspectAPedia

Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair

Ask a Question or Search InspectAPedia