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The Hartford Loop used on steam heating systems, definition, functions, inspection, installation, repair:
This article gives a definition of the Hartford Loop used on steam heating systems, explains why the Hartford Loop is necessary to protect against steam boiler damage, and gives a bit of the history of the development of the Hartford loop.
We include sketches and photographs of the Hartford Loop piping arrangement on steam boilers and list inspection & defect points of interest.
Hartford Loop safety piping arrangement on steam boilers
Definition of the Hartford Loop - what is a Hartford Loop & Why is it Important on Steam Systems?
Invented in the U.S. in 1919 by the Hartford Steam Boiler and Inspection Company in response to an unacceptable rate of steam boiler damage, loss, and even explosions, the Hartford Loop is a piping arrangement at the steam boiler condensate return line that allows condensate to re-enter the boiler but prevents complete loss of steam boiler water should a leak develop elsewhere in the condensate return line.
Today the company refers to itself as the Hartford Steam Boiler Inspection and Insurance Company (founded in 1866) - not to be confused with the Hartford Fire Insurance Company (founded in 1810).
[Click to enlarge any image]
As you can infer by looking at our drawing at above left Boiler Without a Hartford Loop, a leak anywhere in the wet return portion of the condensate return piping that is below the boiler water line risks siphoning out all of the water from the heating boiler.
Our illustration at above right titled Hartford Loop shows where the Hartford Loop is located on a steam boiler. Above the drawing is adapted from ITT's The Steam Book.
The 2-inch Rule and the 24-inch Rule for Hartford Loops & Steam Headers
In steam piping layout the top of the Hartford Loop will be located at a height that places it 2" below the water line in the steam boiler.
Check out our blurry photo at left. That yellow arrow points to what should be a 2-inch dimension. Toes that look like 2" to you? This Hartford Loop may be improperly piped, risking failure to keep a safe level of water in the boiler should a leak occur in the wet condensate return piping.
The connection of the right-hand Wet Return portion of the Hartford Loop to the first piping loop closest to the boiler is made using a close nipple. If the short horizontal run (green arrow in our sketch) is made too long the anti-siphon benefit of the Hartford Loop could be lost.
But the boiler manufacturer may provide additional steam piping specifications - as we illustrate below. For example instead of specifying that the top of the Hartford Loop is two inches below the boiler water line the manufacturer may specify that the pipe fitters maintain at least 24 inches between the boiler water line and the bottom of the steam header.
The risk of steam condensate return water leaks was and can remain significant because of the corrosive acids that form in steam and other heating boilers and because not coincidentally, the more likely place where such leaks would develop is in the last and lowest run of the condensate return line along or close to the floor approaching the steam boiler.
In our discussion of steam condensate systems we illustrate a chemical injection system intended to reduce this corrosivity.
At below right our image is adapted from the piping schematic for a Weil McLain steam boiler - Weil McLain Model 78 (2014)
Boiler manufacturers typically specify that a Hartford Loop piping arrangement and a wet condensate return line are required for steam boilers.
In addition to the installation of Hartford Loop to prevent total boiler water loss from a leak in the condensate piping, [the wet condensate return line] a steam boiler specification will maintain at least 24 inches from the steam boiler water line (see GAUGES, STEAM BOILER) to the bottom of the steam header.
And if a separate condensate receiver is used, a feed pump to move condensate back to the boiler must be energized by a boiler-mounted condensate return pump controller. (see CONDENSATE RETURN PIPES, PUMPS, STEAM) - adapted from Weil McLain 78 boiler instructions.
A separate worry for Hartford-loopless steam boilers has been suggesteed by Steam Boiler Gurur Dan Holohan - paraphrasing
The Hartford loop is needed to prevent steam pressure in the condensate return line from forcing the liquid condensate (water) out of the boiler and back into the return piping system - something that could be a serious problem resulting in boiler water loss and boiler damage or destruction.
The “wet” gravity return line, which returns the condensate from the system, rises up from the floor to join with the equalizer at a point about 2 in. below the boiler’s lowest operating waterline.
[Steam boiler installers ...] didn’t always use this piping arrangement. They used to bring the return directly back into the bottom of the boiler without the benefit of either a Hartford Loop or an equalizer. When they piped a boiler this way, however, the slightest steam pressure would push water out of the boiler and into the return. [Emphasis ours - Ed.]
They solved this problem by using a check valve in the wet return (that’s the pipe below the boiler waterline).
Before long, though, they found the check valve would fill with sediment and get stuck open.
That caused the water to back out of the boiler again, so they developed the equalizer pipe to replace the check valve. ...- Dan Holohan,PM Mag, online, un-dated, retrieved 4/7/2017 cited at REFERENCES
Dan continues to point out that leaks at the return line were catastrophic for steam boilers and adds that the low water cutoff valve (LWCO) was not invented until E.N. McDonnell invented it in 1923.
Really? The pressure in a residential steam heating system is normally less than 0.5 psi. At WATER PRESSURE MEASUREMENT (not specifically a heating system article) we describe how to compute the pressure exerted by water at the bottom of any vertical column of water - say a condensate return pipe, for example.
Even without a Hartford loop, and assuming for argument that the steam boiler is in a building basement and that the normal or "safe" water level in the boiler itself is at most 4 ft. above the floor, we can calculate that
The pressure of a column of water is about 0.433 psi per foot of column height.
The pressure of a 4 ft. height of water in the steam boiler and also in the riser of the condensate return pipe wherever it mounts to upper floors, measured at the bottom of that column of water, will be
Water pressure in the steam system at floor level (WPfl) = 4 x 0.433 psi = 1.732 psi.
If my calculations are right (I'm not a boiler engineer) we have about 1.7 psi of resistance to water leaving the steam boiler and 0.5 psi or less of steam pressure trying to push water out of the boiler.
So I think that for low-pressure residential steam systems the greater risk is not steam pressure pushing much water out of the boiler, but rather a leak anywhere in that close-to-floor-level condensate return line. (However the risk of boiler water push-out at high pressure steam boilers would be another and still more serious matter entirely. )
Leaks Do Occur in the Condensate Return Line
Do leaks actually occur in the wet return portion of a steam heat condensate return piping system? You bet they do. Depending on what's done to manage steam boiler chemistry, the condensate may be quite corrosive. Our photo at left shows two leaks at the condensate wet return at a boiler located in in the U.S. in Poughkeepsie, NY.
History of the Hartford Loop & the Hartford Steam Boiler & Insurance Company
Comment: the Hartford Steam Boiler & Inspection Company
2017/04/07 Nancy said:
Quick correction. The loop was invented by the The Hartford Steam Boiler Insurance and Inspection Company (Where I work - we're 150 years old!). The Hartford Insurance co. is a different entity all together.
Nice job with a basic, easy to understand explanation!
Reply: The Hartford Steam Boiler Inspection and Insurance Company is not the Hartford Fire Insurance Company
Thanks for the clarification, Nancy. Indeed it's easy to be confused about Hartford Insurance and Hartford Fire Insurance companies. The Hartford Insurance and Hartford Boiler company were of a piece.
In sum it would be fair to say that the Hartford Loop was invented by and a key feature of
The Hartford Steam Boiler Inspection and Insurance Company founded on June 30, 1866.
While the Hartford FIRE Insurance company was and remains a different company.
Munich RE, parent company of the HSB group, publishing as the Hartford Steam Boiler Inspection and Insurance Company at www.munichre.com/HSB/hsb-history/index.html says
The Hartford Steam Boiler Inspection and Insurance Company was founded on June 30, 1866. Our first president considered HSB as “the first company in America devoted primarily to industrial safety.” “Hartford Standards” quickly became the specifications for boiler design, manufacture and maintenance.
Insurance incentive for boiler inspection
The Polytechnic Club spent much time debating about an idea that combined insurance with a boiler inspection. They reasoned that inspections would increase boiler safety and the insurance would function as an incentive to inspect and a guarantee of a quality inspection.
Though the insurance offered financial interests, it was secondary to safety and loss prevention – a totally new concept for an insurance offering.
Under that premise, The Hartford Steam Boiler Inspection and Insurance Company was founded in 1866.
Separately at the Hartford Insurance Comany's website www.thehartford.com/about-us/hartford-history one sees that the company was founded as the Hartford Fire Insurance Company.
The Hartford was founded in 1810 in Hartford, Connecticut. A group of local merchants gathered in a Hartford inn and, with working capital of $15,000, founded the Hartford Fire Insurance Company. ...
In 1810, we started as a fire insurance company, employing our own fire department to protect customers. Fifteen years later, we wrote the first insurance policy for an institution of higher learning – Yale University.
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Questions & answers about the Hartford Loop on steam boilers
Question: is a missing Hartford Loop a problem on a steam boiler system?
(Aug 31, 2016) Ei said: A recent inspection revealed no Hartford Loop on the boiler (replaced burner 2014). Is this a problem and what is the cost to install one.
We replied in detail where you posted this question elsewhere.
(Oct 3, 2016) Anonymous said:
there is a question if a blowdown on the loop is needed since it is the lowest point of the boiler?
No. Not that I've seen nor read about.
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Weil McLain Model 78 Boiler Manual, Boiler for gas, light oil, Gas/Light Oil fired BUrners, Installation, Start-up, Parts, Maintenance instructions, Part No. 550-141-705/0600, Weil-McLain Administrative Office, 999 McClintock Drive, Suite 200, Burr Ridge, IL 60527
Tel: 855-248-1777 Consumer Inquiries: 800-368-2492 Technical Services: 800-526-6636 Technical Support for Contractors Only.
If you are a homeowner and are experiencing a problem with your Weil-McLain equipment, the first step you must take is to contact your installer or locate an HVAC contractor in your area. Website: http://www.weil-mclain.com
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.
Holohan, Dan, "Top 10 facts about the Hartford Loop" [web article], Radiant & Hydronics, Plumbing & Mechanical Magazine,
2401 W. Big Beaver Rd., Suite 700
Phone: 248-362-3700, website: pmmag.com, retrieved 2017/04/07, original source: http://www.pmmag.com/articles/96529-top-10-facts-about-the-harford-loop
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
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.)
McDonnell & Miller Controls - XYLEM Global Headquarters,
1133 Westchester Avenue,
White Plains, NY 10604,
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