Hartford loop piping schematic for a steam boiler - adapted from ITT's The Steam Book - (C) InspectApedia Daniel FriedmanThe Hartford Loop on Steam Boilers
Definition, function, safety features, piping for the Hartford Loop

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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.

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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?

Hartford loop piping schematic for a steam boiler - adapted from ITT's The Steam Book - (C) InspectApedia Daniel Friedman Hartford loop piping schematic for a steam boiler - adapted from ITT's The Steam Book - (C) InspectApedia Daniel Friedman

Invented in the U.S. in 1919 by the Hartford (CT) Insurance 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.

[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

Steam boiler hartford loop improperly piped (C) Daniel Friedman

  • 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)

Steam condensate return leaks (C) D Friedman Hartford loop piping schematic (C) InspectApedia

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, 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.

Leak in steam heat condensate return line at the boiler (C) Daniel FriedmanDo 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.

Watch out: at CONDENSATE RETURN PIPES, PUMPS, STEAM we explain that a leaky condensate line such as the one shown in our photo at above left can be lead to dangerous BLEVE EXPLOSIONS.

You can check the water level in your steam boiler quite easily by using the built-in STEAM BOILER SIGHT GLASS.

The Hartford Loop is also discussed at STEAM HEAT DEFECTS LIST





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