Steam Locomotive Feedwater Heaters: Elesco, Coffin & Worthington

Last revised: September 10, 2026

A feedwater heater takes exhaust steam that has already done work in the cylinders and uses it to warm water from the tender before that water enters the boiler. Cold feed is a tax. At typical working pressure the water already in the boiler is near 400°F. A live-steam injector will heat incoming water to around 200°F, but the remaining gap is thermal shock on the sheets and heat the fire has to make up. The heater puts that job on steam that would otherwise go up the stack.

Three makers owned the American market: Elesco (the Superheater Company), Coffin, and Worthington. Closed heaters (Elesco and Coffin) kept exhaust steam and feedwater apart. Open heaters (Worthington) mixed them and skimmed the oil. By the 1930s a heater was standard on new mainline power, and Worthington’s SA type was the one most roads specified. Not every locomotive received one. Fuel was sometimes cheaper than the pumps, piping, and leaks.

This page is that appliance—how it works, the three common types, and how to read one on a smokebox. How a boiler makes steam is on the steam locomotives hub. The injector and the superheater can be found at the glossary. Finally, the firebox can be found here.

Chesapeake and Ohio 2-8-2 1214 Class K-3 switching coal hoppers at Ronceverte West Virginia October 22 1952

Chesapeake & Ohio 2-8-2 No. 1214 (Class K-3) switches coal hoppers at Ronceverte, West Virginia, October 22, 1952. Alco built the fifty K-3s in 1924 (1210–1259) with Elesco K-40 heaters. C&O retired the class as it dieselized in 1952–53. None survive.

On this page: At a glance · Why preheat · Open and closed · Elesco · Coffin · Worthington · How to identify them · Why not every engine

At a glance

Item	Detail
What	An appliance that preheats tender water with cylinder exhaust steam before the water enters the boiler
Job	Fuel saving and less thermal shock. Typical service claims were on the order of 10–15 percent less coal than an injector-fed engine doing the same work
Heat source	Exhaust steam after the cylinders, not live boiler steam
Closed type	Elesco (Superheater Company) and Coffin (J.S. Coffin Jr. Company). Feedwater in tubes; steam outside; condensate back to the tender
Open type	Worthington (Worthington Pump and Machinery). Exhaust steam mixes with the feed; oil is skimmed
U.S. commercial start	A working heater on a large Pacific in 1916. About 4,100 in service on this continent by 1927
When they became standard	On new mainline power by the 1930s. Worthington SA the most common late-steam specification
What they usually replaced	The live-steam injector on the fireman’s side. The engineer’s injector typically stayed as a backup
Related appliances	The superheater (dries steam on the way to the cylinders). The injector (forces water into the boiler). Exhaust-steam injectors (heat recovery without a heater pump set)

Why the water had to be warm

A steam locomotive is a boiler on wheels. Water from the tender keeps the crownsheet covered as steam is made and used. That tender water sits at whatever the weather is doing. The boiler, at 200 to 250 psi on a typical late engine, holds water near the saturation temperature—roughly 388°F at 200 psi, about 406°F at 250. Shoving cold water into that drum cools the sheets, costs steam, and makes the fire work twice: once to reheat the feed, once to make the steam the cylinders actually want.

A live-steam injector already does some of the heating. It mixes boiler steam with the incoming water to force that water in against boiler pressure, and the mix arrives around 200°F. The remaining 200-degree gap is still a drain. The energy in that injector steam came from the fire. A feedwater heater uses exhaust that has already pushed the pistons. The fire does not pay twice.

Makers and road tests in the 1920s typically claimed on the order of 10 to 15 percent less fuel than an injector-fed locomotive on the same work. The Superheater Company advertised 12 to 15 percent for Elesco. Closed-heater tests were reported in a band from about 9 to 16.5 percent. The heater also let a boiler make steam faster when the engine was working hard, and it spared the firebox and barrel some of the shock of a cold slug. Lima treated a high-efficiency feedwater heater as part of the Super Power kit, with the larger grate and a Type E superheater; that story is on the firebox page and the steam hub.

Open heaters and closed heaters

Every American locomotive heater of the late steam era did the same thing with two different plumbing diagrams.

In a closed heater the feedwater runs through small tubes inside a steam-filled shell. Exhaust steam never touches the water that will go into the boiler. Condensate from that steam is collected and piped back to the tender, so the water is not thrown away. Elesco and Coffin were this type. The price was copper tube nests that leaked, and a pump (or pumps) to shove the water through the nest and then into the boiler against pressure.

In an open heater the exhaust steam mixes directly with the incoming water. Heat transfer is simple and the apparatus can be compact. The open type needs two pumps: a cold-water pump to lift from the tender into the mixing chamber, and a hot-water pump to force the heated feed past the boiler check. Worthington built this type. The obvious objection was cylinder oil in the exhaust. Worthington answered it with a separator and a continuous skim of the scum that floated on the mixing-chamber surface. By the last generation of new steam, roads that had once preferred closed heaters were specifying Worthington.

On the engine the heater usually took the fireman’s injector. The engineer kept a live-steam injector as a backup and for standing. That is why a heater-equipped locomotive still has injector piping on one side and a pump, a heater body, and a nest of pipes on the other.

A cheaper cousin, the exhaust-steam injector, also recovered some heat from the stack steam. The Superheater Company sold an Elesco exhaust-steam injector as well as closed heaters; Sellers made another. It is not a feedwater heater. It has no mixing tank or tube nest. It is an injector that can run on exhaust when the engine is working and switch to live steam when it is not. Some roads used it instead of a heater to keep the first cost and the maintenance down. The glossary entry for injectors is here.

Elesco

Elesco is a spoken abbreviation. The Superheater Company—organized in 1910 as the Locomotive Superheater Company to put Wilhelm Schmidt’s smoke-tube superheater into American service—lettered its feedwater gear LSCo. Say the letters: El-Es-Co. Instruction books from the 1920s carry the New York and Chicago addresses and the Elesco name on closed heaters, pumps, and, separately, exhaust-steam injectors.

The heater that made the brand visible is the bundle: a horizontal cylinder of copper tubes, four passes in the mature design, mounted on the smokebox ahead of the stack or partly dropped into the top of the smokebox. That drum is the “beetle brow” on so many 1920s photographs. Water from a pump on the fireman’s side of the boiler ran through the tubes; exhaust steam filled the shell; condensate drained back to the tender by gravity. Early pumps were a single-cylinder reciprocating machine that looked like a Westinghouse 9½-inch air compressor. Later applications used a duplex pump or a centrifugal.

A later Elesco coil heater put a less bulky exchanger ahead of the stack instead of the big drum. The plumbing idea did not change. By the late 1920s the company was advertising more than 2,200 Elesco heaters on American-built locomotives, against more than 52,000 of its superheaters. The superheater was the company’s original product. The heater was the add-on that used the same exhaust the superheater had already helped make more useful in the cylinders.

Chesapeake & Ohio specified the Elesco K-40 on the 1924 K-3 Mikados, including 1214 in the hero photograph. Rio Grande specified Elesco on the simple 2-8-8-2s of classes L-131 and L-132. The bundle on 3615 at Sierra is that heater.

Denver and Rio Grande Western 2-8-8-2 3615 Class L-132 with Elesco bundle feedwater heater at Sierra Colorado 1950

Rio Grande 2-8-8-2 No. 3615 (Class L-132) in a curve at Sierra, Colorado, 1950. The horizontal cylinder on the smokebox is an Elesco bundle-type feedwater heater. Robert LeMassena photo. American-Rails.com collection.

Alco-Schenectady finished the ten L-132s (3610–3619) in June 1930. They were simple articulateds, not compounds, with a Type E superheater layout and an Elesco heater as built. 3615 was one of three in the class that later carried three thermic syphons in the firebox. The class encyclopedia is the Rio Grande 2-8-8-2 page; the company is Denver & Rio Grande Western.

Coffin

The J.S. Coffin Jr. Company brought a closed heater of a different shape about 1927. The exchanger is a horseshoe or inverted U, rectangular in cross-section, with five tube passes, bent to the curve of the smokebox. As designed it sat inside the top of the smokebox, flush with the wrapper, so the engine kept a clean face. A turbine-driven centrifugal pump under the cab, on the fireman’s side ahead of the trailing truck, shoved water through the nest. Condensate went back to a small auxiliary heater in the tank, which warmed the tender water before it reached the pump.

When the same heater was hung on the front of an existing smokebox it became one of the most argued-over looks in steam. Railfans call the external Coffin a cobra hood or a heavy eyebrow: a dark arch over the top half of the smokebox door. Boston & Maine’s Lima 2-8-4s of 1928–29 (class T-1) wore that face as built. New York Central, which cared how a Hudson looked, put Coffin gear inside the smokebox on some passenger engines instead of hanging it out front. Fewer roads standardized on Coffin than on Elesco or Worthington. The heater worked. The plumbing and the face were the arguments.

Worthington

Worthington Pump and Machinery Corporation of Harrison, New Jersey, sold the open type. The first widely applied locomotive model, later called the BL, appeared around 1920. Pump and heater were one large rectangular casting, usually on the fireman’s side of the boiler. From the platform it is easy to read as a second air compressor. It is not. The cold-water pump lifts from the tender; the mixing chamber is in the same box; the hot-water pump sends the heated feed to the boiler checks.

The type that won the late steam era was the SA (and the related S / S-2 family from about 1929). The heater itself is a tank inset into the top of the smokebox, ahead of the stack—a box rather than Elesco’s cylinder. The pumps are separate: cold water under the cab, hot water often on the pilot deck. Piping is cleaner than the BL. Oil still entered with the exhaust, and the SA still skimmed it. Roads that had fought the open type on contamination grounds came around once the separator proved out in shop reports.

By the 1930s, when a new 4-8-4, 2-10-4, or simple articulated left the builder, a Worthington SA was the default specification more often than not. C&O’s later Texas types wore it. So did a long list of Super Power freight engines. The BL never disappeared from older power, and some roads mixed makers across a class as engines were shopped.

How to identify them

Look at the smokebox first, then the fireman’s side.

What you see	What it is
Horizontal cylinder on or partly in the smokebox, ahead of the stack	Elesco bundle (closed). The common 1920s face
Smaller coil exchanger ahead of the stack, no big drum	Later Elesco coil (closed)
Deep or unusually tall smokebox, no drum, no eyebrow	Often a Coffin (closed) inside the smokebox
Horseshoe or arch over the smokebox door (“cobra hood,” “heavy eyebrow”)	Coffin (closed) hung on the front, typical of retrofits and of Boston & Maine Berkshires
Large rectangular box on the fireman’s side of the boiler, not an air pump	Worthington BL (open). Combined pump and heater
Rectangular tank inset in the smokebox top; separate pumps under the cab and on the pilot	Worthington SA (open). The late-steam standard

Air pumps sit on the smokebox front or the side as well, and they confuse the Worthington BL more than any other heater. Count the piping. A BL has tender suction, a delivery to the boiler check, and exhaust-steam connections into the same casting. An air compressor has reservoir piping and no tender hose.

Why not every locomotive had one

The thermodynamic case was never the whole case. A heater added first cost (on the order of $2,500 a set in 1920s figures), extra pumps, extra copper, extra joints, and a shop skill that not every roundhouse had. Closed-heater tubes leaked. Open heaters needed the oil skim kept honest. On a coal-cheap district, or on a switcher that spent its life drifting and standing, the injector was enough. Branch engines and older power often kept both injectors and never received a heater. New mainline freight and passenger power after about 1930 usually did.

That is why a 1924 C&O K-3 and a 1930 Rio Grande L-132 both wear heaters in the photographs on this page, and why a 1910 ten-wheeler on a short line often does not. The appliance belonged to the era that was already squeezing every pound of steam out of a Super Power boiler. Dieselization ended the argument. The heaters went to the scrapper with the engines.

Sources

Barris, Wes. “Steam Locomotive Feedwater Heaters.” SteamLocomotive.com appliance page (open vs closed; Elesco name; identification of bundle, Coffin, Worthington BL and SA)
Railway and Locomotive Engineering, August 1927. Feedwater-heater paper: 1916 U.S. Pacific application; about 4,100 heaters in service on this continent; Elesco, Coffin, and Worthington described; first-cost figure about $2,500
The Superheater Company. Elesco Locomotive Feed Water Heaters instruction books (1925; 5th ed., 1929). Elesco as LSCo / Superheater Company product
Superheater Company advertising, Transportation, 1927–28. Elesco claimed 12–15 percent less fuel per thousand ton-miles; more than 2,200 Elesco heaters and 52,000 Elesco superheaters applied
International Correspondence Schools. Locomotive feedwater heating equipment. Elesco closed system about 1920; Coffin about 1927; Worthington open type, BL around 1920, SA the late standard
Locomotive Cyclopedia (1947). Worthington S / SA / S-2 family from 1929
Llanso, Steve. Locobase 482 (C&O K-3 / K-3a, Elesco K-40 on the K-3s, Alco 1924, dieselization 1952) and Locobase 16242 (D&RGW L-132, Alco-Schenectady June 1930, works 68328–68337)
Shuster, Philip, Eugene Huddleston, and Alvin Staufer. C&O Power. Alvin Staufer, 1965. K-2 / K-3 as C&O gradient mainstay
Solomon, Brian. The Majesty of Big Steam. Super Power practice (larger firebox, superheater, feedwater heater as a kit)

Facebook X Pinterest Tumblr Reddit WhatsApp Messenger