2025 marks a major milestone in the history of the Marlo Coil brand – our 100th anniversary!
The company was founded in 1925 by two brothers, Caesar and Angelo Marlo, in St. Louis, Missouri. The company began in the garage of the Marlo family home in the Italian “Hill” area of St. Louis, where the brothers started machining compressor parts for the Anheuser-Busch brewery.
They were soon joined by their cousin, Louis Pellegrini, who came to live with the Marlo family when his father died. In addition to making parts, the three young men began manufacturing fin and tube heat exchangers for local commercial and industrial customers. Caesar was talented in manufacturing, while Louis was a natural salesman. The two recognized the potential of the younger Angelo, and combined their incomes to put him through college. Angelo later became Marlo Coil Company’s first president.
The start of World War II presented a new opportunity for the company – to supply coils for U.S. naval vessels being deploying around the world. Marlo capitalized on this opportunity and grew the company significantly from 1941 to 1945, supplying heavy-duty coils for the U.S. Navy which not only offered reliable performance, but were built to survive the hazards of war.
During this time, Caesar (who was in charge of production) became notorious for walking the manufacturing lines several times each day. His constant statement to every employee was that he did not want his name connected with any product that was not the very best. That philosophy drove the company’s success during the war – and continues to drive Marlo’s success to this day, 100 years later.
The end of the war created the need for Marlo to develop more commercial products of all types, including central station air handling units, which we introduced in the mid-1940s. Around this time, another new challenge arose, and once again, Marlo Coil was there to deliver a solution.
With electrification spreading across the United States, hundreds of small towns built private electric power generating stations using diesel engine driven generators. The majority of these tiny plants were not on waterways, and the diesel engine oil systems needed to be cooled. Caesar developed a die to flatten round tubes and create excellent heat transfer coils for oil cooling. Marlo Coil dominated this market for years, filling the need for countless multi-hundred horsepower oil coolers.
In the early 1950s, Marlo opened new offices in Washington, D.C. and Upper Darby, Pennsylvania, and hired representatives in New York City, Pittsburgh, Baltimore and Roanoke. Growth continued in the coming years as the company expanded its commercial product line, as well as its military business, introducing marine grade air handling units around 1963 and Navy grade fan coil assemblies around 1965.
Unfortunately for the thriving business, Caesar Marlo died from a heart attack in 1967. Soon after, the Marlo family sold Marlo Coil to the H.K. Porter Holding Company. Then, in 1974, H.K. Porter decided to liquidate the company. However, Marlo still had many unshipped Navy orders at that time, so David Ault financed the purchase of the company assets from Porter —including all the dies, files and materials necessary to fill the Navy orders.
He rented vacant section of the Ford plant in St. Louis and continued to fill Navy orders under the name Nuclear Cooling, Inc. Two years later, in 1976, David Ault acquired the exclusive rights to the name Marlo Coil, and the company was officially reborn.
With the Navy business secured, the new Marlo was able to branch out into other military, commercial and industrial business opportunities, growing to the point where its rented space was no longer sufficient. So in 1980, the company built a new 185,000-square-foot manufacturing facility at the current Marlo headquarters site in High Ridge, Missouri (about 25 miles from downtown St. Louis).
Throughout 1980s and 1990s, Marlo outfitted hundreds of commercial and military vessels with heating and cooling coils, fan coils, air handling units and low temperature refrigeration units – focusing on U.S. Navy, Military Sealift Command and Coast Guard opportunities. During this same time, the company also continued to grow its commercial and industrial coil and AHU business and broadened its product line.
From 1998 to 2008, Marlo underwent a series of ownership changes. In 1998, Marlo Coil was acquired by Engineered Support Systems, Inc., which merged with DRS Technologies in 2006. DRS was acquired by Finmeccanica Company in 2008, which later became Leonardo DRS. As part of this restructuring, Marlo exited the air handling unit business and became the Marlo Heat Transfer Solutions product line of Leonardo DRS.
Marlo began significant reinvestment to grow the business in 2015. In 2018, the company re-entered the air handling unit business, introducing the MarloAIR AHU in response to customer needs for a quality, modular, pre-engineered AHU.
To support its continued growth, Marlo upgraded and modernized its manufacturing facilities between 2020 and 2025, adding multiple high-speed automated machines, including panel benders, hairpin benders, press brakes, laser cutters, robotic welders, and more. During this time, the company also greatly expanded its network of Independent Manufacturer’s Representatives for its commercial and industrial products, reaching full nationwide coverage.
Today, Marlo continues to serve both the commercial/industrial HVAC market, as well as the U.S. military. With a state-of-the-art facility, a highly skilled workforce, a local supply base, a commitment to continuous improvement, and a 100-year history of success, Marlo is well positioned to thrive as it enters its second century.
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