Sales Model of a Lennox Furnace – ca 1920

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This model was made ca 1920 by the Lennox Furnace Company of Marshalltown, Iowa. The model is made of aluminum and was used by the Warm Air Heating Research Laboratory of the University of Illinois. Similar models were used by salesman for marketing purposes. The model represents the Lennox’s Torrid Zone domestic furnace number 50-27, which is stamped on the fire door. This furnace type is shown in a 1929 Lennox catalog and offered for sale at $112.00. It was intended for domestic heating installations. The Torrid Zone line of furnaces was introduced by Lennox around 1895, and the line evolved and continued to be sold well into the 20th Century. The furnaces were made of riveted steel construction versus cast iron which was then standard. The advantage of the steel construction was improved durability and reduced risk of cracking which could result in combustion gases leaking into the heated air from the furnace. Another design improvement was a sectional fire-pit liner which could be made of cast iron or firebrick. The sectional design enabled the liner to be removed and replaced through the fire door without disassembly of the entire furnace. Lennox also introduced the “Diving-Flue” as a part of the radiator at the rear of the furnace. This structure caused the combustion gases from the furnace to first pass downwards along the surface of the radiator closest to the furnace and then upwards at the rear of the radiator and thence through the flue to the chimney. This exposed the maximum surface area of the radiator to the hot gases and improved the efficiency of the furnace. The entire Torrid Zone furnace was intended to be enclosed within another structure which circulated air over it to be heated and carried via convection to rooms above the furnace room. In later production, the Torrid Zone furnaces were used in installations using fans for forced air heat distribution to the rooms.
The model is shown in the image. It is highly detailed and clearly illustrates the important elements of the furnace’s design and function including all of the access doors, humidifier, sectional fire-pit, radiator and “diving-flue”, and the lever for shaking the ashes into the ash-pit.
Currently not on view
date made
ca 1920
associated place
United States: New York, Syracuse
United States: Iowa, Marshalltown
overall: 10 5/8 in x 7 3/4 in x 11 3/4 in; 26.9875 cm x 19.685 cm x 29.845 cm
ID Number
catalog number
accession number
Credit Line
Gift of National Warm Air Heating & Air Conditioning Association. Cleveland, Ohio
Sales model
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Work and Industry: Mechanical and Civil Engineering
Engineering, Building, and Architecture
Data Source
National Museum of American History


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