The Thermal Valve Model, Type F, of the Ruud Instantaneous Automatic Water Heater is a design that allows the user to instantaneously heat water for on demand applications while not heating, thus saving fuel, when not in use. The Type F was able to use LP gas, natural gas, and gasoline, requiring only a change of burner spud orifices, and was manufactured in two variations, the "Standard Pressure Heaters," designed to operate in conditions where pressure was at least twenty-five pounds per square inch (1.7 bar), and "Low Pressure Heaters," where operational water pressure could be as low as four pounds per square inch (0.3 bar). Thermal Valve Model, Type F heaters were manufactured in four residential sizes reflective of their output in gallons per minute: 3, 4, 6, 8.[10] In 1915, there were approximately one-hundred-thousand of the Type F installed throughout The United States and Canada.[10]
The water heater arm of Ruud Manufacturing was purchased by Rheem in 1959.[4] However, the Ruud name continued with RUUD Heating and Air Conditioning Equipment