Igor Zhadanovsky, FacilitiesNet
April 21, 2017
Summary
Near the end of the 19th century, an unknown engineer stood up before a trade association meeting and said, “It is possible that in a few years from now we will be heating … by steam below atmospheric pressure, of such a low temperature that it gives all of the advantages of hot water without any of its disadvantages.” That statement, quoted in “Practical Steam and Hot Water Heating” by A.G. King, may once again be true today.
Vacuum systems were considered to be the Cadillac of steam heating systems (SHS) in the 1900s because of their efficiency and comfort: Back then, conversion from steam to vacuum system saved an average of 35 percent in fuel costs, according to Dan Holohan, “The Lost Art of Steam Heating,” 19th edition. An elegant method was used to overcome the innate problem of uneven heat distribution: instead of pushing air from SHS with 1-2 psig steam, a 6-10 inches mercury vacuum (roughly 3-5 psi pressure drop) is employed in a closed system to pull vapor into radiators quickly, evenly, and at lower temperatures. Vapor in a vacuum travels at impressive speeds — up to 160 miles per hour. An additional bonus is the elimination of air vents, air hissing, and hot water spitting.
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