November 06, 2008
Not Too Steamed
Regarding the article “Naturally Circulating Hot Water Systems” (Sept/Oct ’08, p. 6), I think Mr. Greenberg’s response is fine as far as it went, but there’s another possibility as to what this system might be. To recap: There is no circulator, and the supply pipes are larger than return pipes.
This might be a Vapor steam system. This type of system was the Cadillac of heating back in the day, and is still one of the best out there. Normally we find Vapor on high-end jobs, but I have seen Vapor systems in two-story row houses in the Baltimore area that were installed when the houses were built.
The typical Vapor system radiator or convector has a 3/4-inch supply connection and a 1/2-inch return. Most often there will be a thermostatic trap, water seal, or other device at the radiator return connection, but Vapor systems exist that did not have anything but a standard return elbow. The latter type is easy to misidentify as hot water.
Vapor system piping generally features a large steam main, at least 2 inches diameter, and two returns for each main that are smaller—one near ...
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