Dan Holohan discusses one of Mark Honeywell’s contributions to gravity hot water heating. He wanted to create even heat throughout the building, so in 1909 he solved the problem of stratification on the long, horizontal runs of pipe by inventing this unusual fitting. The water inside the horizontal main has to be hot all the way to the bottom before it can slip under that metal wall and flow up to the radiator. This meant that all the radiators along a horizontal main would get hot water at about the same time, which helped balance the system. Wonderfully simple!
Want to learn more? Read Dan Holohan’s book Classic Hydronics: How to Get the Most From Those Older Hot-Water Heating Systems.