Mark C. Honeywell's Patent for a New Type of Tee

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In a gravity hot water system, the hottest water is near the top of the horizontal main and tends to travel first to the upper-floor radiators. Mr. Honeywell, in 1909, patented this invention to help balance these systems. With Honeywell's tees in place, hot water would have to fill the entire pipe before any water would enter the radiators. The hot water had to slide under that internal cuff inside the tee to get to the radiators, so all the radiators heated at the same time. Beautifully simple!