National Oilheat Research Alliance 19 from the primary loop. The tees that connect the secondary circuit should be no more than 12″, or 4 pipe diameters – whichever is less, apart. If the secondary circuit is piped in ¾", the tees should be 3" apart. Because the water temperature drops as it circulates through the primary loop, it’s important to connect the secondary circuits that require the hottest water (baseboard) at the beginning of the primary loop and those that require lower temperatures (radiant) towards the end. When there is a call for heat, both the primary and secondary circulators operate and the secondary circulator pulls water from, and returns it to, the primary loop. Figure 8 Figure 9
NORA Advanced Hydronics
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