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I'm just about to start a job to replace a boiler in a 3,000  Eichler home; all on a single thermostat. The distribution piping is 3/8" copper tubing and because of the high pressure drop, I plan to use a Grundfos 26-99 circulator, piped directly, i.e. no primary-secondary configuration. In addition, there's an on-board circulator on the IBC HC boiler, so there will be two circulators in series, increasing the head pressure.
- 1" supply and return
- Two manifolds, both with butterfly valves on the 3/8" tubing. Some of the valves have been turned off. All the valves are frozen.
- The interior is all original. Minimal insulation and single-glazed windows.
- The previous boiler and circulator were gone by the time I got there, so I have no idea what was used before.
I plan to put pressure gauges on the suction and discharge sides of the circulator to find the duty point of the system.
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