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Confused about "pumping away" and Knight WH installation
First, "Hi." First time poster. I'm trying to understand and apply the principal of pumping away from the PONPC, but a figure in the Lochinvar Knight WH installation manual has me confused. (If the figure doesn't attach, it's Figure 6-10, page 45 in the WH installation manual). The figure shows piping for "full flow" (i.e. not primary/secondary) with a DHW priority loop. The confusion I have is that both the Boiler (=System) and DHW circulators are pumping into the boiler, which then feeds directly into the expansion tank. Since the boiler has such low head loss (0.5 ft/hd @ 7 gpm for the WHN-055), doesn't that break the "pumping away" rule?
Wouldn't it make more sense to move the expansion tank and the two circulators, so the flow would go from boiler --> expansion tank --> tee --> one circulator on each leg of the tee? That way both pumps are immediately after the expansion tank. I asked Lochinvar tech support but they said that the installation manual shows the configuration that's been "tested for years" and that the boiler needs to be pumped into to ensure flow (i.e. preventing overheating).
What do you guys think? Is the manual right, or not? And if not, do I risk voiding the warranty if I install it against Lochinvar's recommendations?