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With this Electric Boiler setup, would this be considered PONPC and pumping away? With the confined space this layout would provide the tidiest look and least amount of piping, fittings, supports, etc. Seems to me like it would be proper enough. I figured the AS on the supply tapping at the warmer water would be most appropriate. There would also be ball valve and drain tap on the return side upstream of the make-up/fill. That would provide fast purging all entire system through the boiler.