I have 1" lines running my full loop from boiler and back. About 90' underground and about the same in the house. It feeds DHW, hot tub tube HX, one air to water HX, then off to another water to air HX in that order. My inside line runs the full length of my rancher from end to end. I have a 10 plate HX for my HW and have 2 showers, 2 dishwashers, and 2 clothes washers tied in. I have never had a problem with having enough hot water, but very rarely is every appliance using it at once. My hot water lines from my hot water tank are also 3/4" and adapted to the 1" or 1-1/4" ( I forget) ports on the HX.