Matching Boiler:HotWater with a WaterHeater:Mixed

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I am attempting to model a WaterHeater:Mixed the same as a Boiler:HotWater.

I know that the Boiler:HotWater uses a performance curve, while the WaterHeater:Mixed has a static efficiency. What efficiency value in the WaterHeater:Mixed closely match the Boiler:HotWater?

Does the Boiler:HotWater assume a particular source water temperature from district or is district water not used at all when there is no domestic hot water use?