Navien NCB-250/150H Recirculation

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Hello, I'm getting ready to install this combi boiler but I have a few questions about recirculation on the DHW side. 3 techs from navien gave me 3 different answers so im hoping someone here can clarify. I want to ensure that I have hot water available as quickly as possible at all of the taps. With that being said I have a 2100 sq ft house built in 1999 without a dedicated return line and with a 50' maximum distance of piping between the DHW and the furthest faucets. What would be the best and quickest way to get hot water? I would like to mention that with the 40 gallon water heater i have now it takes about 30-45 seconds to get hot water at the shower so i guess if i can get water in the same amount of time or less that would be acceptable also. As far as setup goes should I use the combi pre heat function with internal recirculation or should I get a navicirc or similiar thermal bypass valve in combination with a external circulator pump and set the unit to External recirculation. Maybe theres another method that might work best for my situation? Any input is greatly appreciated.
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