I'll try to be brief. Older house, long run to upstairs bathroom. Recent installation of a Navien propane fired combo unit. Water is nice and hot once it gets there, but takes more than a minute and the same to the kitchen. Old furnace was oil-fired and was in line with an Amtrol WH-7 Boiler Mate hot water maker. Right now the old furnace and the Amtrol are still in the basement, nonfunctional. Would there be any advantage to keeping the Boiler Mate hooked up in conjunction with the Navien? Could I put an undersink circulator in the upstairs bathroom to keep a loop going between bathroom and Amtrol without affecting the sensing of the Navien? I am the homeowner and my understanding of HVAC is very limited, so please speak slowly. Thanks in advance for any help.