I am planning to convert to a tankless water heater but have a few questions to make sure I am on the correct path.
I live in a rowhouse in Philadelphia where natural gas is used for heat and my water heater tank is located in the basement by the front of the house where the water (and gas) enter the house. I want to relocate the new tankless water heater to more central location that is closer to the points of demand. I am planning the placement to on the wall about a foot away from the stack and below the kitchen. I want to avoid cutting through the exterior wall for the venting and was hoping I can run the piping along side the stack (not sure about the spacing requirements) inside the interior wall that separates the kitchen and dining room on the first floor and bathroom and bedroom on the second floor and vent through the roof.
The questions I have are: 1) it is copper piping throughout and was thinking to replace the 3/4" feeding with PEX but maybe it would be helping to keep copper to help the water warm up a bit before reaching the heater. Is it better to keep it copper since PEX is a better insulator. 2) Not sure whether to use concentric or not, would be great to only cut one hole, but maybe I want to add some exhausting venting from the bathroom upstairs which means I might need add a separate exhaust pipe anyway. If do not go with the concentric can I use the exhaust piping to vent the bathroom exhaust too? is there a backstop.
Any information would be appreciated.