Venting for a Navien Tankless Combination Unit

miketumminello

Looking for some help with venting for two combi units in the same house. I have a NCB-180 combination unit and a NCB-240. I have the exhaust set up outside already but the intake is set up on the inside. Instead of drilling 2 more holes into the wall for the other unit, i was hoping to keep only the 2 holes drilled through the wall for the vent and somehow vent the other unit through the 2 holes. If i have to drill the other 2 holes for the intake/exhaust then I will but before doing so i want to make sure there is not another way to vent the 2 units. The smaller unit is about 10-15ft away from the wall where the larger unit is about only 5ft away.
If anyone has an idea on the best way to vent these units whether it be with Zvent stainless or CPVC, please share. Thank you.

Rich_49

Use a concentric kit . Extend the exhausts out about an additional foot to lessen chances of make up sucking in the exhaust fumes . 2 Holes , 2 intakes , 2 exhausts , DONE

Use whatever PVC you'd like for the intake air and PolyPropylene for the exhausts