Navien Inc. Navien condensing tankless water heaters & boilers for residential and light commercial applications use innovative high efficiency technology to provide a comfortable environment. NPE Series Application Drawings - Navien PDF fileNPE-A\S Series Tankless Water Heater. Note: Applications with a mixture of Navien NPE-A (Circulation) & NPE-S (Standard) the following should followed: 1. 50% of Tankless Units shall be NPE-A Models 2. Minimum of 2 NPE-A (2 of 3-4, 3 of 6) G H C. Gas Domestic Cold Water Condensate. G H C. Domestic Hot Water. Communication Cable G H C TANKLESS WATER HEATER INSTALLATION DIAGRAMS PDF filetankless water heater without taking the entire system offline. Piping or the plumbing manifold should be properly sized for the number of tankless water heaters being installed. See the Manifold Equipment Sched-ule, Form No. RTG11145, for details on pipe size and suggested equipment. Printed in U.S.A 01/09 Form No. RTG11142 Tankless Water Heater Genuine Navien Tankless Water Heater Replacement Parts With countless Navien water heaters in the field there is the evergrowing need to maintain the life expectancy of these units. While the life expectancy of a Navien tankless water heater is commonly 20 years or more, there can be component failure.