Navien NPE-2 series units replace inefficient tank heaters, saving water, natural gas and electricity with added benefits of endless supply of hot water, lower maintenance costs and longer product life. Cascade up to 32 units in side by side or back to back configurations with the NPE-2 series.The Ready-Link Manifold System provides everything an installer needs for a side-by-side wall-mounted application, side-by-side floor-mounted rack application or floor-mounted back-to-back applications.