Navien NFC series is available in 175,000 Btu/h and 199,900 Btu/h models, each offering 95% AFUE, 11:1 turndown ratio, PVC venting up to 150’, and residential and commercial warranties. The Navien NFC combi-boiler models come with a patented in-house designed and manufactured heat exchanger, advanced controls offering intuitive user navigation, a built-in DHW module with mixing valve, water adjustment valve and auto water fill valve, cascading and common venting capability, built-in hardware for 3-zone pumps without a need for external controllers and 16 included accessories featuring a NaviClean magnetic filter and NFC primary loop manifold, the company says. Navien.