A furnace is disclosed. The furnace may include an enclosure having a vertical support column formed by a heat exchanger compartment panel and a blower compartment panel. The furnace may include a window assembly having venting openings hidden by a viewing window. The furnace may also include a rail to support a removable heat exchanger system. The furnace may further include a wire retaining fin assembly to retain a wire. A heat exchanger header design including features to retain a sealant is also disclosed.