The Suburban P-40 has the same cabinet size as the NT Series, but is equipped with a long-life, heavy-duty AC motors and controls. The P-40 is designed for use in recreational park trailers. The P-40 features: Gasket-sealed vent assembly Energy-saving solid state electronic ignition Steel gas manifold Sealed forced-draft combustion Stainless Steel vent cap Wall thermostat Duct Outlet Size: Sides 4" round, Bottom 10" x 3-1/4" Duct Outlet Size: Sides 4" round, Bottom 10" x 3-1/4"