A direct-fired heater suitable for connection to duct work is provided. The heater comprises a combustion chamber defined by a combustion chamber wall, a burner plate at one end proximate a fan blade and an exhaust plate at an opposite end, the burner plate having openings therein for allowing airflow into the combustion chamber and the exhaust plate have an opening therein for allowing exit of heated exhaust from the combustion chamber, the combustion chamber wall extending past the burner plate. A first airflow zone exists between the outer shell and the combustion chamber allowing airflow between the fan blade and the outlet in the outer shell. An injector for injecting gas into the combustion chamber in proximity to the openings in the burner plate is used. The heater also comprises a nose cone between the outlet in the outer shell and the exhaust plate.