A burner assembly including a housing and an airflow restrictor plate for selectively restricting an amount of airflow passing out of the housing in order to reduce a heat output of the burner assembly. The housing has an air inlet and an air outlet and is configured to guide an airflow from the air inlet and out of the housing via the air outlet. The airflow restrictor plate has a single opening through which all airflow flowing through the housing from the air inlet must pass in order to exit the housing via the air outlet.