The Bosch® 8738725270 is an outdoor air intake filter designed to protect the combustion air fan on Bosch Greentherm gas tankless water heaters. Its pleated paper media captures dust, pollen, insects, and other airborne debris before it reaches the combustion chamber, reducing the risk of burner blockage and premature failure. The filter installs on the appliance's air fan inlet and is recommended for units in dusty, high-pollen, or high-particulate outdoor environments. HVAC and plumbing service professionals install and periodically replace the filter to maintain clean combustion airflow after confirming the appliance model and intake configuration.