It is required when installing the AquaStar 125FX model. The FX Hood will prevent cold air from freezing the heat exchanger on the AquaStar Tankless Water Heaters. A back draft preventer(FX Hood) should be used with all electronic ignition gas tankless water heaters where the outside temperature can fall below 32 degrees Fahrenheit. Also, the 125FX is classified as a category 3 by the national gas code so a vent hood is required. The 125FX has a built in power vent that pushes hot air out horizontally through a wall and needs to be vented through a vent terminator. The FXHood is designed specifically for the FX models that's why we recommend it. *Note: The FX Hood is NOT included with the purchase of an AquaStar 125FX.
** Exterior vent must not be any closer than local code allows - which in most cases is 4 feet from any opening to your home(ie windows, doors)and 1 foot above grade.

Bosch AquaStar FX Hood