A fan powered box and a VAV (Variable Air Volume) box are two different types of air distribution systems used in HVAC systems. A fan powered box is a type of air distribution system that uses a fan to draw in outside air and then circulate it throughout the building. This type of system is usually used in larger buildings and is more efficient than a VAV system. The fan powered box also allows for more precise control of the air temperature and humidity levels.

A VAV box, on the other hand, is a type of air distribution system that uses a motorized damper to control the amount of air that is circulated throughout the building. This type of system is typically used in smaller buildings and is less efficient than a fan powered box. The VAV box also has less precise control of the air temperature and humidity levels.

Overall, the fan powered box is the more efficient and precise option for air distribution in larger buildings, while the VAV box is the more economical and less precise option for air distribution in smaller buildings.