A belt tensioning system for a motor and a belt-driven blower each secured inside an air handling unit. The blower rotatably carries a first shaft, a first sheave and a bladed arrangement being secured to the first shaft. A second sheave secured to a second shaft is rotatably carried by the motor. A belt engaging the periphery of the first sheave and the second sheave urges the first sheave to rotate about the first shaft in response to the motor urging the second sheave to rotate about the second shaft. An adjuster having adjustment means is secured to the structure. Actuating the adjustment means in a direction urges the motor either toward the adjuster or away from the adjuster to vary the distance between the first sheave and the second sheave to vary the tension in the belt.