Worn fan belts can decrease air delivery by as much as 20%.
This spring as you prep hot weather ventilation fans by cleaning blades and shutters, greasing bearings and removing winter covers, one of the essential items on your checklist should be the V-belts.
Fans belts don’t stretch, they wear. Belts become thinner as their sides rub against the fan pulleys. As they get thinner the belts ride lower in the pulley grooves causing the fan blades to rotate slower. The slower the blade rotates, the less air it moves. It is not uncommon for slippage caused by worn fan belts to decrease air delivery by as much as 20%. Cubic feet per minute delivery is directly proportional to the fan speed. Spin a fan 20% slower, and it moves 20% less air.
Think of what this reduction means in a house with 12 fans rated at 324,000 cfm with a designed airspeed of 600 feet per minute. Worn belts could reduce cfm by 20% or down to 259,200 cfm. This turn would lower the airspeed to only 480 feet per minute; severely decreasing the amount of wind chill felt by the animals or birds during hot weather.
Plan to replace fan belts every year. Keep in mind although automatic belt tensioners reduce the amount of slippage causing the belts to wear slower, they do not eliminate the need for annual replacement. Same for link style belts; the biggest benefit of link belts is how easy it is to have the right size belt on hand. Link belts still wear over time and should be replaced annually just like conventional belts.
The second item in the fan drive system requiring attention is the pulleys themselves. Over time pulleys also wear, changing from a V shape to a rounded profile. This wear is easily checked when installing a new belt. If the new belt does not ride high on the pulley but instead slips down into the pulley groove, then it is time to replace the pulley. Pulleys typically need replacing about every four years.
One of the best tools available when changing or even just checking pulley alignment is a product called the Laser Fan Pulley Alignment Kit. This inexpensive device uses a laser pointer to ensure fan pulleys are in perfect alignment. It’s easy to use, just place the laser pointer in one of the pulley grooves and adjust the pulley on the shaft until it matches up. Not only can the kit be used when installing new pulleys, but also when changing fan belts to be sure the pulleys have not shifted over time.