We received a call today about this so here’s some quick thoughts (as in NOT EXHAUSTIVE) for roof or wall exhaust fan belt replacement:

  1. Identify belt length and type
    1. Measure center to center on pulleys (aka sheaves)
    2. Measure outside diameter of each pulley
    3. Measure the width of pulley gap where belt enters
    4. Typically the belts are V type, with either an A or B width
      1. If low HP type fans, usually A
      2. If high HP, usually B
    5. Count number of grooves (usually one or two) – this tells you how many belts are needed
  2. Buy the belts LOL (if you want the best set it and forget it solution, click here to give us some details and we’ll quote you what we use)
  3. Put the new belts on starting on the smallest pulley and rolling on to larger
  4. Check tension by twisting the belt at the center point – proper tension is typically a half turn at the center distance between pulleys (this is not technically spot on but tends to be very close and avoids needing a belt tension measuring device in a pinch – for less critical equipment like this it works fine)
  5. If tension is too tight or too loose, adjust at the motor mount (should have a way to adjust distance) NOTE: if you use our belt solution above you won’t need to do this!
  6. Re-check belt tension after the fan has run for a few weeks as the belts tend to stretch during break-in. NOTE: if you use our belt solution above you won’t need to do this!

Things to avoid:

  1. Disconnect and lockout the power before you touch anything!
  2. Belt over-tightening – leads to premature bearing and belt failure
  3. Belt under-tightening – leads to loss of power transfer along with a premature belt and pulley failure
  4. Pulley/Sheave misalignment – check 3 planes with a straight edge/string/laser