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Belt tension vs air flow

metrosilo Member Posts: 33
I’m not an HVAC tech so be kind. Gas fitter. I was setting up combustion on an air make up and my temp rise on low was too high. I’m wondering if there is not enough air flow across exchanger. The belts were quite loose on the supply air motor. Does that affect how much air the fan is moving?
Or is it only if the belts slip, the fan performance drops. 


  • Jamie Hall
    Jamie Hall Member Posts: 23,567
    If the belts are slipping, your performance will go way down (the fan may almost stop completely!). There should be a spec. for belt tension; too little is very bad, but too much is also not good, as it loads the bearings too much.

    If there is no spec. available, a deflection of somewhere around a quarter inch per foot of distance between pulleys with one hand pushing on the belt might be a place to start.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • pecmsg
    pecmsg Member Posts: 4,916
    The motor amperage will tell you how hard the motor is working. Overtightening will not increase speed but WILL destroy bearings!
    To change the speed, change the sheaves. Drive motors come with adjustable sheeves. They need to be set up on day one to the proper RPM and air flow for that piece of equipment (open or closed to reach that #). Then the adjustable is removed and fixed sheeve installed.
    EBEBRATT-Ed Member Posts: 15,767
    belt deflection should be the thickness of the belt at mid span with moderate finger pressure
  • leonz
    leonz Member Posts: 1,168
    edited October 2022
    If you are working on V belts you need to purchase a V belt tension gauge
    you can buy the DAYCO V belt tension gauge 93865 from a NAPA store.

    If the V belt is glazed, cracked or the rubber dust comes off the belt and in
    your hands the V belt is shot.