Reply by DIYaholic

I’m no mechanical engineer, but you should/may be able to put a smaller pulley on the motor & a larger pulley on the fan. This would decrease the fan RPMs, hence reduce air flow. Greater minds may be able to help, when they chime in.

I’m using a repurposed squirrel cage furnace blower for my air cleaner also. However my fan is a direct drive, variable speed (variac??, think router speed control), unit so no pulleys.

Good luck.

-- Randy-- I may not be good...but I am slow!