Hi. I purchased a Vevor inline fan to ventilate my custom sauna. The fan is 120vac, 1.14 amp 0.17 hp. It includes a variable speed control integrated into the power cord. The problem is that the lowest speed setting is too much air flow for my application. The max speed is 750 CFM, not sure what CFM the lowest speed is but that will rapidly empty my 6' X 9' sauna of heater air in no time. I'd rather not just buy a smaller fan because the exhaust duct (and fan) are 8". My objective is to control the fan speed from 0 to it's max. I've called around, one source said use a potentiometer, another said use a TRIAC controller.

I'm handy enough to eliminate the controller that is integrated into the power cord and connect and use only a new device. But what new device should I use?

 

Some depends on the type of motor shaded pole, or cap run motor.
Can you open the control and see what technology is in the present one?

 

A TRIAC type lamp dimmer controller would likely work but it can cause buzzing of the motor.
I have slowed down a floor-fan motor silently using non-polarized film capacitors in series with the motor.
You would need to experiment with the value of the capacitor to get the desired speed.
You can buy a few 1µF, 250V caps and connect them in parallel until you get the desired speed (example vendor).
I would expect you won't need more than about 8µF total.

 

that will rapidly empty my 6' X 9' sauna of heater air in no time.

Surely the whole point of having a fan is to remove moist air quickly and efficiently? Moisture remaining leads to the spread of fungi/mould. Can't you just have your sauna, then let the fan do its job quickly and then switch it off?
Btw, Crutschow's suggestion does work, but you have to be careful that the capacitance and fan motor inductance don't form a circuit which resonates at the mains frequency or a harmonic, as that can result in very high damaging voltages.

 

Surely the whole point of having a fan is to remove moist air quickly and efficiently? Moisture remaining leads to the spread of fungi/mould. Can't you just have your sauna, then let the fan do its job quickly and then switch it off?
Btw, Crutschow's suggestion does work, but you have to be careful that the capacitance and fan motor inductance don't form a circuit which resonates at the mains frequency or a harmonic, as that can result in very high damaging voltages.

This is a Finnish sauna. The purpose of the fan is twofold. First to slowly draw fresh air in during the sauna session (provide oxygen, eliminate CO2 buildup) and secondly to evacuate moist air after the session.

 

Some depends on the type of motor shaded pole, or cap run motor.
Can you open the control and see what technology is in the present one?

The 0.17hp motor has a cbb61 8.0uf run capacitor in an enclosure next to the motor. It also has a on/off 3 speed 'control' integrated into the power cord which I can easily eliminate if needed to accomplish my objective (i.e. to control the fan from 0 to its max CFM). There are not markings on the 3 speed control. I attached a picture. Thanks

 

If you use a capacitor to reduce the motor speed, you could use a SPDT switch to bypass the motor controller, and connect the capacitor in series when needed.

 

"........ the fan speed from 0 to it's max. " is not achievable with the type of motor you have. The speed of these motors is locked to the main's frequency (50Hz -60Hz) and the number of poles inside, which in the case of fans, it is almost always 2 pole to get max speed. The only proper way to control the speed of this motor is decreasing the AC frequency which is not the way you would want to go.
Alec_t gave you the best advice and cautions. One last resort, if want to have steam sauna but the fan is too powerful, is to make your own contraption and adjust the air flow by partial blocking the air flow, but you need to make sure if your fan pushes the same 750 cubic foot per minute because it is cooling itself as well. the contraption would be something like when you block the vent partially , it opens another pathway for the ventilator to get air flow from other environment other than your sauna. a crude sketch is like this , so when you narrow the air flow from sauna, the trap door widens another path for the air to flow thru motor to compensate air flow restriction :

 

"........ the fan speed from 0 to it's max. " is not achievable with the type of motor you have. The speed of these motors is locked to the main's frequency (50Hz -60Hz) and the number of poles inside, which in the case of fans, it is almost always 2 pole to get max speed.

The fact it has a cap indicates it could be a PSC motor where both windings are identical , these are common fan motors, cieling fans etc and are commonly RPM controlled via a Triac fan controller on the wall plate., I have several around my home.

 

The purpose of the fan is twofold. First to slowly draw fresh air in during the sauna session (provide oxygen, eliminate CO2 buildup) and secondly to evacuate moist air after the session.

For safety's sake it would be inadvisable to slow the fan below the sauna manufacturer's low speed limit during the sauna session. Build-up of the combustion products would be a major health hazard.