This is because of the fact that the amount of friction is greatly reduced in case of this fan when the fan is operating.
Direct drive vs belt drive attic fan.
Direct drive fans require fewer parts and thus usually less maintenance.
That would be quiet but would look like a mess from outdoors.
Where on a belt drive fan the fan motor shaft has a pulley connected by a belt to a second pulley.
Greater efficiency is the biggest pro of direct drive fan configurations.
When compared to belt drive fans which require belts sheaves and bushings direct drive is just plain simpler and maintenance folks tend to lean toward direct drive for daily maintenance.
That pulls more air with less fan noise.
Unlike the belt driven fans in case of a direct drive fan there is lesser energy loss.
Direct drive fans have no power transmission loss since the propeller is directly connected to the motor shaft.
Both types are available as direct drive with the fan blade attached to the motor and belt drive with.
Belt drive whole house fans that use an integrated pulley system take longer to install but a belt drive unit provides for a smoother and quieter operation.
Belt drive fans are quieter than direct but still noisy.
However a belt drive fan has power transmission loss due to the friction between the belt and sheaves and due to the drive shaft bearings.
Most whole house fans are relatively easy to install.
Unlike belt driven fans there s less energy loss because there s a reduced amount of friction as the fan operates.
In a direct drive configuration the fan motor that controls the movement of the fan blades is connected either to a shaft or fan axle.
I had a belt drive with a two speed motor years ago.
For pricing and availability.
Spruce spruce rb series ventilation fans 8 in steel single direct drive whole house fan.
Attic fan prices expect to pay between 50 to 400 and up for an attic fan depending on the type and quality.
The second pulley is connected to a shaft that drives the fan propeller.
I think that the belt drive blades can turn slower with a deeper pitch than a direct drive.
I fantasized building a small shack outside my house and setting the attic fan in the shack and running a duct up to the attic and through the same vent as an attic fan.
Thus the fan blades will rotate at the same speed as the motor rotates.
Belt drive attic fans are usually much quieter than direct drive models though the latter are often cheaper.
Sizing a whole house fan.
You have a fan a motor and maybe a coupling.
Direct drive models are the most do it yourself friendly because for most no attic joists need to be cut.