A direct-drive exhaust fan has the blades mounted straight on the motor, so there is no belt to adjust or replace. A pulley-driven (belt-driven) drop hammer fan uses a 1440 RPM motor and a belt to turn the blades, and is the traditional design. Both move the same air in each size; the difference is maintenance and power options.
What a drop hammer fan is
A drop hammer exhaust fan is a box fan with a shutter on the outlet. A small weighted arm (the "hammer") opens the shutter when the fan runs and lets it fall shut when it stops, keeping out rain, dust and birds. It is the standard exhaust fan for factories, poultry houses and greenhouses.
How the two drives differ
| Direct drive | Belt and pulley | |
|---|---|---|
| How it turns | Blades on the motor shaft | Motor turns blades through a belt |
| Fan speed | 460 to 560 RPM (by size) | Motor at 1440 RPM, reduced by pulleys |
| Maintenance | No belt; minimal | Belt tension checks and belt replacement |
| Power supply | As specified for the model | Single or three phase |
| Motor | 0.37, 0.55 or 1.1 kW by size | 1440 RPM motor |
| Airflow per size | Same as belt drive | Same as direct drive |
Airflow by size (both drives)
| Size | Airflow |
|---|---|
| 800 mm (32 inch) | 18,000 m³/h |
| 1000 mm (40 inch) | 23,000 m³/h |
| 1380 mm (54 inch) | 44,000 m³/h |
All our drop hammer fans are made in India with six SS-304 blades and a 1.2 mm body.
Choose direct drive when
- You want the least maintenance: no belts to check, slip or replace
- Fans are hard to reach, such as high on factory walls
- Many fans run long hours, as in poultry tunnel ventilation
Choose belt drive when
- You want the familiar design that local electricians and mechanics know well
- You need a specific power supply option, single or three phase
- Spare belts and pulleys are easy to get on your site
Maintenance tips for both
- Clean blades and shutters regularly; dust and feathers reduce airflow
- Check the shutter opens fully and closes freely
- On belt fans, check tension and wear every few weeks in peak season
- Make sure there is enough inlet air: fans cannot pull air out of a sealed room
See all exhaust fans or the poultry fans page.
Frequently asked questions
What is a drop hammer exhaust fan?
A box exhaust fan with a shutter that a weighted arm opens when the fan runs and closes when it stops, keeping out rain, dust and birds.
Is a direct-drive exhaust fan better than a belt-driven one?
Direct drive needs less maintenance because there is no belt. Both move the same air in each size.
Are your exhaust fans made in India?
Yes, with SS-304 blades and a 1.2 mm body.