1. Blowers should be mounted on the roof in-order that the  ducting  leading to the blower inlet is under negative static  pressure. If exhaust blowers are mounted inside the  building, all ducting connected to the blower outlet will be  under positive static pressure, if a leak were to develop in  the section of the duct inside the building, toxic and or  hazardous fumes could be forced out of the ductwork and  into that area of the building.

2. To achieve the lowest practical noise level in the exhaust  system, we suggest that the following measurements be  used when there is no conflict with other specifications of  the system:

a. Use vibration isolators or mounting blower exhaust  assembly.

b. Install a blower fan that will deliver the correct CFM and  static pressure with the lowest practical impeller wheel  RPM. If possible, use a duct size large enough to keep duct  velocity under 1800 FPM velocity.

c. Use a flexible connection at the fan inlet to isolate  mechanical transmission of noise from the ducting  between the hood and the exhaust blower.

d. Exhaust blower system should be designed with the fewest  possible elbows or other fittings. Use radius type elbows &  avoid using square elbows. Use gradual tapered transitions  where necessary, & avoid abrupt changes in configuration or  cross sectional area.

3. When ordering an exhaust blower, specify the orientation of  discharge desired. Vertical up blast discharge is the most  common and will be supplied unless otherwise specified.

4. All fans are shipped with clockwise rotation when viewed  from the motor end of the assembly.

5. For normal usage, the standard for both the blower housing  and impeller wheel is epoxy coated.

6. Blowers used for hood exhaust at altitudes above 1,000 feet,  may require a correction factor to provide the correct CFM and  static  pressure.

Contact factory for details relating to your specific application.

1. It is recommended that exhaust blowers be located at the
 end of the ducting which is typically roof mounted. This
 ensures a negative pressure through out the ventilation    system. However for applications where the duct is going  directly out through a wall above a fume hood, one option is  to have a fiberglass direct drive blower installed in the top of  the fume hood. By having the blower internally mounted, the  installation is simplified and convenient for duct connection  and servicing. However there would be an airflow sound  element associated to having the blower hood mounted.

2. By keeping the exhaust duct as short and as straight as  possible, the total resistance will be reduced and by keeping  the diameter of the duct correctly sized to the flow volume,  noise and static pressure can be reduced.

3. Blower wheels for polypropylene and fiberglass blowers
 are polypropylene.

4. Vibration isolators are recommended when mounting the
  blower assemblies

5. HEMCO recommends that a sash stop be installed on the
 fume hood to limit the sash height for operation. By having
  stop at a half open position, the total CFM can be reduced by  50%; thus by reducing the volume, energy loss, duct
 diameter, motor and blower size, and sound is reduced.

• CFM at 100 fpm face velocity

• Housing is constructed of heavy gauged galvanized steel, with a
  baked enamel finish, to resist weather & chemical exposures.

• Flange inlet collars enable easy connection to ductwork.

• Wheel is dynamically balanced to minimize noise and increase
   efficiency.

• Ball bearing pillow blocks are per-lubricated and resistant to both
   moisture and dirt.

• Shaft is constructed of polished steel with a coating to prevent rust
  and corrosion.

• Motors meet NEMA standards for single speed motors.

• These blowers are ideally suited for both supply and exhaust
   applications in  laboratories, educational, pharmaceutical,
   industrial, and other applications.