
OM0298
September/2020
Page 15 of 102
5.2.7 Exhaust Duct Installation Guidelines
The exhaust system must provide conditions similar to that under which the cabinet was certified to meet its
stated performance. The following guidelines should be observed when installing exhaust air ductwork for either
existing plant exhaust systems or a new exhaust system.
1. Adequate room make-up air inflow to replace exhausted air. Air diffusion rate is not to exceed velocity of
100 LFPM (.51 m/s) to minimize disruptive air currents. If laboratory is to be pressurized, follow
guidelines in ANSI/AIHA Z9.5 Laboratory Ventilation.
Room Make-Up Air Requirements (CFM/CMH)
Utilizing Concurrent Balance Values
2. Plant should have adequate exhaust system capability.
The exhaust system is usually adequate if it can provide the rated exhaust flow and static pressure.
3. All duct losses must be considered and added to the cabinet loss in selecting the exhaust blower, for a
new exhaust system (i.e. duct diameter, length and number of elbows, etc.).
4. All ductwork should be securely anchored to the building construction in manner to be free from vibration
and swaying under all conditions of operations.
5. Sheet metal gauges and seams should be in accordance with the current edition of the ASHRAE guide.
A minimum of 20 gauge for round duct is required to prevent duct collapse due to high static pressure
conditions (square duct will require heavier gauge material).
6. All ductwork should be maintained at a negative pressure within the building (i.e. externally located
exhaust blower).
7. The exhaust blower and duct work should be a sealed system that can hold 2.0 inches(51mm) w.g.
pressure for 30 minutes with no more than a 10% drop in pressure, and be properly vented to the
atmosphere to disperse exhausted air.
8. A local manual exhaust flow damper (Nuaire Model NU-940) should be readily accessible (either directly
mounted on the BSC exhaust collar or just above the BSC) for the maintenance technician/certifier to
allow the BSC to be sealed for decontamination purposes.
If a Constant Air Volume (CAV) valve is located above the BSC, any exhaust flow adjustments should be
made to the CAV valve leaving the manual exhaust damper in a full open position.
9. It is recommended that the cabinet operation be interlocked with the exhaust blower.
Fan relaycontacts are provided for this purpose.
However, it is also recommended to have a manual exhaust override switch near the cabinet for
certification and service.
For multi-ganged systems, this switch could be used to interface with a Building Automated System (BAS).
10. It is recommended that when using the NU-951-012 automatic butterfly valve, the system air volume
must remain within ten percent of the given nominal setpoint volume. Variations greater than ten
percent will result in incorrect air volume measurements on the BSCC airflow control system.
11. It is not recommended to hard connect (i.e. weld) the exhaust connection to the cabinet.
This may damage the exhaust filter and/or the butterfly valve (if present).
A silicon sleeve (Nuaire Part No. NU-940-001), banded between the cabinet's exhaust duct and the plant
exhaust duct is recommended, with no more than a two-inch gap between the ducts, for a 1/8 inch
(3mm) thick silicone sleeve.
If Nuaire damper valves are present, see Drawing BCD-05572 for installation.
12. If duct diameter reduction is required, it is recommended that the reduction occurs at least
12 inches (305mm) from the cabinet duct connection and that the reduction is smooth and gradual to
reduce air turbulence that results in noise and loss of static pressure.
13. IT IS NOT RECOMMENDED TO CONNECT THE CABINET DUCT CONNECTION DIRECTLY INTO A 90-DEGREE
BEND. The cabinet's exhaust airflow sensor could be affected by airflow turbulence created by 90-degree
bends. If a 90-degree bend is required, it is recommended that the 90-Degree bend occur at least
12 inches (305mm) from the BSC exhaust collar.