The internal fans maintain acceptable operating temperatures for the internal components by drawing in cool
air through the vents and circulating that air through the chassis.
The direction of airflow is from front-to-back.
To ensure adequate airflow through the equipment rack, we recommend that you always maintain a minimum
clearance distance as mentioned in the following specifications.
• Front clearance—5 inches (12.7 centimeters)
• Rear clearance—3.93 inches (10 centimeters)
Note the following points:
• When installing chassis in a back-to-back position with another device, ensure a minimum of 3.93 inches
(10 centimeters) airflow clearance between them. Also, ensure that the device behind the chassis is not
installed in a way that it blows air into the chassis.
• An over-temperature condition may occur within the rack, if airflow through the rack and the device is
restricted, or if the air that is drawn into the rack is warm.
• Ensure that the site is dust free. Dust tends to clog the device fans, reducing the flow of cooling air
through the equipment rack and the devices that occupy it, thus increasing the risk of an over-temperature
condition.
• Enclosed racks must have adequate ventilation. Because each device generates heat, ensure that the racks
are not congested. An enclosed rack must have louvered sides and a fan to provide cool air. Heat that is
generated by the equipment near the bottom of the rack may be drawn upward into the intake ports of
the equipment above.
• When mounting a chassis on an open rack, ensure that the rack frame does not block the exhaust fans.
• When a rack-installed equipment fails, especially equipment on an enclosed rack, if possible try operating
the equipment by itself. Power off all other equipment on the rack (and in adjacent racks) to give the
device maximum cooling air and clean power.
• Avoid installing the chassis in a location in which the chassis air intake vents may draw in the exhaust
air from an adjacent equipment. Consider how the air flows through the device; the airflow direction is
from front to back, with ambient air drawn in from the vents located on the sides of the chassis.
When mounting the device on any type of rack equipment, ensure that the temperature of inlet air to the device
does not exceed the specified operating temperature limits of the product.
Caution
Airflow Guidelines for Site Planning
Maximum System Airflow (CFM) at
Maximum System Temperature
Feature
Device
105
12 x 1/10GE SFP, AC Model
ASR-920-12SZ-A
12 x 1/10GE SFP, DC Model
ASR-920-12SZ-D
Cisco ASR-920-12SZ-A and Cisco ASR-920-12SZ-D Aggregation Services Router Hardware Installation Guide
19
Prepare for Installation
Airflow Guidelines for Site Planning
