Trane IntelliPak 3 with Symbio 800 Installation, Operation And Maintenance Manual page 20

Dimensional Data
Figure 8. Roof curb dimensions (inches)
F
RETURN OPENING
4.01
C
E
OPENING
B
A
TOP OF CURB
M
18.00
L 1.33
SUPPLY OPENING
K
OPENING
4.01
G
U
BOTTOM OF CURB
7.50
V
R
N
S
16.60
7.00
20 RT-SVX080A-EN