Sizing Guide

22 Sizing Guide www.hartandcooley.com
A. COMBUSTION AIR requirements MUST be supplied
from outside the living areas from sources such as
hallways, service areas or outdoor balconies in
accordance with the information in NFPA Standard
54 ANSI Z223.1. It is preferred that this air be taken
into the appliance room directly from outdoors. This
is important because any restriction in the common
vent or termination will cause flue products of all
appliances below this obstruction to spill out the
draft hoods of other appliances just below this
obstruction.
B. Other Cautions
1. Provide proper clearance to combustibles around
the common vent in its chase or shaft.
2. Use the highest connector rise possible. If
capacity is borderline, use the next size connector.
3. The only draft effect to be considered available is
due to the vertical height from the draft-hood
relief opening of the highest appliance on that
floor to the point where the connector for the floor
above enters the common vent. NEVER USE THE
HEIGHT TO THE TERMINATION except for the
top floor.
4. The appliance on the first floor is considered to be
self-venting (vertical height 5 feet or more), and
therefore sizing is calculated using Table 2 Single-
Appliance Venting.
Type B Double-Wall Gas Vents
Table 7
Min.
Input Available Total Common
Total BTUH Connector Vent Connector Vent
Appliance To Common Vent Rise Height Size Size
1 90,000 10' 10' 5" self-venting connector
2 180,000 1' 10' 6" 7"
3 270,000 1' 16' 6" 7"
4 90,000 6' 6' 5"
self-venting connector
Special Considerations and Additional Precautions