12
RP-HRPD-IOM (07-22) 132210-B
INSTALLATION—CONTINUED
Duct Connections—Continued
Ductwork Requirements
• Type:
the type of duct installation to be used depends in part on the construction type of the roof (wood joist, steel
bar joist, steel truss, or pre-cast concrete) and ceiling (hung, flush, etc .) .
• Material:
rectangular duct should be constructed of not lighter than #26 US gauge galvanized iron or #24 B&S
gauge aluminum .
• Size:
proper sizing of supply air ductwork is necessary to ensure a satisfactory heating installation . The recognized
authority for such information is the Air Conditioning Contractors Association, 2800 Shirlington Road, Suite 300,
Arlington, VA 22206 (
) . A manual covering duct sizing in detail may be purchased directly from them .
• Structure:
all duct sections 24 inches (610 mm) or wider and over 48 inches (1,219 mm) in length should be
cross-broken on top and bottom and should have standing seams or angle-iron braces .
• Joints:
should be S and drive strip or locked .
• Ductwork through masonry walls:
no warm air duct should come in contact with masonry walls . Insulate around
all air ducts through masonry walls with not less than 1/2 inch (1 inch is recommended) of insulation .
• Ductwork through unheated space:
insulate all exposed warm air ducts passing through an unheated space
with at least 1/2 inch (1 inch is recommended) of insulation .
• Supports:
suspend all ducts securely from buildings members . Do not support ducts from unit duct connections .
• Access panels:
Install removable access panels (see
) on both the upstream and downstream sides of
the furnace . The access panels must be accessible when the furnace is in service and should be a minimum of
6
×
10 inches (152
×
254 mm) in size so smoke or reflected light may be observed inside the casing to indicate
the presence of leaks in the heat exchanger . Ensure that the access panels are installed in such a manner so as
to prevent leakage .
• Horizontal discharge duct length:
A minimum horizontal duct run of 24 inches (610 mm) is recommended before
turns or branches are made in the duct system to reduce losses at the furnace outlet .
• Supply air duct/furnace horizontal connection:
The seal between the furnace and the duct must be mechanical
using U-type flanges on the top and bottom of the connecting duct to to ensure tight joints and an airtight fit . Refer
and perform the following steps:
a . Ensure that flanges on the furnace (heat exchanger) turn out as shown .
b . Shape duct connection as shown: U-type on top and bottom and L-type on sides .
c . Slide U-channels over furnace top and bottom flanges making connection .
d . Form U-channels to seal sides (see DETAIL A) and drill and lock with sheet metal screws .
• Connection dimensions:
connection dimensions (inches (mm)) are shown in
DETAIL A
Figure 7. Connecting Ductwork to Furnace
