Page 10
Always introduce fresh makeup air so that it moves across the greatest dis-
tance within the room or building before reaching an exhauster.
Proper sizing of warm air ductwork is necessary to ensure a satisfactory heat-
ing installation. The recognized authority for such information is the Air Con-
ditioning Contractors Association, 1228 17th Street, N.W., Washington, DC
20036. A manual covering duct sizing in detail may be purchased directly
from them.
10. Electrical
Supply,
Connections,
and Controls
All electrical wiring and connections including electrical grounding must be in
accordance with the National Electric Code ANSI/NFPA No. 70 (latest edition)
or the Canadian Electrical Code Part 1-C.S.A. Standard C22.1. Check any
local ordinances or utility company requirements that apply.
Run a separate line voltage supply directly from the building electrical panel
to the disconnect switch for the system. All external wiring must be within
approved conduit and have a minimum temperature rise rating of 60°C. For
motor load amps, see Paragraph 12 or check the motor nameplate. System
FLA is on the rating plate.
Specific wiring diagrams and complete instructions are packed with each unit
and should be kept readily accessible in legible condition.
9. Distribution of
Makeup Air
(cont'd)
Sizing and
Installation of
Distribution
Ductwork
(See FIGURE 1, page 4,
for duct dimensions.)
Wire Gauge - 100 ft (30M) maximum
Full Load
Amps
5 10 15 20 25 30 35 40
Wire
Gauge
14 14 12 10 8
8
6
6
Disconnect Switch
A safety disconnect is required. Refer to FIGURE 8 for recommended loca-
tion and install the disconnect switch in accordance with Article 430 of the
National Electrical Code ANSI/NFPA 70 or in accordance with Canadian Elec-
o
The type of duct installation depends in part on the type of construction of
the roof (wood joist, steelbar joist, steel truss, pre-cast concrete, etc.) and
the ceiling (hung, flush, etc.).
o
Rectangular ducts should be constructed of not lighter than No. 26 U.S.
gauge galvanized iron or No. 24 B&S gauge aluminum.
o
All duct sections 24" or wider, and over 48" in length, should be cross-
broken on top and bottom and have seams or angle-iron braces. Joints
should be S and drive strip or locked.
o
Warm air ducts should not contact masonry walls. Insulate around all air
ducts through masonry walls with not less than 1/2" of insulation.
o
Insulate all exposed warm air ducts passing through an unheated space
with at least 1/2" thickness of insulation.
o
Duct Supports - Suspend all ducts securely from adjacent building
members. Do not support ducts from unit duct connections.
o
Duct Connections - At the heater, use a flexible canvas connection on
indoor units to eliminate vibration transmission.
On outdoor roof curb, down discharge connections, either drop an appro-
priate sized and flanged duct into the roof curb prior to setting the unit or
attach ductwork to the bottom flange (using curb dividers as ductwork). If
dropping ductwork from the top, it is recommended that the top perimeter
be sealed above and below the added ductwork. Do not use screws. See
ductwork connection locations and sizing, pages 7 and 9.
On outdoor horizontal installations, the ducts can be slid over the flange
of the heater and then sealed for an airtight and watertight fit. On horizon-
tal duct-to-heater connections and connections to the flanges at the
bottom of the curb, use sheetmetal screws to fasten ducts to the heater
flange. Use stiffening flanges around the perimeter of all duct connec-
tions.
o
Return Air Duct - The return air duct must be sized for a pressure drop
of .5" w.c. at 2440 fpm in order to balance the system. If not sized
properly, there may be difficulty in obtaining the desired airflow over the
burner when the return air damper is full open.
