16
B. All Air From Outdoors:
When air is supplied directly from outside the building, each opening shall have a minimum net free area
as noted:
COMBUSTION AND VENTILATION AIR (Indoor Units Only)
The heater must have both combustion and ventilation air. Minimum requirements for net free air supply open-
ings are one opening that is 12 inches from the ceiling for ventilation, and one opening that is 12 inches from the
floor for combustion air as outlined in the latest edition of the National Fuel Gas Code, ANSI Z223.1(Canada-
CAN/CSA-B149) and any local codes that may have jurisdiction.
CAUTION: Combustion air must not be contaminated by corrosive chemical fumes which can damage the
heater and void the warranty.
A. All Air From Inside The Building:
Each opening shall have a minimum net free area as noted:
Model Square Inches
259 250
400 399
Model
Unrestricted Opening (sq. in.)
Typical Screened or
Louvered Opening (sq. in.)
Typical Screened and
Louvered Opening (sq. in.)
259 63 95 126
409 100 150 200
Direct Vent and Ducted Combustion Air Systems
If outside air is drawn through the intake pipe directly to the unit for combustion:
1. Install combustion air direct vent in accordance on page 21 (horizontal) or page 22 (vertical) of this manual.
2. Provide adequate ventilation of the space occupied by the heater(s) by an opening(s) for ventilation air at
the highest practical point communicating with the outdoors.
a) In the US, the total cross-sectional area shall be at least 1 in.
2
of free area per 20,000 BTUH (111 mm
2
per kW) of total input rating of all equipment in the room when the opening is communicating directly
with the outdoors or through vertical duct(s). The total cross-sectional area shall be at least 1 in.
2
of free
area per 10,000 BTUH (222 mm
2
per kW) of total input rating of all equipment in the room when the
opening is communicating with the outdoors through horizontal duct(s).
b) In Canada, there shall be permanent air supply opening(s) having a total cross-sectional area of not less
than 1 in.
2
of free area per 30,000 BTUH (70 mm
2
per kW) of the total rated input. The location of the
opening(s) shall not interfere with the intended purpose of the opening(s) for the ventilation air.
3. In cold climates, and to mitigate potential freeze-up, Raypak highly recommends the installation of a motor-
ized sealed damper to prevent the circulation of cold air through the heater during the non-operating hours.
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