7
441 01 5001 00
5. When sizing grille or louver, use the free area of opening. If
free area is
NOT
stamped or marked on grill or louver, as-
sume a 20% free area for wood and 60% for metal.
Requirements
1. Provide confined space with sufficient air for proper combus-
tion and ventilation of flue gases using horizontal or vertical
ducts or openings.
2.
Figure 4
illustrates how to provide combustion and ventila-
tion air. A minimum of two permanent openings, one inlet and
one outlet, are required.
3. One opening
MUST
be within 12
²
of the floor and the second
opening within 12
²
of the ceiling.
4. Size openings and ducts per
Table 1
.
Furnace
Furnace
Minimum One Inlet and One Outlet Air Supply is Required
May be in and Combination Shown
Inlet Air Opening Must be Within12
²
(300mm) of floor
Outlet Air Opening Must be Within12
²
(300mm) of ceiling
(1) 1 Square Inch (6cm
2
) per 4000 BTUH
(2) 1 Square Inch (6cm
2
) per 2000 BTUH
Outside Air (This is ONLY a guide. Subject to codes of country having jurisdiction.)
Figure 4
This installation NOT approved in Canada
Gas Vent
Gas Vent
Gas Vent
Gable Vent
Gable Vent
Outlet
Air (1)
Outlet Air (1)
Outlet Air (1)
Furnace
Outlet
Air (2)
Optional Inlet Air (1)
Ventilated Attic
Ventilated Attic
Ventilated Crawl Space
Inlet
Air (1)
Inlet
Air (1)
Inlet
Air (1)
Inlet
Air (2)
Inlet
Air (2)
Top Above Insulation
Top Above Insulation
Soffit Vent
Soffit Vent
5. Horizontal duct openings require 1 square inch of free area
per 2,000 BTUH of combined input for all gas appliances in
area
(
see
Table 1)
.
6. Vertical duct openings or openings directly to outside require
1 square inch of free area per 4,000 BTUH for combined input
of all gas appliances in area
(
see
Table 1).
One permanent opening, commencing within 12
²
of the top of the
enclosure, shall be permitted where the equipment has clear-
ances of at least 1
²
from the sides and back and 6
²
from the front of
the appliance. The opening shall directly communicate with the
outdoors or shall communicate through a vertical or horizontal
duct to the outdoors or spaces (crawl or attic) that freely communi-
cate with the outdoors, and shall have a minimum free area of:
·
1 sq. in per 3000 Btu per hr. of the total input rating of all equip-
ment located in the enclosure, and
·
Not less than the sum of the areas of all vent connectors in the
confined space.
Table 1
Free Area
BTUH
Minimum Free Area Required for Each Opening
BTUH
Input
Rating
Horizontal Duct
(sq. in./2,000 BTUH)
Vertical Duct or
openings to outside
(sq. in./4,000 BTUH)
Rd Duct
(sq. in. /4,000
BTUH)
50,000
25 sq. in.
12.5 sq. in.
4
²
75,000
35.5 sq. in.
18.75 sq. in.
5
²
100,000
50 sq. in.
25 sq. in.
6
²
125,000
62.5 sq. in.
31.25 sq. in.
7
²
EXAMPLE:
Determining Free Area
Furnace Water Heater Total Input
100,000
+
30,000 = (130,000
¸
4,000) = 32.5 Sq. In. Vertical
Furnace Water Heater Total Input
100,000
+
30,000 = (130,000
¸
2,000) = 65 Sq. In. Horizontal
Unconfined Space Installation
!
CARBON MONOXIDE POISONING HAZARD.
Most homes will require additional air.
Failure to supply additional air by means of
ventilation grilles or ducts could result in death
and/or personal injury.
An unconfined space or homes with tight
construction may not have adequate air infiltration
for proper combustion and ventilation of flue
gases.
An unconfined space is defined as an area having a minimum vol-
ume of 50 cubic feet per 1,000 Btuh total input rating for all gas ap-
pliances in area.
