16 Page
Determine type of ventilation
1. Direct to outdoors
2.
3. Horizontal ducts
4. Single opening (not recommended; must be at least 100 in
2
(6.5 cm
2
3
(1.42 m
3
5. From a larger room inside the house (not recommended – refer to "Calculate the air volume of the room"
above to determine if the combined volume of the rooms may be adequate).
Determine minimum free area required for each vent opening
from “Before beginning”) and the type of vent used. Table 1 provides the minimum free area for each vent opening
Calculate minimum size of vent openings and ducts
vents use louvers or grilles to protect the opening. The louver or grill itself blocks some of the free area, so the open-
ing may need to be larger to meet the minimum free area requirements.
2
(645 cm
2
) of free area would need
134 in
2
(865 cm
2
2
2
).
Each vent opening must be no smaller than 100 in
2
(645 cm
2
).
Rectangular ducts must have a minimum dimension of no less than 3 in (76 mm).
All screens must have mesh ¼” or larger.
-
Check that air source is clean and free of chemicals
-
See graphics on next page.
Table 1
indoor spaces.
Opening Source Minimum Free Area
Direct to outdoors*
1 in
2
(6.5 cm
2
) per 4,000 BTU/hr (see Figure 1, 2)
1 in
2
(6.5 cm
2
) per 4,000 BTU/hr (see Figure 3)
Horizontal ducts
1 in
2
(6.5 cm
2
) per 2,000 BTU/hr (see Figure 4)
Single Opening
1 in
2
(6.5 cm
2
) per 3,000 BTU/hr (see Figure 5)
Two permanent openings
to another room**
1 in
2
(6.5 cm
2
) per 1,000 Btu/hr (see Figure 6)
Opening: 100 in
2
(645 cm
2
) MIn
Minimum dimension of air openings:
no less than 3 in (76 mm)
an outside wall.
-
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