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GS110 DIRECT VENT BOILER INSTALLATION AND OPERATION INSTRUCTIONS Page 5
When calculating the free area necessary to meet the
make-up air requirements of the enclosure,
consideration must be given to the blockage effects of
louvers, grills and screens.
Screens must have a minimum mesh size of 1/4"
(6.4mm). If the free area through a louver or grill is not
known ducts should be sized per Table 1.
Table 1 - Combustion Air Duct Sizing
Figure 3 - Horizontal Positive Pressure Venting Using Inside Combustion Air (Cat. III)
Figure 4 - Vertical Negative Pressure Masonry Chimney System Using Inside Combustion Air (Cat. I)
Input Btuh
Wooden
Louvers
Input Btuh
Metal
Louvers
Input Btuh
1/4” Wire
Screen Mesh
FreshAir
Duct Size
36,000
64,000
96,000
128,000
108,000
192,000
288,000
384,000
144,000
256,000
384,000
512,000
3” x 12”
8” x 8”
8” x 12”
8-1/2” x 16”