Bard Bayrd Furnace 403293A - Manual (Page 13)

For example:
Total Input Free Area Per Opening
Btuh (square Inches)
40,000-100,000 100
120,000 120
140,000 140
b. If building is of unusually tight construc­
tion, provide a permanent opening di­
rectly communicating with the outdoors.
Opening shall have a minimum free area
of one square inch per 4000 Btuh of
total input rating for all equipment in the
enclosure.
If return air is taken directly from hall­
way or space next to furnace that com­
municates with furnace spaces, all air
for combustion must come from out­
doors.
b. All combustion and ventilation air from outdoors.
1. The furnace space must be provided with
two permanent air openings directly to the
outdoors, or by ducts to the outdoors or
spaces (attic or crawl spaces) that freely ac­
cess the outdoors. These combustion and
ventilation openings will give fresh air free
access to furnace space for combustion and
ventilation. You must also provide air suffi­
cient for all other gas appliances within fur­
nace space.
Ducts must freely access outdoors or spaces
(attic or crawl spaces) which freely access
the outdoors. Well ventilated attics or crawl
spaces usually satisfy this requirement.
2. Locate one combustion and ventilation air
operîing within 12" of top of furnace space.
Locate another within 12" of bottom of fur­
nace space.
3. When directly accessing the outdoors, each
opening must have a minimum free area of
one square inch per 4,000 Btuh of total
combined input rating of all gas appliances
within furnace space. See Figure 13A.
4. If combustion air ducts will run vertically,
ducts and each opening must have a mini­
mum free area of one square inch per 4,000
Btuh total combined input rating. You must
allow for all gas appliances within the fur­
nace space. See Figure 13B.
For example:
Total Input
Btuh
Required
Free Area per Opening
(square inches)
Suggested
Round Pipe
(inches dia.)
40,000 10.0 4
60,000 15.0 5
80,000 20.0 6
100,000 25.0 6
120,000 30.0 7
140,000 35.0 7
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