Carrier 58HDX - Indoor Combustion Air (Unconfined Space); Standard and Known-Air-Infiltration Rate Methods

d. Vertical duct openings or openings directly communic-
ating with the outdoors require 1 square inch of free
area per 4,000 BTUH (5.5 cm2/kW) for combined in-
put of all gas appliances in the space (see Table 1).
3. When one permanent outdoor opening is used, the opening
requires:
a. 1 sq. in of free area per 3,000 BTUH (7 cm2/kW) for
combined input of all gas appliances in the space (see
Table 1) and
b. not less than the sum of the areas of all vent connect-
ors in the space.
The opening shall commence within 12” (305 mm) of the top of
the enclosure. Appliances shall have clearances of at least 1” (25
mm) from the sides and back and 6" from the front. 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 communicate with the
outdoors.
4. Combination of Indoor and Outdoor Air shall have:
a. Indoor openings that comply with the Indoor Com-
bustion Air Method below and
b. Outdoor openings located as required in the Outdoor
Combustion Air Method above and
c. Outdoor openings sized as follows.
(1.) Calculate the Ratio of all Indoor Space volume
divided by required volume for Indoor Combus-
tion Air Method.
(2.) Outdoor opening size reduction Factor is 1 minus
the Ratio in 1) above.
(3.) Minimum size of Outdoor openings shall be the
size required in Outdoor Combustion Air Meth-
od above multiplied by reduction Factor.
Table 1 — Free Area
BTUH Minimum Free Area Required for Each Opening or Duct to Outdoors
Input
Two
Horizontal
Ducts
Single
Opening
Two
Vertical
Ducts
or
Open-
(cain.
/4.000
Rating (sq. in./2,000 BTUH) (sq. in./3,000 BTUH) (eq, in,/ 4,600 BTUH) TBTUH)
60,000 30 sq. in. (194 cm?) 20 sq. in. (129 cm?) 15 sq. in. (97 cm?) 5" (127 mm)
80,000 40 sq. in. (258 cm?) 26.7 sq. in. (172 cm?) 20.0 sq. in. (129 cm2) 5" (127 mm)
100,000 50 sq. in. (322 cm2) 33.3 sq. in. (215 cm2) 25 sq. in. (161 cm2) 6” (152 mm)
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
Indoor Combustion Air (Unconfined Space)
CARBON MONOXIDE POISONING HAZARD
Failure to follow this warning could result in personal injury or
death.
Most homes will require additional air from outdoors for
combustion and ventilation. A space with at least 50 cubic
feet per 1,000 Btuh (4.8 M?/kW) Input rating or homes with
tight construction may need outdoor air, supplied through
ducts, to supplement air infiltration for proper combustion and
ventilation of flue gasses.
Standard and Known- Air- Infiltration Rate Methods
© NFPA & AGA
Indoor air is permitted for combustion and ventilation, if the
Standard or Known-Air-Infiltration Rate Method is used.
The Standard Method may be used, if the space has no less
volume than 50 cubic feet per 1,000 BTUH (4.8 M3/kW) input
rating for all gas appliances installed in the space. The standard
method permits indoor air to be used for combustion and
ventilation air.
The Known Air Infiltration Rate Method shall be used if the
infiltration rate is known to be less than 0.40 air changes per hour
(ACH) and equal to or greater than 0.10 ACH. Infiltration rates
greater than 0.60 ACH shall not be used. The minimum required
volume of the space varies with the number of ACH and shall be
determined per Table 2 or Equations 1 and 2. Determine the
minimum required volume for each appliance in the space, and
add the volumes together to get the total minimum required
volume for the space.
4 WARNING
CARBON MONOXIDE POISONING HAZARD
Failure to supply additional air by means of ventilation grilles
or ducts could result in personal injury or death.
An unconfined space or homes with tight construction may not
have adequate air infiltration for proper combustion and
ventilation of flue gasses. Most homes will require additional
air.
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