58HDV
Table 1 |
| Free Area |
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| Minimum Free Area Required for Each Opening or Duct to Outdoors |
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BTUH (kW) |
| Two Horizontal Ducts |
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| Single Opening |
| Two Vertical Ducts or | Round Duct |
Input Rating |
| BTUH (kW) |
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| BTUH (kW) |
| Openings | BTUH (kW) |
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| sq. in./2,000(1 cm2/.09) |
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| sq. in./3,000 (1 cm2/.135) |
| BTUH (kW) | sq. |
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| sq. in./4,000(1 cm2/.18) | in./4,000(6.5cm2/.18) | ||
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40,000 (11.72) |
| 20 sq. in. (129 cm2) |
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| 13.34 sq. in. (86 cm2) |
| 10 sq. in. (65 cm2) | 4″ (101.6mm) |
50,000 (14.65) |
| 25 sq. in. (161 cm2) |
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| 16.7 sq. in. (108 cm2) |
| 12.5 sq. in. (81 cm2) | 4″ (101.6mm) |
60,000 (17.58) |
| 30 sq. in. (194 cm2) |
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| 20 sq. in. (129 cm2) |
| 15 sq. in. (97 cm2) | 5″ (127mm) |
75,000 (21.98) |
| 37.5 sq. in. (242 cm2) |
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| 25 sq. in. (161 cm2) |
| 18.75 sq. in. (121 cm2) | 5″ (127mm) |
80,000 (23.45) |
| 40 sq. in. (258 cm2) |
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| 26.7 sq. in. (172 cm2) |
| 20 sq. in. (129 cm2) | 5″ (127mm) |
100,000 (29.31) |
| 50 sq. in. (322 cm2) |
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| 33.3 sq. in. (215 cm2) |
| 25 sq. in. (161 cm2) | 6″ (152.4mm) |
125,000 (36.63) |
| 62.50 sq. in. (403 cm2) |
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| 41.7 sq. in. (269 cm2) |
| 31.25 sq. in. (202 cm2) | 7″ (177.8mm) |
EXAMPLE: Determining Free Area |
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Furnace |
| Water Heater |
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| Total Input |
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100,000 | + | 30,000 | = | (130,000 ÷ 4,000) | = | 32.5 Sq. In. Vertical |
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29.31 |
| 8.8 |
| (38.11 ÷ .18) | = | 210 cm2 Vertical |
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Furnace |
| Water Heater |
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| Total Input |
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100,000 | + | 30,000 | = | (130,000 ÷ 2,000) | = | 65 Sq. In. Horizontal |
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29.31 |
| 8.8 |
| (38.11 ÷ .09) | = | 423 cm2 Horizontal |
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Indoor Combustion Air (Unconfined Space)
!WARNING
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 (1.43M) per 1,000 (2.33 cm2/kW) Btuh 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
The Standard Method may be used, if the space has no less volume than 50 cubic feet per 1,000 BTUH 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.
!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.
| Table 2 |
| MINIMUM SPACE VOLUME FOR 100% COMBUSTION AND VENTILATION AIR FROM INDOORS | |||||||||
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| Other Than Fan- Assisted Total |
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| 30,000 BTU | 40,000 BTU | 50,000 BTU | 50,000 BTU | 75,000 | 100,000 BTU | 125,000 BTU | |||
ACH |
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| (8,790 kW) | (11,720 kW) | (14,650 kW) | (14,650 kW) | (21,975 kW) | (29,300 kW) | (36,625 kW) | |||
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| ft3 (m3) |
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0.60 |
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| 1,050 (29.7) | 1,400 (39.2) | 1,750 | (49) | 1,250 (35) | 1,875 (52.5) | 2,500 | (70) | 3,125 (87.5) | |
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0.50 |
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| 1,260 (35.3) | 1,680 (47.04) | 2,100 (58.8) | 1,500 (42) | 2,250 (63) | 3,000 | (84) | 3,750 (105) | ||
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0.40 |
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| 1,575 (44.1) | 2,100 (58.8) | 2,625 (73.5) | 1,875 (52.5) | 2,813 (78.8) | 3,750 (105) | 4,688 (131.3) | |||
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0.30 |
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| 2,100 (58.8) | 2,800 (78.4) | 3,500 | (98) | 2,500 (70) | 3,750 (105) | 5,000 (140) | 6,250 (175) | ||
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0.20 |
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| 3,150 (88.2) | 4,200 (117.6) | 5,250 (147) | 3,750 (105) | 5,625 (157.5) | 7,500 (210) | 9,375 (262.5) | |||
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0.10 |
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| 6,300 (176.4) | 8,400 (235.2) | 10,500 | (294) | 7,500 (210) | 11,250 (315) | 15,000 | (420) | 18,750 (525) | |
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0.00 |
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| NP | NP | NP | NP | NP | NP | NP | |||
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ACH = Air Changes per Hour NP = Not Permitted
Table 2 Minimum Space Volumes were determined by using the following equations from the National Fuel Gas Code ANSI Z223.1/NFPA
1. For appliances other than |
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a draft | Required Volume other |
| 21 ft3 | I | other | |||
lowing equation: | ² |
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| 1000 Btu / hr | ||||||
ACH |
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10