# F 102.0 Examples Using Common Venting Tables

Solution:

Table 803.2(2) shall be used to size single-wall metal vent connectors attached to Type B vertical vents. In the vent connector capacity portion of Table 803.2(2), find the row associated with a 30 foot (9144 mm) vent height. For a 2 foot (610 mm) rise on the vent connector for the water heater, read the shaded columns for draft hood-equipped appliances to find that a 3 inch (76 mm) diameter vent connector has a capacity of 37 000 Btu/h (10.8 kW). Therefore, a 3 inch (76 mm) single-wall metal vent connector shall be used with the water heater. For a draft hood-equipped furnace with a 3 foot (914 mm) rise, read across the row to find that a 5 inch (127 mm) diameter vent connector has a maximum capacity of 120 000 Btu/h (35 kW) (which is too small for the furnace), and a 6 inch (152 mm) diameter vent connector has a maximum vent capacity of 172 000 Btu/h (50 kW). Therefore, a 6 inch (152 mm) diameter vent connector shall be used with the 150 000 Btu/h (44 kW) furnace. Since both vent connector horizontal lengths are less than the maximum lengths listed in Section 803.2.1, the table values shall be used without adjustments.

For SI units: 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW

**FIGURE F 102.1COMMON VENTING TWO DRAFT HOOD-EQUIPPED APPLIANCESEXAMPLE 4**

In the common vent capacity portion of Table 803.2(2), find the row associated with a 30 foot (9144 mm) vent height and read over to the NAT + NAT portion of the 6 inch (152 mm) diameter column to find a maximum combined capacity of 257 000 Btu/h (75 kW). Since the two appliances total 185 000 Btu/h (54 kW), a 6 inch (152 mm) common vent shall be used.

Solution:

Water Heater Vent Connector Diameter. Since the water heater vent connector horizontal length of 4 feet (1219 mm) is less than the maximum value listed in Table 803.2(2), the venting table values shall be used without adjustment. Using the Vent Connector Capacity portion of Table 803.2(2), read down the Total Vent Height (*H*) column to 30 feet (9144 mm) and read across the 2 feet (610 mm) Connector Rise (*R*) row to the first Btu/h rating in the NAT Max column that is equal to or exceeding the water heater input rating. The table shows that a 3 inch (76 mm) vent connector has a maximum input rating of 37 000 Btu/h (10.8 kW). Although this rating is exceeding the water heater input rating, a 3 inch (76 mm) vent connector is prohibited by Section 803.2.18. A 4 inch (102 mm) vent connector has a maximum input rating of 67 000 Btu/h (19.6 kW) and is equal to the draft hood outlet diameter. A 4 inch (102 mm) vent connector is selected. Since the water heater is equipped with a draft hood, there are no minimum input rating restrictions.

Furnace Vent Connector Diameter. Using the Vent Connector Capacity portion of Table 803.2(2), read down the Total Vent Height (*H*) column to 30 feet (9144 mm) and across the 3 feet (914 mm) Connector Rise (*R*) row. Since the furnace has a fan-assisted combustion system, find the first FAN Max column with a Btu/h rating exceeding the furnace input rating. The 4 inch (102 mm) vent connector has a maximum input rating of 119 000 Btu/h (34.9 kW) and a minimum input rating of 85 000 Btu/h (24.9 kW).

The 100 000 Btu/h (29 kW) furnace in this example falls within this range, so a 4 inch (102 mm) connector shall be permitted. Since the furnace vent connector horizontal length of 6 feet (1829 mm) is less than the maximum value listed in Section 803.2.1, the venting table values shall be used without adjustment. Where the furnace had an input rating of 80 000 Btu/h (23.4 kW), then a Type B vent connector shall be needed in order to meet the minimum capacity limit.

Common Vent Diameter. The total input to the common vent is 135 000 Btu/h (40 kW). Using the Common Vent Capacity portion of Table 803.2(2), read down the Vent Height (*H*) column to 30 feet (9144 mm) and across this row to find the smallest vent diameter in the FAN + NAT column that has a Btu/h rating equal to or exceeding 135 000 Btu/h (40 kW). The 4 inch (102 mm) common vent has a capacity of 132 000 Btu/h (39 kW) and the 5 inch (127 mm) common vent has a capacity of 202 000 Btu/h (59 kW). Therefore, the 5 inch (127 mm) common vent shall be used in this example.

Summary: In this example, the installer shall use a 4 inch (102 mm) diameter, single-wall metal vent connector for the water heater and a 4 inch (102 mm) diameter, single-wall metal vent connector for the furnace. The common vent shall be a 5 inch (127 mm) diameter Type B vent.

For SI units: 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW

**FIGURE F 102.2COMMON VENTING A DRAFT HOOD-EQUIPPED WATER HEATER WITH A FAN-ASSISTED FURNACE INTO A TYPE B DOUBLE-WALL COMMON VENTEXAMPLE 5(a)**

Solution:

Table 803.2(4) is used to size common venting installations involving single-wall connectors into masonry chimneys.

Water Heater Vent Connector Diameter. Using Table 803.2(4), Vent Connector Capacity, read down the Vent Height *(H)* column to 30 feet (9144 mm), and read across the 2 feet (610 mm) Connector Rise *(R)* row to the first Btu/h rating in the NAT Max column that is equal to or exceeding the water heater input rating. The table shows that a 3 inch (76 mm) vent connector has a maximum input of 31 000 Btu/h (9 kW), while a 4 inch (102 mm) vent connector has a maximum input of 57 000 Btu/h (16.7 kW). A 4 inch (102 mm) vent connector shall be used.

Furnace Vent Connector Diameter. Using the Vent Connector Capacity portion of Table 803.2(4), read down the total Vent Height (*H*) column to 30 feet (9144 mm) and across the 3 feet (914 mm) Connector Rise (*R*) row. Because the furnace has a fan-assisted combustion system, find the first FAN Max column with a Btu/h rating exceeding the furnace input rating. The 4 inch (102 mm) vent connector has a maximum input rating of 127 000 Btu/h (37 kW) and an input rating of not less than 95 000 Btu/h (27.8 kW). The 100 000 Btu/h (29 kW) furnace in this example falls within this range, so a 4 inch (102 mm) connector shall be permitted.

Masonry Chimney. From Table F 102.3, the equivalent area for a nominal liner size of 8 inches (203 mm) by 12 inches (305 mm) is 63.6 of a square inches (0.041 m^{2}). Using Table 803.2(4), Common Vent Capacity, read down the FAN + NAT column under the Minimum Internal Area of Chimney value of 63 to the row for 30 foot (9144 mm) height to find a capacity value of 739 000 Btu/h (217 kW). The combined input rating of the furnace and water heater, 135 000 Btu/h (40 kW), is less than the table value so this is an acceptable installation.

Section 803.2.17 requires the common vent area to not exceed seven times the smallest listed appliance categorized vent area, flue collar area, or draft hood outlet area. Both appliances in this installation have 4 inch (102 mm) diameter outlets. From Table F 102.3, the equivalent area for an inside diameter of 4 inches (102 mm) is 12.2 of a square inches (0.008 m^{2}). Seven times 12.2 equals 85.4, which is exceeding 63.6, so this configuration is acceptable.

**TABLE F 102.3 MASONRY CHIMNEY LINER DIMENSIONS WITH CIRCULAR EQUIVALENTS***

NOMINAL LINER SIZE (Inches) | INSIDE DIMENSIONS OF LINER (Inches) | INSIDE DIAMETER OR EQUIVALENT DIAMETER (Inches) | EQUIVALENT AREA (Square Inches) |
---|---|---|---|

4 × 8 | 2^{1}/_{2} × 6^{1}/_{2} | 4.0 | 12.2 |

5.0 | 19.6 | ||

6.0 | 28.3 | ||

7.0 | 38.3 | ||

8 × 8 | 6^{3}/_{4} × 6^{3}/_{4} | 7.4 | 42.7 |

8.0 | 50.3 | ||

8 × 12 | 6^{1}/_{2} × 10^{1}/_{2} | 9.0 | 63.6 |

10.0 | 78.5 | ||

12 × 12 | 9^{3}/_{4} × 9^{3}/_{4} | 10.4 | 83.3 |

11.0 | 95.0 | ||

12 × 16 | 9^{1}/_{2} × 13^{1}/_{2} | 11.8 | 107.5 |

12.0 | 113.0 | ||

14.0 | 153.9 | ||

16 × 16 | 13^{1}/_{4} × 13^{1}/_{4} | 14.5 | 162.9 |

15.0 | 176.7 | ||

16 × 20 | 13 × 17 | 16.2 | 206.1 |

18.0 | 254.4 | ||

20 × 20 | 16^{3}/_{4} × 16^{3}/_{4} | 18.2 | 260.2 |

20.0 | 314.1 | ||

20 × 24 | 16^{1}/_{2} × 20^{1}/_{2} | 20.1 | 314.2 |

22.0 | 380.1 | ||

24 × 24 | 20^{1}/_{4} × 20^{1}/_{4} | 22.1 | 380.1 |

24.0 | 452.3 | ||

24 × 28 | 20^{1}/_{4} × 24^{1}/_{4} | 24.1 | 456.2 |

28 × 28 | 24^{1}/_{4} × 24^{1}/_{4} | 26.4 | 543.3 |

27.0 | 572.5 | ||

30 × 30 | 25^{1}/_{2} × 25^{1}/_{2} | 27.9 | 607.0 |

30.0 | 706.8 | ||

30 × 36 | 25^{1}/_{2} × 31^{1}/_{2} | 30.9 | 749.9 |

33.0 | 855.3 | ||

36 × 36 | 31^{1}/_{2} × 31^{1}/_{2} | 34.4 | 929.4 |

36.0 | 1017.9 |

For SI units, 1 inch. = 25.4 mm, 1 square inch = 0.000645 m^{2}

* Where liner sizes differ dimensionally from those shown in this table, equivalent diameters shall be permitted to be determined from published tables for square and rectangular ducts of equivalent carrying capacity or by other engineering methods.

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