ADOPTS WITH AMENDMENTS:

UPC 2018

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(The content of this Appendix is based on Annex I of NFPA 54)

This appendix provides general guidelines for the sizing of combination indoor and outdoor combustion and ventilation air openings.
Determine the required combination of indoor and outdoor combustion air opening sizes for the following appliance installation example.

TABLE J 101.2
STANDARD METHOD: REQUIRED VOLUME, ALL APPLIANCES*
[NFPA 54: TABLE A.9.3.2.1]

APPLIANCE INPUT
(Btu/h)
REQUIRED VOLUME
(cubic feet)
5000 250
10 000 500
15 000 750
20 000 1000
25 000 1250
30 000 1500
35 000 1750
40 000 2000
45 000 2250
50 000 2500
55 000 2750
60 000 3000
65 000 3250
70 000 3500
75 000 3750
80 000 4000
85 000 4250
90 000 4500
95 000 4750
100 000 5000
105 000 5250
110 000 5500
115 000 5750
120 000 6000
125 000 6250
130 000 6500
135 000 6750
140 000 7000
145 000 7250
150 000 7500
160 000 8000
170 000 8500
180 000 9000
190 000 9500
200 000 10 000
210 000 10 500
220 000 11 000
230 000 11 500
240 000 12 000
250 000 12 500
260 000 13 000
270 000 13 500
280 000 14 000
290 000 14 500
300 000 15 000

For SI units: 1000 British thermal units per hour = 0.293 kW, 1 cubic foot = 0.0283 m3

Example Installation: A fan-assisted furnace and a draft-hood-equipped water heater with the following inputs are located in a 15 foot by 30 foot (4572 mm by 9144 mm) basement with an 8 foot (2438 mm) ceiling. No additional indoor spaces can be used to help meet the appliance combustion air needs.

Fan-Assisted Furnace Input: 100 000 British thermal units per hour (Btu/h) (29 kW)

Draft Hood-Equipped Water Heater Input: 40 000 Btu/h (11.7 kW)

Solution:

(1)   Determine the total available room volume. Appliance room volume:
15 feet by 30 feet (4572 mm by 9144 mm) with an 8 foot (2438 mm) ceiling = 3600 cubic feet (101.94 m3)

(2)   Determine the total required volume. The standard method to determine combustion air is used to calculate the required volume. The combined input for the appliances located in the basement is calculated as follows:

100 000 Btu/h (29 kW) + 40 000 Btu/h (11.7 kW) = 140 000 Btu/h (41 kW)

The standard method requires that the required volume be determined based on 50 cubic feet per 1000 Btu/h (4.83 m3/kW). Using Table J 101.2, the required volume for a 140 000 Btu/h (41 kW) water heater is 7000 cubic feet (198.22 m3).

Conclusion: The indoor volume is insufficient to supply combustion air since the total of 3600 cubic feet (101.94 m3) does not meet the required volume of 7000 cubic feet (198.22 m3). Therefore, additional combustion air shall be provided from the outdoors.

(3)   Determine ratio of the available volume to the required volume:

(4)   Determine the reduction factor to be used to reduce the full outdoor air opening size to the minimum required based on the ratio of indoor spaces:

1.00 — 0.51 (from Step 3) = 0.49

(5)   Determine the single outdoor combustion air opening size as through all combustion air is to come from outdoors. In this example, the combustion air opening directly communicates with the outdoors:

(6)   Determine the minimum outdoor combustion air opening area:
Outdoor opening area = 0.49 (from Step 4) × 47 square inches (0.03 m2) = 23 square inches (0.01 m2)

Section 506.5.3(3) requires the minimum dimension of the air opening should be not less than 3 inches (76 mm).

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