701.4 Indoor Combustion Air. The required volume of

indoor air shall be determined in accordance with the method in Section 701.4.1 or Section 701.4.2 except that where the air infiltration rate is known to be less than 0.40 ACH (air change per hour), the method in Section 701.4.2 shall be used. The total required volume shall be the sum of the required volume calculated for appliances located within the space. Rooms communicating directly with the space in which the appliances are installed through openings not furnished with doors, and through combustion air openings sized and located in accordance with Section 701.5, are considered a part of the required volume. [NFPA 54:9.3.2]

701.4.1 Standard Method. The minimum required volume shall be 50 cubic feet per 1000 British thermal units per hour (Btu/h) (4.83 m ³ /kW). [NFPA 54:9.3.2.1] 701.4.2 Known Air Infiltration Rate Method. Where the air infiltration rate of a structure is known, the minimum required volume shall be determined as follows

[NFPA 54:9.3.2.2]: (1) For appliances other than fan-assisted, calculate

using the following Equation 701.4.2(1). [NFPA 54:9.3.2.2(1)]

[Equation 701.4.2(1)]

ACH 1000 Btu/h

21 ft3 ( I other )

[Equation 701.4.2(1)]

ACH

Required Volume other ≥ 21 ft3 (

(2) For fan-assisted appliances, calculate using the fol lowing Equation 701.4.2(2). [NFPA 54: 9.3.2.2(2)]

[Equation 701.4.2(2)]

Required Volume fan ≥ ACH 1000 Btu/h

15 ft 3 ( I fan )

Where: I other = All appliances other than fan-assisted input (Btu/h) I fan = Fan-assisted appliance input (Btu/h) ACH = Air change per hour (percent of volume of space exchanged per hour, expressed as a decimal)

For SI units: 1 cubic foot = 0.0283 m ³, 1000 British thermal units per hour = 0.293 kW

(3) For purposes of these calculations, an infiltration

rate greater than 0.60 ACH shall not be used in the equations in Section 701.4.2(1) and Section 701.4.2(2). [NFPA 54:9.3.2.2(3)]