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Directions-The Minnesota Fuel Gas Code method to calculate to size of a required combustion air opening,is called the Known Air <br /> Infiltration Rate Method.For new construction,4b of step 4 is required to be filled out. <br /> IFGC Appendix E,Worksheet E-1 <br /> Residential Combustion Air Calculation Method <br /> (for Furnace,Boiler,and/or Water Heater in the Same Space) <br /> Step i:Complete vented combustion appliance information. <br /> Furnace/Boiler: 60000 <br /> reft Hood �an Assisted �irect Vent Input: Btu/hr or Power Vent <br /> water Heater: 40000 <br /> reft Hood �Fan Assisted �irect Vent Input: Btu/hr or Power Vent <br /> Step 2:Calculate the volume of the Combustion Appiiance Space(CAS)containing combustion appliances. <br /> The CAS includes all spaces connected to one another by code compliant openings. CAS volume: 640 ft; <br /> LxWxH �L 10 W�H <br /> Step 3:Determine Air Changes per Hour(ACH)1 <br /> Default ACH values have been incorporated into Table E-1 for use with Method 4b(KAIR Method�.If the year of construction or ACH is not known,use <br /> method 4a(Standard Method). <br /> Step 4:Determine Required Volume for Combustion Air.(DO NOT COUNT DIRECT VENT APPLIANCES) <br /> 4a.Standard Method <br /> Total Btu/hr input of all combustion appliances Input: Btu/hr <br /> Use Standard Method column in Table E-1 to find Total Required TRV: ft3 <br /> Volume(TRV) <br /> If CAS Volume(from Step 2)is yre a t er th a n TRV then no outdoor openings are needed. <br /> If CAS Volume(from Step 2)!s less th on TRV then go to STEP 5. <br /> 4b.Known Air Infiltration Rate(KAIR)Method(DO NOT COUNT D�RECT VENT APPLIANCES) <br /> Total etu/hr input of all fan-assisted and power vent appliances Input: �000 Btu/hr <br /> Use Fan-Assisted Appliances column in Table E-1 to find RVFA: `�OOO ft3 <br /> Required Volume Fan Assisted(RVFA) <br /> Total Btu/hr input of all Natural dreft appliances Input: O Btu/hr <br /> Use Natural dreft Appliances column in Table E-1 to find RVNFA: � ft� <br /> Required Volume Natural dreft appliances(RVNDA) <br /> Total Re uired Volume TRV =RVFA+RVNDA TRV= �000 + O _ �000 TRV ft3 <br /> Step 5:Calculate the ratio of available interior volume to the total required volume. <br /> Ratio=CAS Volume(from Step 2)divided by TRV(from Step 4a or Step 4b) <br /> Racio= 640 � 3000 = 0.21 <br /> Step 6:Calcutate Reduction Factor(RF). <br /> RF=1minus Ratio RF=1- 0•21 = �.79 <br /> Step 7:Calculate single outdoor opening as if all combustion air is from outside. 40000 <br /> Total etu/hr input of all Combustion Appliances in the same CAS Input: Btu/hr <br /> (EXCEPT DIRECT VENT) <br /> Combustion Air Opening Area(CAOA): A <br /> Total Btu/hr d i vi d ed by 3000 Btu/hr per in: CAOA= `+OOOO /3000 Btu/hr per in2= �3•33 in: <br /> Step 8:Calculate Minimum CAOA. <br /> Minimum CAOA=CAOA multiplied by RF Minimum CAOA= I 3.33 x Q.79 = 10.49 im <br /> Step 9:Calculate Combustion Air Opening Diameter(CAOD) <br /> CAOD=1.13 m u/tiplled by the squ a re root of Minimum CAOA CAOD=1.13 V Minimum CAOA= 3.65 in.diameter go up one inch in size <br /> if using flex duct <br /> 1 If desired,ACH can be determined using ASHRAE calculation or blower door test.Foilow procedures in Section <br /> G304. <br />