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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 construcYion,46 of step 4 is required to 6e filled ouf. <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 L Complete vented combustion appliance information. <br /> Furnace/Boiler. <br /> _Draft Hood Fan Assisted �Direct Vent Input � ���Btu/hr <br /> or Power Vent <br /> Water Heater: <br /> _Draft Nood Fan Assisted _Oirect Vent Input: ����� gtu/hr <br /> or Power Vent <br /> Step 2:Calculate the volume of the Combustion Appliance Space(CAS)containing combustion appliances. �1 <br /> The CAS indudes all spaces connected to one another by code compliant openin f � CAS volume: -/ ��� ft3 <br /> LxWxH y�L �� 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 46�KAIR Method). <br /> If�he year of cpnstruction or ACH is not known,use method 4a(Standard Me.thod). <br /> Step 4:Determine Required Volume for Combustion Air.(DO NOT COUNT DIRECT VENT APPUANCES) <br /> 4a.Standard Method <br /> Total Btu/hr input of all combustion appliances Input: 8tu/hr <br /> Use Standard Method column in Table E-1 to find Total Required TRV: ft' <br /> Volume(TRVj <br /> If CAS Volume(from Step 2)is greoter thon TRV then no outdoor openings are needed. <br /> If CAS Voluine(from Step 2)is less than TRV then go to STEP S. <br /> 46.K�own Air Inlill�ahon Rate(KAIR)Method(DO NOT COUNT DIRECT VENT APPUANCES� <br /> Total Btu/hr input of all fan-assisted and power vent appliances Input: ��� �o� g�u/hr <br /> '�C-_'— <br /> Use Fan-Assis[ed Appiiances column in Table E�1 to find RVFA: ��B� h' <br /> Required Volume Fan Assisted(RVFAJ <br /> � <br /> Total Btu/hr input of all Natural dreft appliances Input: Btu/hr <br /> Use Natural draft Appliances column in Table E-1 to find RVNFA: � h' <br /> Required Volume rvatural draft appliances(RVNDA) <br /> / 7�� <br /> 7ota1 Required Volume(TRV)=RVFA+RVNDA TRV= 77 �� + (� - < � p� TRV ft' <br /> If CI�S Volume(from Step 2)is greater than TRV then no ou[door openings are needed. <br /> If CAS Volume(from Step 2)is less than TRV then go to STEP 5. <br /> Step 5:Calculate the ratio of avallable interior vo{ume to the total required volume. <br /> Ratio=CAS Volume(from Step 2J divided by TRV(from Step 4a or Step 4b) � <br /> Ratio= �j� �p = < <br /> Step 6:Calculate Reduction factor�RF). <br /> RF=1 minus Ratio RF_=1- � � _ .. 7 <br /> Step 7:Calculate single outdoor opening as if all combustion air is from outside. <br /> Total Btu/hr input of all Combustion Appliances in the same CAS Input: l��O1'�3tu/hr <br /> (EXCEP7 DIRECT VENT) � <br /> Combus[ion Air Opening Area(CAOA): � <br /> Total Btu/hr divided by 3000 6tu/hr per in3 CAOA= �� �3000 Btu/hr per in'= in2 <br /> Step 8:Calculate Mirtimum CAOA. <br /> Minimum CAOA=CAOA multiplied 6y RF Minimum CAOA= �� x = ;�' � � . �/ <br /> Step 9:Calculate Combustion Air Opening Diameter(CAOD) <br /> CAOD=1.13 multiplied by the squore root oj Minimum CAOA CAOD=1.13� Minimum CAOA= in.diameter <br /> go up one inch in size if using flex duct <br /> 1 Ii desired,ACH can be determined using ASHRAE calculation or blower door test.Follow procedures in Section <br /> G304. <br /> Page 5 oi 6 <br />