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. � <br /> Diredions-The Minnesota Fuel Gas Code method to calculate to size of a required combustion air opening,is called the Known Air <br /> Infihration 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:Comp�ete vented combustion appliance information. <br /> Furnace/Boiler: 80000 <br /> reft Hood �an Assisted �irect Vent Input: Btu/hr or Power Vent <br /> water Heater: 40000 <br /> raft Hood �Fan Assisted �ired VeM Input: Btu/hr or Power Vent <br /> Step 2:Calculate the volume of the Combustion Appliance Space(CAS)containing combustion appliances. <br /> The CAS includes all spaces connected to one another by code compliant openings. CAS volume: 720 fta <br /> LxWxH 9 L 10 W 8�H <br /> Step 3:Determine Air Changes per Hour(ACH)i <br /> Default ACH values have been incorporeted 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 COUNIT DIRECT VEMT APPIIANCES) <br /> 4a.5Wndard 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 Requlred TRV: ft3 <br /> Volume(TRV) <br /> If CAS Volume(from Step 2)ts greo ter tha n TRV then no outdoor openings are needed. <br /> if CAS Volume(from Step 2)1 s less th an TRV then go to STEP 5. <br /> 4b.Known Air Infiltratfon Rate(KAIR)Method iD0 NOT COUNT DIRECT VENT APPUANCES) <br /> Total Btu/hr input of all fan-assisted and power veM appliances Input: � Btu/hr <br /> Use Fan-Assisted App�iances column in Table E-1 to find RVFA: `�OOO ft� <br /> Required Volume fan Assisted(RVFA) <br /> Total Btu/hr input of all Natural draft appllances Input: � Btu/hr <br /> Use Natural draft Appliances column in Table E-1 to find RVNFA: � ft3 <br /> Required Volume Natural draft appliances{RVNDA) <br /> Total Re uired Volume RV =RVFA+RVNDA TRV= �OOO + � _ �O�O TRV ftv <br /> Step 5:Calculate the ratio of available interior volume to the total required volume. <br /> Ratio=CAS Volume(from Step 2)d!vlded by TRV(from Step 4a or Step 4b) <br /> Ratio= 720 / 3000 = 0.24 <br /> Step 6:Calculate Reduction factor(RF). <br /> RF=lminus Ratio RF=1- 0.24 = 0•76 <br /> Step 7:Calculate single outdoor opening as if all combustion air is from outside. 40000 <br /> Total Btu/hr input of all Combustion Appliances in the same CAS Input: Btu/hr <br /> (EXCEPT DIRECT VENT) <br /> Combustion Air Opening Area(CAOA): ,1 - ��.�� <br /> Total Btu/hr d!v!d ed by 3000 Btu/hr per inx CApA= `'tOOOO �3t900 Btu/hr per inz- (nx <br /> Step 8:Calculate Minimum CAOA. <br /> Minimum CAOA=CAOA mukip!!ed 6y RF Mlnimum CAOA= 13.33 x Q.76 = 10.�3 �^� <br /> Step 9:Calculate Combustion Air Opening Diameter(CAOD) <br /> CAOD=1.13 m uhtpped by the sq u a re root of Minimum GAOA CAOD=1.13 V Minimum CAOA= 3'S9 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.Follow procedures in Section <br /> G304. <br />