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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 1:Complete vented combustion appliance information. <br /> Furnace/soiler: ,�o0000 <br /> raft Hood �an Assisted �ired Vent Input: Btu/hr or Power Vent <br /> water Heater: 4000� <br /> raft Hood �Fan Assisted �Direct Vent 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: 990 ft3 <br /> LxWxH 10 L 11 W 9�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: fta <br /> Volume(TRV) <br /> If CAS Volume(from Step 2)is gre a ter th o n TRV then no outdoor openings are needed. <br /> If CAS Volume(from Step 2)i s less th an TRV then go to STEP 5. <br /> 4b.Known Air Infiltration Rate(KAIR)Method(DO NOT COUNT DIRECT VENT APPLIANCES) <br /> Total Btu/hr input of all fan-assisted and power vent appliances Input: 4��� 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 draft appliances Input: O 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 TRV =RVFA+RVNDA TRV= �OOO + 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)di vfded by TRV(from Step 4a or Step 4bj <br /> Ratio= ggQ � 3000 = 0.33 <br /> Step 6:Calculate Reduction Factor(RF). <br /> RF=1 mi n us Ratio RF=1- O.33 = 0.67 <br /> Step 7:Calculate single outdoor opening as if all combustion air is from ouuide. 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): <br /> Total Btu/hr d i vid ed by 3000 Btu/hr per ina CAOA= 40000 /3000 Btu/hr per in:_ �3.33 inz <br /> Step 8:Calculate Minimum CAOA. <br /> MinimumCAOA=CAOAmuliiplied by RF MinimumCAOA= �3.33 x Q.67 = 8.93 inz <br /> Step 9:Calculate Combustion Air Opening Diameter(CAOD) <br /> CAOD=1.13 m ultiplied by the sq u are root of Minimum CAOA CAOD=1.13�Minimum CAOA= 3'38 in.diameter go up one inch in size <br /> if usin�flex duct <br /> 1 If desired,ACH can be determined using ASHRAE calculation or blower door test.Follow procedures in Section <br /> G304. <br />