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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 /> 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/Boiler: 80000 <br /> raft 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 Appliance Space(CAS)containing combustion appliances. ,�79,1 <br /> The CAS includes all spaces conneded to one another by code comptiant openings. CAS volume: ft3 <br /> LxWxH 16 L 14 W�H <br /> Step 3:Determine Air Changes per Hour(ACH)1 <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 COUNT DIRECT VENT APPLIANCES) <br /> 4a.5tandard 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 greo ter ih an TRV then no outdoor openings are needed. <br /> If CAS Volume(from Step 2)is less th an TRV then go to STEP 5. <br /> 4b.Known Air Infiltretion Rate(KAIR)Method(DO NOT COUNT DIRECT VENT APPLIANCES) <br /> Total Btu/hr input of all fan-assisted and power vent appliances Input: ��� Btu/hr <br /> Use Fan-Assisted Appliances column in Table E-1 to find RVFA: 3000 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: � fta <br /> Required Volume Natural dreft appliances(RVNDA) <br /> Total Re uired Volume TRV =RVFA+RVNDA TRV= �OOO + O _ 3000 TRV ft3 <br /> Step 5:Calculate the retio of available interior volume to the total required volume. <br /> Ratio=CAS Volume(from Step 2)di vlded by TRV(from Step 4a or Step 4b) <br /> Ratio= 1792 / 3000 = 0.60 <br /> Step 6:Calculate Reduction Factor(RF�. <br /> RF=lminus Ratio RF=1- O.VO = O•TO <br /> Step 7:Calculate single outdoor opening as ff 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): <br /> Total Btu/hr d i vi d ed by 3000 Btu/hr per inz CAOA= 40000 �3000 Btu/hr per inz= �3•33 inz <br /> Step 8:Calculate Minimum CAOA. <br /> MinimumCAOA=CAOAmukiplied by Rf MinimumCAOA= �3.33 x o.40 = 5.37 ��� <br /> Step 9:Calculate Combustion Air Opening Diameter(CAOD) <br /> CAOD=1.13 m ultiplied by the sq u o►e ►oot of Minimum CAOA CAOD=1.13�Minimum CAOA= 2'62 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 />