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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 /> Infikration 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 Caiculation Method <br /> (for Furnace,Boiler,and/or Water Heater in the Same Space) <br /> Step 1:Complete vented combustion appUance information. <br /> Furnace/Boiler: 60000 <br /> raft Hood �an Assisted �ired Vent Input: Btu/hr or Power Vent <br /> water Heater: 40000 <br /> raft Hood �Fan Assisted �irect Vent Input: Btu/hr or Power Vent <br /> Step 2:Calculate the volume of the Combustion Appliance Space{CAS)containing combustlon appliances. <br /> The C0.5 includes all spaces connected to one another by code compliant openings. CAS volume: �O ft3 <br /> LxWxH 8 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 construdion 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 pre a t er th o n TRV then no outdoor openings are needed. <br /> tf CAS Volume(from Step 2)/s less than TRV then go to STEP 5. <br /> 4b.Known Air Inflltration Rate(KAIR)Method(DO NOT COUNT OIRECT VENT APPIIANCES) <br /> Total Btu/hr input of all hn-assisted and power veM appliances Input: � Btu/hr <br /> Use Fan-Assisted AppNances column in Table E-1 to find RVFA: `�OOO � <br /> Required Volume Fan Assisted(RVFA) <br /> Total Btu/hr input of all Naturai draft appliances Input: � Btu/hr <br /> Use Natural draft Appliances column in Table E-1 to find RVNFA: � ft3 <br /> Required Volume Natural draft appHances{RVNDA) <br /> Total Re uired Volume RV =RVFA+RVNDA TRV= 3000 + O _ �00o TRV fta <br /> Step 5:Calculate the ratio of available inter(or volume to the total required volume. <br /> Ratio=CAS Volume(from Step 2)dl vided by TRV(from Step 4a or Step 4b) <br /> Ratto= �Q / 3000 = 0.21 <br /> Step 6:Calculate Reduction Factor(RF). <br /> RF=1minus Ratio RF=1- 0•21 = 0•79 <br /> Step 7:Calcu�ate single outdoor opening as if all combustion air is from outside. 40000 <br /> Total Btu/hr input of all Combustion Appliances in the same CIlS input: Btu/hr <br /> (EXCEPT DIRECT VENT) <br /> Combustion Air Opening Area(CAOA): A�.�� <br /> Total Btu/hr d!v!d ed by 3000 Btu/hr per in: CAOA= 40000 /3000 Btu/hr per in:= � in: <br /> Step 8:Calculate Minimum CAOA. <br /> Minimum CAOA=CAOA muklplled by Rf Minimum GAOA= 13.33 x 0.79 = 10.49 in: <br /> Step 9:Calculate Combustion Air Opening Diameter(CAOD) <br /> CA00=1.13 m uftlpBed by the sq u ore 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 deslred,ACH can be dete�mined using ASHRAE calculation or blower door test.Follow procedures in Sedion <br /> G304. <br />