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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/Boiler: <br /> �Ls <br /> _ <br /> Draft Hood _ Fan Assisted Direct Vent Input: gtu/hr <br /> or Power Vent <br /> Water Heater: ,..- <br /> _Draft Hood Fan Assisted _Direct Vent Input: Btu/hr <br /> 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 07e CAS volume: �ZvG hs <br /> l x W x H t t>11✓�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). <br /> if the year of construction or ACH is not known,use 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: ft' <br /> Volume(TRV) <br /> If CAS Volume(from Step 2)Is greater than TRV then no outdoor openings are needed. <br /> If CAS Volume(from Step 2)is less than TRV then to to STEP S. <br /> 4b.Known Air Infiltration Rale(KAIR)Method(DO NOT COUNT DIRECT VENT APPtIAN �/L�� <br /> Total Btu/hr input of all fan-assisted and power vent appliances Input: / to/hr <br /> Use Fan-Assisted Appliances column in Table E-1 to find RVFA: -7 V•Z�fts <br /> Required Volume Fan Assisted(RVFA) <br /> Total Btu/hr input of all Natural draft appliances Input: f� Btu/hr <br /> Use Natural draft Appliances column in Table E-1 to find RVNFA: /v. _ - - ft' <br /> Required Volume Natural draft appliances(RVNOA) <br /> Total Required Volume(TRV)=RVFA+RVNOA TRV: - _TRV ft' <br /> If CAS Volume(from Step 2)is greater than TRV then no outdoor openings are needed. <br /> If CAS Volume(from Step 2)is less than TRV then-go to STEP S. <br /> Step S:Calculate the ratio of available interior volume to the total required volume. <br /> Ratio-CAS Volume(from Step 2)divided by TRV(from Step 4a or Step 4b) L <br /> Ratio <br /> Step 6:Calculate Reduction Factor(RF). <br /> RF=1 minus Ratio RF.= - <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: �e-�tu/hr <br /> (EXCEPT DIRECT VENT) <br /> Combustion Air Opening Area(CAOA): <br /> Total Btu/hr divided by 3000 Btu/hr per in' CAOA= /3000 Btu/hr per in'= 2-5 (n' <br /> Step 8:Calculate Minimum CAOA. <br /> Minimum CAOA=CAOA multiplied by RF Minimum CAOA <br /> Step 9:Calculate Combustion Air Opening Diameter(CAOD) <br /> CAOD=1.13 multiplied by the square root of Minimum CAOA CAOD=1.13 V Minimum CAOA=J�Kn.diameter <br /> o up one inch in size if using flex duct TT�� <br /> 1 If desired,ACH can be determined using ASHRAE calculation or blower door test.Follow procedures in Section <br /> G304. <br /> Page 5 of 6 <br />