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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,46 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 /> Draft Hood _ Fan Assisted Direct Vent Input: Btu/hr <br /> or Power Vent <br /> Water Heater. 75,000 <br /> _Draft Hood Fan Assisted _Direct Vent Inpu Btu/hr <br /> or Power Vent <br /> Step 2:Calculate the volume of the Combustion Appiiance Space(CAS)containing combustion appiiances. <br /> The CAS includes all spaces connected to one another by code compliant openings. CAS volume: 1038 3 <br /> LxWxH L 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►. <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: ft3 <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 thon TRV then go to STEP 5. <br /> 4b.Known Air Infiltration Rate(KAIR)Method(DO NOT COUNT DIRECT VENT APPL <br /> Totai Btu/hr input of all fan-assisted and power vent appliances Input: 75,000 Btu/hr <br /> Use Fan-Assisted Appliances column in Table E-1 to find RVFA:5625 ft3 <br /> Required Volume Fan Assisted(RVFA) <br /> Total Btu/hr input of all Naturel draft appliances 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 Required Volume(TRV)=RVFA+RVNDA rRv= 5625 + � _ 5625 TRV ft3 <br /> If CAS Volume(from Step 2►is greater thon TRV then no outdoor openings are needed. <br /> If CAS Volume(from Step 2)is less than TRV then go to STEP 5. <br /> Step 5: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) <br /> rtatio= 1038 � 5625 - '�8 <br /> Step 6:Calculate Redudion Factor(RF). <br /> RF=1 minus Ratio RF=1- ��$ _ .82 <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: 75,000 Btu/hr <br /> (EXCEPT DIRECT VENT) <br /> Combustion Air Opening Area(CAOA�: <br /> Total Btu/hr divided by 3000 Btu/hr per in' CAOA 75,000 /3000 Btu/hr per inZ= 25 inZ <br /> Step 8:Calculate Minimum CAOA. <br /> Minimum CAOA=CAOA multiplied by RF Minimum CAOA= 25 x .$2 = 20.5 ��z <br /> Step 9:Calculate Combustion Air Opening Diameter(CAOD) <br /> CAOD=1.13 multiplied by the square root of Minimum CAOA CAOD=1.13� Minimum CAOA=�in.diameter <br /> go up one inch in size 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 /> � <br />