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• <br /> • <br /> Directions-The Minnesota Fuel Gas Code method to calculate to size of a required combustion air opening,is coiled 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 /> Draft Hood _Fan Assisted /\Direct VentInput Btu/hr <br /> or Power Vent 046a{11/ <br /> 6 J / �� o <br /> Water Heater: • 1. v rim <br /> • <br /> __Draft Hood Fan Assisted Direct Vent Input Btu/hr f ; <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 openings. CAS volume: ft3 <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 VENTAPPUANCES) <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 than 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: Btu/hr <br /> Use Fan-Assisted Appliances column in Table E-1 to find RVFA: ft3 <br /> Required Volume Fan Assisted(RVFA) <br /> Total Btu/hr input of all Natural 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 TRV= + TRV ft3 <br /> If CAS Volume(from Step 2)is greater than TRY then no outdoor openings are needed. <br /> If CAS Volume(from Step 2)is less than TRV then go to STEP S. <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 /> Ratio= <br /> Step 6:Calculate Reduction Factor(RF). <br /> RF=1 minus Ratio RF=1- _ <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 Btu/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 in2= in2 <br /> Step 8:Calculate Minimum CAOA. <br /> Minimum CADA=CADA multiplied by RF Minimum CADA= x = in2 <br /> Step 9:Calculate Combustion Air Opening Diameter(CAOD) <br /> CAOD=1.13 multiplied by the square root of Minimum CAOA CAOD=1.13 Al 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 /> • <br /> Page 5 of 6 <br />