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Directions-The Minnesota Fuel Gas Code method to calculate fo 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 ouf. <br /> IFGC A endix E,Worksheet E-1--Residential Combustion Air Calculation Method for Furnace, Boiler,and/or Water Heater in the Same S ace <br /> Step 1:Complete vented combustion appliance information. <br /> Furnace/Boiler: <br /> �raft Hood OFan Assisted QDirect Vent Input: 80000 Btu/hr <br /> or Power Vent <br /> Water Heater: <br /> �raft Hood Q Fan Assisted �irect Vent Input: 55000 Btu/hr <br /> or Power Vent <br /> Step 2:Caiculate the volume of the Combustion Appliance Space(CAS)containing combustion appliances.The CAS includes all <br /> spaces connected to one another by code compliant openings. <br /> CAS volume: �280 ft' L x W x H L W H <br /> Step 3: Determine Air Changes per Hour(ACH)1 <br /> Default ACH values have been incorporated into Tabie 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 /> ------------- <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(TR�If CAS Volume(from Step 2)is greater than TRV then no outdoor openings are needed.If CAS Volume(from Step 2)is less than <br /> TRV then go to STEP 5. <br /> 4b.Known Air Infiltration Rate(KAIR)Method(DO NOT COUNT DIRECT VENT APPLIANCES) <br /> Totai Btu/hr input of ail fan-assisted and power vent appliances Input: 55000 Btu/hr <br /> Use Fan-Assisted Appliances column in Table E-1 to find RVFA: 4125 ft3 <br /> Required Voiume 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: ft' <br /> Required Volume Natural draft appliances(RVNDA) <br /> Total Required Volume(TR�=RVFA+RVNDA rRv= 4125 + ----------- = 4125 TRV ft' <br /> If CAS Volume(from Step 2)is greater than TRV then no outdoor openings are needed.If CAS Volume(from Step 2)is/ess than TRV then go to STEP 5. <br /> Step 5:Calculate the ratio of available interior voiume to the total required volume. <br /> Ratio=CAS Volume(from Step 2)divided byTRV(from Step 4a or Step 4b) <br /> Ratio=1280 �4125 _.31 <br /> Step 6:Calculate Reduction Factor(RF). RF=1 minus Ratio <br /> RF=� - •31 _.69 <br /> Step 7:Caiculate singie outdoor opening as if all combustion air is from outside.Total Btu/hr input of all Combustion Appliances in the same CAS <br /> �nput: 55000 Btu/hr(EXCEPT DIRECT VENT) <br /> Combustion Air Opening Area(CAOA):Total Btu/hr divided by 3000 Btu/hr per in2 <br /> caoa=55000 /3000 Btu/hr per inz=�8•3 inZ <br /> Step 8:Calculate Minimum CAOA: Minimum CAOA=CAOA multiplied by RF <br /> Minimum CAOA=�H.3 X.69 _12.6 inZ <br /> Step 9:Calculate Combustion Air Opening Diameter(CAOD): CAOD=1.13 multiplied by the square root of Minimum CAOA <br /> CAOD= 1.13� Minimum CAOA= 4'0 in.diameter 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 G304. <br /> 5 <br />