Laserfiche WebLink
• <br /> Directions-The Minnesota Fuel Gas Codeethod to calculate to size of a required combustion air opening, is called the Known Air <br /> Infiltration Rate Method. For new constru4tion,4b of step 4 is required to be filled out. <br /> IFGC Appendix E,Worksheet E-1—Residential l ombustion Air Calculation Method(for Fumace,Boiler,and/or Water Heater in the Same Space) <br /> Step 1:Complete vented combustion appliance information. <br /> Furnace/Boiler: <br /> raft Hood OFan Assisted �irect Vent Input: 120,000 Btu/hr <br /> or Power Vent <br /> Water Heater: <br /> IDDraft Hood ✓( ]Fan Assisted Direct Vent Input: 75,000 Btu/hr <br /> or Power Vent <br /> Step 2:Calculate the volume of the Combustion Appliance Space(CAS)containing combustion appliances.The CAS indudes all <br /> spaces connected to one another by code compliant openings. <br /> CAS volume: 2160 ft3 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 Table E-1 for use with Method 4b(KAIR Method). <br /> If the year of construction or ACH is not known,ruse method 4a(Standard Method). <br /> Step 4:Determine Required Volume for Combuslon 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)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(DOI NOT COUNT DIRECT VENT APPLIANCES) <br /> Total Btu/hr input of all fan-assisted and power vnt appliances Input: 75000 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 Natural draft appliances Input: 0 Btu/hr <br /> Use Natural draft Appliances column in Table E-1 to find RVNFA: 0 ft3 <br /> Required Volume Natural draft appliances(RVNDA) <br /> Total Required Volume(TRV)=RVFA+RVNDA TRV= 5625 + 0 = 5625 TRV ft3 <br /> 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 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 /> Ratio=2160 /5625 =.38 <br /> Step 6:Calculate Reduction Factor(RF). RF=1 minus Ratio <br /> RF=1- .38 =.62 <br /> Step 7:Calculate single outdoor opening as if all combustion air is from outside.Total Btu/hr input of all Combustion Appliances in the same CAS <br /> Input: 75000 Btu/hr(EXCEPT DIRECT VENT) <br /> Combustion Air Opening Area(CAOA):Total Btu/hr divided by 3000 Btu/hr per in2 <br /> CAOA=75000 /3000 Btu/hr per in'F 25 in2 <br /> Step 8:Calculate Minimum CAOA: Minimum CAOA=CAOA multiplied by RF <br /> Minimum CAOA=25 x.62 =15.5 in2 <br /> Step 9:Calculate Combustion Air Opening Diameter kCAOD): CAOD=1.13 multiplied by the square root of Minimum CAOA <br /> CAOD=1.13 NI Minimum CAOA= 5" rigid 6"fllx 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 />