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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: 1 00000 <br />raft Hood Dan Assisted ✓ krect Vent Input: Btu/hr or Power Vent <br />Water Heater: <br />40000 <br />raft Hood Ft—/]Fan Assisted Direct Vent Input: Btu/hr or Power Vent <br />Step 2: Calculate the volume of the Combustion Appliance Space (CAS) containing combustion appliances. 1 344 <br />The CAS includes all spaces connected to one another by code compliant openings. CAS volume: 113 <br />LXWxH = L8�W LjH <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). If the year of construction or ACH is not known, use <br />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 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: 400000 Btu/hr <br />Use Fan -Assisted Appliances column in Table E-1 to find RVFA: 3000 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 % <br />Required Volume Natural draft appliances (RVNDA) <br />Total Required Volume TRV = RVFA+ RVNDA TRV = 3000 + 0 - 3000 TRV k3 <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 = 1344 / 3000 = 0.45 <br />Step 6: Calculate Reduction Factor (RF). d <br />RF=Imin us Ratio RF=1- 0.45 -0.55 <br />Step 7: Calculate single outdoor opening as if all combustion air is from outside. 40000 <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): Q Q`j <br />Total Btu/hr divided by 3000Bto/hr perin2 CAOA= ` A +0000 /3000 Btu/hr per in -13.33 inz <br />Step 8: Calculate Minimum CAOA. G <br />Minimum CAOA=CAOAmultiplied by RF Minimum CAOA = 13.33 x 0.55 = 7.36 in - <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 = 3.07 in. diameter go up one inch in size <br />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 />