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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: 8000 <br />raft Hood Dan Assisted ✓ krect Vent Input: Btu/hr or Power Vent <br />Water Heater:40000 <br />raft Hood a 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. <br />640 <br />The CAS includes all spaces connected to one another by code compliant openings. CAS volume: ft3 <br />LxWxH 10 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). 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: 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: 40000 Btu/hr <br />Use Fan -Assisted Appliances column in Table E-1 to find RVFA: 3000 ft, <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 = 3000 _+0 __3000 TRV ft <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 =640 / 3000 = 0.21 <br />Step 6: Calculate Reduction Factor (RF). <br />RF=1min us Ratio RF=1- 0.21 -0.79 <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): 1 3.33 <br />Total Btu/hr di vid ed by 3000 Btu/hr per int CAOA = 40000 / 3000 Btu/hr per int= int <br />Step 8: Calculate Minimum CAOA. <br />Minimum CAOA = CAOA multiplied by RF Minimum CAOA = 13.33 x 0.79 = 10.49 int <br />Step 9: Calculate Combustion Air Opening Diameter (CAOD) <br />CAOD = 1.13 multiplied by the square root of Minimum CAOA CAOD = 1.13V Minimum CAOA = 4.12 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 />