Minn. R. agency 151, ch. 1346, ch. 8, pt. 1346.6012
IFGC Appendix E, Worksheet E-1
Residential Combustion Air Calculation Method
(for Furnace, Boiler, and/or Water Heater in the Same Space)
Step 1: Complete vented combustion appliance information.
Furnace/Boiler:
| _____ | Draft Hood | _____ | Fan Assisted | _____ | Direct Vent | Input: |
| (Not fan assisted) | & Power Vent | _____ Btu/hr | ||||
| Water Heater: | ||||||
| _____ | Draft Hood | _____ | Fan Assisted | _____ | Direct Vent | Input: |
| (Not fan assisted) | & Power Vent | _____ Btu/hr | ||||
Step 2: Calculate the volume of the Combustion Appliance Space (CAS) containing combustion appliances.
| The CAS includes all spaces connected to one another by code compliant openings. | CAS volume:_______ft3 |
Step 3: Determine Air Changes per Hour (ACH)1
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 method 4a (Standard Method).
Step 4: Determine Required Volume for Combustion Air.
| Total Btu/hr input of all combustion appliances (DO NOT COUNT DIRECT VENT APPLIANCES) | Input:_____Btu/hr |
| Use Standard Method column in Table E-1 to find Total Required Volume (TRV) | TRV:_____ft3 |
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.
| Total Btu/hr input of all fan-assisted and power vent appliances (DO NOT COUNT DIRECT VENT APPLIANCES) | Input:_____ Btu/hr |
| Use Fan-Assisted Appliances column in Table E-1 to find Required Volume Fan Assisted (RVFA) | RVFA:_____ ft3 |
| Total Btu/hr input of all non-fan-assisted appliances | Input:_____ Btu/hr |
| Use Non-Fan-Assisted Appliances column in Table E-1 to find Required Volume Non-Fan-Assisted (RVNFA) | RVNFA:_____ ft3 |
| Total Required Volume (TRV) = RVFA + RVNFA | |
| RV = _____ + _____ = _____ ft3 |
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.
Step 5: Calculate the ratio of available interior volume to the total required volume.
| Ratio = CAS Volume (from Step 2) divided by TRV (from Step 4a or Step 4b) | Ratio = _____ / _____ = _____ |
Step 6: Calculate Reduction Factor (RF).
| RF = 1 minus Ratio | RF = 1 - _____ = _____ |
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 (EXCEPT DIRECT VENT) | Input:_____ Btu/hr |
| Combustion Air Opening Area (CAOA): |
| Total Btu/hr divided by 3000Btu/hr per in2 |
| CAOA = _____/3000 Btu/hr per in2 = _____ in2 |
Step 8: Calculate Minimum CAOA.
| Minimum CAOA = CAOA multiplied by RF |
| Minimum CAOA = _____ x _____ = _____ in2 |
Step 9: Calculate Combustion Air Opening Diameter (CAOD)
| CAOD = 1.13 multiplied by the square root of Minimum CAOA |
| CAOD = 1.13 Minimum CAOA = _____ in |
1If desired, ACH can be determined using ASHRAE calculation or blower door test. Follow procedures in Section G304.
Minn. R. agency 151, ch. 1346, ch. 8, pt. 1346.6012
Statutory Authority: MS s 326B.101; 326B.106; 326B.13