CODES

ADOPTS WITH AMENDMENTS:

International Fuel Gas Code 2012 (IFGC 2012)

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
(Not fan assisted)
__________ Fan Assisted
& Power Vent
__________ Direct VentInput: __________ Btu/hr
Water Heater:
__________ Draft Hood
(Not fan assisted)
__________ Fan Assisted
& Power Vent
__________ Direct VentInput: __________ 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.
4a. Standard Method.
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.
4b. Known Air Infiltration Rate (KAIR) Method.
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 of all Non-Fan-Assisted AppliancesInput: __________ 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 + RVNFARV = __________ + __________ = __________ 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.

(continued)

WORKSHEET E-1—(continued)

Residential Combustion Air Calculation Method
(for Furnace, Boiler, and/or Water Heater in the Same Space)

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 RatioRF = 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 3000 Btu/hr per in2CAOA = __________ / 3000 Btu/hr per in2 = __________ in2
Step 8: Calculate Minimum CAOA.
Minimum CAOA = CAOA multiplied by RFMinimum CAOA = __________× __________ = __________ in2
Step 9: Calculate Combustion Air Opening Diameter (CAOD).
CAOD = 1.13 multiplied by the square root of Minimum CAOACAOD = 1.13 Minimum CAOA = __________ in
1If desired, ACH can be determined using ASHRAE calculation or blower door test. Follow procedures in Section G304.
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