Published: 2015

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1346.6012 IFGC APPENDIX E, WORKSHEET E-1.

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.

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:

_

ft

3

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:

_

ft

3

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:

_

ft

3

Total Required Volume (TRV) = RVFA + RVNFA

RV =

_

+

_

=

_

ft

3

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 3000 Btu/hr per in2

CAOA =

_

/3000 Btu/hr per in

2

=

_

in

2

Step 8: Calculate Minimum CAOA.

Minimum CAOA = CAOA multiplied by RF

Minimum CAOA =

_

x

_

=

_

in

2

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.

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.

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:

_

ft

3

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:

_

ft

3

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:

_

ft

3

Total Required Volume (TRV) = RVFA + RVNFA

RV =

_

+

_

=

_

ft

3

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 3000 Btu/hr per in2

CAOA =

_

/3000 Btu/hr per in

2

=

_

in

2

Step 8: Calculate Minimum CAOA.

Minimum CAOA = CAOA multiplied by RF

Minimum CAOA =

_

x

_

=

_

in

2

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.