TOTAL INPUT OF APPLIANCES1,
THOUSANDS OF Btu/hr
(kW)
REQUIRED FREE AREA OF AIR-SUPPLY
OPENING OR DUCT, SQUARE INCHES
(sq mm)
ACCEPTABLE APPROXIMATE ROUND DUCT
EQUIVALENT DIAMETER2,
INCH (mm)
25 (8) 7 (4,500) 3 (75)
50 (15) 7 (4,500) 3 (75)
75(23) 11 (7,000) 4 (100)
100 (30) 14 (9,000) 4 (100)
125 (37) 18 (12,000) 5 (125)
150 (45) 22 (14,000) 5 (125)
175 (53) 25 (16,000) 6 (150)
200 (60) 29 (19,000) 6 (150)
225 (68) 32 (21,000) 6 (150)
250 (75) 36 (23,000) 7 (175)
275 (83) 40 (26,000) 7 (175)
300 (90) 43 (28,000) 7 (175)
325 (98) 47 (30,000) 8 (200)
350 (105) 50 (32,000) 8 (200)
375 (113) 54 (35,000) 8 (200)
400 (120) 58 (37,000) 9 (225)
1. For total inputs falling between listed capacities, use next largest listed input.
2. If flexible duct is used, increase the duct diameter by one inch. *
*Flexible duct shall be stretched with minimal sags.
TABLE 304.1
COMBUSTION AIR REQUIREMENTS FOR GAS-FIRED
APPLIANCES WHEN THE COMBINED INPUT IS UP TO
AND INCLUDING 400,000 Btu/hr
BTU Amount for Non-direct vent appliances_____________________
1 2 3 4 5
6 2
Conditioned space1 (in sq. ft.)
Total/
Continuous
Total/
Continuous
Total/
Continuous
Total/
Continuous
1000-1500 60/40 75/40 90/45 105/53 120/60 135/68
1501-2000 70/40 85/43 100/50 115/58 130/65 145/73
2001-2500 80/40 95/48 110/55 125/63 140/70 155/78
2501-3000 90/45 105/53 120/60 135/68 150/75 165/83
3001-3500 100/50 115/58 130/65 145/73 160/80 175/88
3501-4000 110/55 125/63 140/70 155/78 170/85 185/93
4001-4500 120/60 135/68 150/75 165/83 180/90 195/98
4501-5000 130-65 145/73 160/80 175/88 190/95 205/103
5001-5500 140/70 155/78 170/85 185/93 200/100 215/108
5501-6000 2
150/75 165/83 180/90 195/98 210/105 225/113
1. Conditioned space includes the basement and conditioned crawl spaces.
2. If conditioned space exceeds 6000 sq. ft. or there are more than 6 bedrooms, use Equation R403.5.2
R403.5.2 Total Ventilation rate.
The mechanical ventilation system shall rovide sufficient outdoor air to equal the total ventilation rate average
for each 1- hour period in accordance with Table R403.5.2, or Equation 403.5.2, based on the number of bedrooms and
square footage of conditioned space, including the basement and conditioned crawl spaces.
For the purposes of Table R403.5.2 and Section R403.5.3, the following applies:
a. Equation R403.5.2 Total ventilation rate:
Total ventilation rate (cfm) = (0.02 x square feet of conditioned space) + (15 x (number of bedrooms +1))
b. Equation R403.5.2.1 Continuous ventilation rate: Continuous ventilation rate (cfm) = Total ventiation rate/2
Amount Total _________________________
Amount Continuous____________________
TABLE R403.5.2
NUMBER OF BEDROOMS
VENTILATION REQUIREMENTS
ONE OR MULTIPLE POWER VENT
OR DIRECT VENT APPLIANCES OR
NO COMBUSTION APPLIANCESA
ONE OR MULTIPLE FAN-
ASSISTED APPLIANCES AND
POWER VENT OR DIRECT
VENT APPLIANCESB
ONE ATMOSPHERICALLY
VENTED GAS OR OIL
APPLIANE OR ONE
SOLID FUEL APPLIANCEC
MULTIPLE APPLIANCES THAT
ARE ATMOSPHERICALLY
VENTED GAS OR OIL
APPLIANCES OR SOLID FUEL
APPLIANCESD
1. Use the Appropriate Column to Estimate House Infiltration
a) pressure factor
(cfm/sf)
b) conditioned floor
area (sf)
(including unfinished basements)
Estimated House
Infiltration (cfm):
[1a x 1b]
2. Exhaust Capacity
a) clothes dryer
b) 80% of largest
exhaust rating (cfm):
(not applicable if recirculating system or if powered makeup air is electrically interlocked and matched to exhaust)
c) 80% of next largest
exhaust rating (cfm):
not applicable
(not applicable if recirculating system or if powered makeup air is electrically interlocked and matched to exhaust)
Total Exhaust Capacity
(cfm):
[2a+2b+2c]
3. Makeup Air Requirement
a) Total Exhaust
Capacity
(from above)
b) Estimated House
Infiltration (from
above)
Makeup Air
Quality (cfm):
[3a - 3b]
(if value is negative, no makeup air is needed
4. For Makeup Air Opening Sizing, refer to Table 501.4.2.
A. Use this column if there are other than fan-assisted or atmospherically vented gas or oil appliances or if there are no combustion appliances.
B. Use this column if there is one fan-assisted appliance per venting system. Other than atmospherically vented appliances may also be included.
C. Use this column if there is one atmospherically vented (other than fan-assisted) gas or oil appliance per venting system or one solid fuel appliance.
D. Use this column if there are multiple atmospherically vented gas or oil appliances using a common vent or if there are atmospherically
vented gas or oil appliances and solid fuel appliances.
Table 501.4.1
Procedure to Determine Makeup Air Quantity for Exhaust Appliances in Dwelling Units
Choose Which Applies
0.15
0.00
135.00
135.00
135.00
0.00
135.00
0.09
0.00
135.00
135.00
135.00
0.00
135.00
0.06
0.00
135.00
135.00
135.00
0.00
135.00
0.03
0.00
135.00
135.00
135.00
0.00
135.00
TYPE OF OPENING
ONE OR MULTIPLE POWER
VENT OR DIRECT VENT
APPLIANCES OR NO
COMBUSTION
APPLIANCESA
ONE OR MULTIPLE FAN-
ASSISTED APPLIANCES
AND POWER VENT OR
DIRECT VENT APPLIANCESB
ONE
ATMOSPHERICALLY
VENTED GAS OR OIL
APPLIANCE OR ONE
SOLID FUEL
APPLIANCEC
MULTIPLE APPLIANCES
THAT ARE
ATMOSPHERICALLY
VENTED GAS OR OIL
APPLIANCES OR SOLID
FUEL APPLIANCESD
PASSIVE MAKEUP
AIR OPENING
DUCT
DIAMETERE,F,G
OR SYSTEM (cfm) (cfm) (cfm) (cfm) (inches)
Passive opening 1-36 1-22 1-15 1-9 3
Passive opening 37-66 23-41 16-28 10-17 4
Passive opening 67-109 42-66 29-46 18-28 5
Passive opening 110-163 67-100 47-69 29-42 6
Passive opening 164-232 101-143 70-99 43-61 7
Passive opening 233-317 144-195 100-135 62-83 8
Passive opening
with motorized
damper
318-419 196-258 136-179 84-110 9
Passive opening
with motorized
damper
420-539 259-332 180-230 111-142 10
Passive opening
with motorized
damper
540-679 333-419 231-290 143-179 11
Powered makeup
airH
>679 >419 >290 >179 Not applicable
A. Use this column if there are other than fan-assisted or atmospherically vented gas or oil appliances or if there are no combustion appliances.
B. Use this column if there is one fan-assisted appliance per venting system. Other than atmospherically vented appliances may also be included.
C. Use this column if there is one atmospherically vented (ther than fan-assisted) gas or oil appliance per venting system or one solid fuel appliance.
D. Use this column if there are multiple atmospherically vented gas or oil appliances using a common vent or if there are atmospherically vented
gas or oil appliances and solid fuel appliances.
E. An equivalent length of 100 feet of round smooth metal duct is assumed. Subtract 40 feet for the exterior hood and ten feet for each 90-degree
elbow to determine the remaining length of straight duct allowable.
F. If flexible duct is used, increase the duct diameter by one inch. Flexible duct shall be stretched with minimal sags.
G. Barometric dampers are prohibited in passive makeup air openings when any atmospherically vented appliance is installed.
H. Powered makeup air shall be electrically interlocked with the largest exhaust system.
Table 501.4.2
Makeup Air Opening Sizing Table for New and Existing Dwelling Units
Residential Combustion Air Calculation Method
(for Furnace, Boiler, and/or Water Heater in the Same Space)
Complete vented combution appliace information:
Furnace/Boiler:
Draft Hood Fan Assisted Direct Vent Input: Btu/hr
(Not fan Assisted) & Power Vent
Water Heater:
Draft Hood Fan Assisted Direct Vent Input: Btu/hr
( Not fan Assisted) & Power Vent
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: ft
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).
Determine Required Volume for Combustion Air.
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) TRV then no outdoor openings are needed.
If CAS Volume (from Step 2) TRV then go to
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 TRV = + = ft
3
If CAS Volume (from Step 2) TRV then no outdoor openings are needed.
If CAS Volume (from Step 2) TRV then go to
Calculate the ratio of available interior volume to the total required volume.
Ratio = CAS Volume (from Step 2) TRV (from Step 4a or Step 4b) Ratio =
Calculate Reduction Factor (RF).
RF = 1 Ratio RF = - =
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 by 3000 Btu/hr per in
2
/ Btu/hr per in
2
= in
2
Calculate Minimum CAOA.
Minimum CAOA = CAOA RF Minimum CAOA = x = in
2
Calculate Combustion Air Opening Diameter (CAOD)
CAOD = 1.13 Minimum CAOA CAOD = 1.13 x Minimum CAOA = in
1
If desired, ACH can be determined using ASHRAE calculation or blower door test. Follow procedures in Section 304.
CAOA =
1
0.00
1.00
0
1
0.00
0
0
0
0
3,000
0.00
0.00
1.00
0.00
Residential Combustion Air Required Volume (Required Interior Volume Based on Input Rating of Appliances)
Known Air Infiltration Rate (KAIR) Method (ft
3
)
Input Rating Standard Method Fan Assisted Non-Fan-Assisted
(Btu/hr) (ft
3
) 1994
1
to Present Pre 1994
2
1994
1
to Present Pre 1994
2
5,000 250 375
188
525 263
10,000 500 750
375
1,050 525
15,000 750 1,125
563
1,575 788
20,000 1,000 1,500
750
2,100 1,050
25,000 1,250 1,875
938
2,625 1,313
30,000 1,500 2,250
1,125
3,150 1,575
35,000 1,750 2,625
1,313
3,675 1,838
40,000 2,000 3,000
1,500
4,200 2,100
45,000 2,250 3,375
1,688
4,725 2,363
50,000 2,500 3,750
1,875
5,250 2,625
55,000 2,750 4,125
2,063
5,775 2,888
60,000 3,000 4,500
2,250
6,300 3,150
65,000 3,250 4,875
2,438
6,825 3,413
70,000 3,500 5,250
2,625
7,350 3,675
75,000 3,750 5,625
2,813
7,875 3,938
80,000 4,000 6,000
3,000
8,400 4,200
85,000 4,250 6,375
3,188
8,925 4,463
90,000 4,500 6,750
3,375
9,450 4,725
95,000 4,750 7,125
3,563
9,975 4,988
100,000 5,000 7,500
3,750
10,500 5,250
105,000 5,250 7,875
3,938
11,025 5,513
110,000 5,500 8,250
4,125
11,550 5,775
115,000 5,750 8,625
4,313
12,075 6,038
120,000 6,000 9,000
4,500
12,600 6,300
125,000 6,250 9,375
4,688
13,125 6,563
130,000 6,500 9,750
4,875
13,650 6,825
135,000 6,750 10,125
5,063
14,175 7,088
140,000 7,000 10,500
5,250
14,700 7,350
145,000 7,250 10,875
5,438
15,225 7,613
150,000 7,500 11,250
5,625
15,750 7,875
155,000 7,750 11,625
5,813
16,275 8,138
160,000 8,000 12,000
6,000
16,800 8,400
165,000 8,250 12,375
6,188
17,325 8,663
170,000 8,500 12,750
6,375
17,850 8,925
175,000 8,750 13,125
6,563
18,375 9,188
180,000 9,000 13,500
6,750
18,900 9,450
185,000 9,250 13,875
6,938
19,425 9,713
190,000 9,500 14,250
7,125
19,950 9,975
195,000 9,750 14,625
7,313
20,475 10,238
200,000 10,000 15,000
7,500
21,000 10,500
205,000 10,250 15,375
7,688
21,525 10,763
210,000 10,500 15,750
7,875
22,050 11,025
215,000 10,750 16,125
8,063
22,575 11,288
220,000 11,000 16,500
8,250
23,100 11,550
225,000 11,250 16,857
8,438
23,625 11,813
230,000 11,500 17,250
8,625
24,150 12,075
1
The 1994 date refers to dwellings constructed under the 1994 Minnesota Energy Code. The default KAIR used in this section of the table is 0.20 ACH.
2
This section of the table is to be used for dwellings constructed prior to 1994. The default KAIR used in this section of the table is 0.40 ACH.
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