Current through Register Vol. 49, No. 13, September 23, 2024
N1104.1
Mechanical
ventilation requirements. A mechanical ventilation system shall be
installed that meets the requirements of this section. This section covers the
continuous and total mechanical ventilation requirements for dwelling unit
ventilation at summer and winter climatic design conditions according to
Section N1104.4.13 and chapter 1346. All unfinished basements, crawlspaces, and
levels shall be provided with a minimum ventilation rate of 0.02 cfm per square
foot, or a minimum of one supply duct and one return duct. The supply and
return ducts shall be separated by one-half the diagonal dimension of the
basement to avoid a short circuit of the air circulation.
Exception: Kitchen and bath fans that are not
included as part of the mechanical ventilation system are exempt from the
requirements of Section N1104 but shall comply with the IRC.
N1104.1.1
Additions or alterations to
existing buildings. Additions or alterations to existing buildings shall
require a dwelling unit mechanical ventilation system that meets Section N1104.
Exception: Buildings whose permit of initial
construction was applied for prior to April 15, 2000, and did not require a
dwelling unit mechanical ventilation system.
N1104.2
Total ventilation rate.
The mechanical ventilation system shall provide sufficient outdoor air to equal
the total ventilation rate average, for each one-hour period according to Table
N1104.2, or Equation 11-1, based on the number of bedrooms and the square
footage of conditioned space, including the basement but excluding conditioned
crawl spaces. For heat recovery ventilators and energy recovery ventilators the
average hourly ventilation capacity must be determined in consideration of any
reduction of exhaust or outdoor air intake, or both, for defrost or other
equipment cycling per HVI Standard 920.
| Equation 11-1: |
| Total ventilation rate (cfm) |
= |
(0.02 x square feet of conditioned space) + [15 x (number
of bedrooms + 1)] |
N1104.2.1
Continuous ventilation. A minimum of 50 percent of the total ventilation
rate, but not less than 40 cfm, shall be provided, on a continuous rate average
for each one-hour period according to Table N1104.2 or Equation 11-2. The
portion of the mechanical ventilation system that is intended to be continuous
may have automatic cycling controls providing the average flow rate for each
hour meeting the requirements of Section N1104.2.1.
| Equation 11-2: |
| Continuous ventilation (cfm) |
= |
total ventilation rate/2 |
N1104.2.1.1
Ventilation rate. The continuous ventilation system shall be
balanced in accordance with Section N1104.4.2.
Exception: If the local ventilation requirements
according to IRC Section R303.3 are being met by the continuous ventilation
system, it shall be capable of operating at a rate not more than 100 percent
greater than required by Section N1104.2.1.
N1104.2.2
Intermittent
ventilation. The difference between the total ventilation rate and the
continuous ventilation rate shall be based on flow rates as designed or as
installed.
| Table N1104.2 |
| Total and Continuous Ventilation Rates (in
cfm) |
|
Number of Bedrooms |
|
1 |
2 |
3 |
4 |
5 |
6 ² |
| Conditioned space1 (in sq.
ft.) |
Total/ Continuous |
Total/ Continuous |
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.
2 If conditioned space exceeds 6000 sq.
ft. or there are more than 6 bedrooms, use Equation 11-1 from Section N1104.2
to calculate total ventilation rate.
N1104.3
Ventilation system
requirements. The mechanical ventilation system shall be one of three
types: exhaust according to Section N1104.3.1; balanced, and HRV/ERV according
to Section N1104.3.2; or other method according to Section N1104.3.3.
N1104.3.1
Exhaust systems. Fans
used to comply with the continuous ventilation part of the mechanical
ventilation system shall:
1. meet the minimum
continuous ventilation rate in Section N1104.2.1 at the point of
discharge;
2. be designed and
certified by the equipment manufacturer as capable of continuous operation at
the rated cfm;
3. have a maximum
1.0 sone per HVI Standard 915 for surface mounted fans;
4. be permitted to use a required overcurrent
protection device as a disconnect per the National Electric Code, incorporated
by reference in Minnesota Rules, chapter 1315; and
5. comply with the Minnesota Mechanical Code,
chapter 1346, which may require additional make-up air.
Fans used to comply with the intermittent ventilation part of
the mechanical ventilation system shall have a maximum 2.5 sone per HVI
Standard 915.
N1104.3.2
Balanced, and HRV/ERV
systems. A heat recovery ventilator (HRV) or energy recovery ventilator
(ERV) shall meet either:
1. the requirements
of HVI Standard 920, 72 hours minus 13 degrees Fahrenheit cold weather test;
or
2. certified by a registered
professional engineer and installed per manufacturer's installation
instructions.
An HRV or ERV intended to comply with both the continuous and
total ventilation rate requirements shall meet the rated design capacity of the
continuous ventilation rate in Section N1104.2.1 under low capacity and meet
the total ventilation rate in Section N1104.2.2 under high capacity.
Exception: The balanced, and HRV/ERV system may
include exhaust fans to meet the intermittent ventilation rate. Surface mounted
fans shall have a maximum 2.5 sones per HVI Standard 915.
N1104.3.3
Other
methods. Any mechanical ventilation system consisting of exhaust fans,
supply fans, or a combination of both, complying with Section N1104, shall be
allowed. A mechanical ventilation system specifically identified in Section
N1104.3.1 or N1104.3.2 shall not conflict with Sections N1104.3.1 and
N1104.3.2. For the purposes of this section, the delivered ventilation rate is
the larger of the total air flow of the operating supply fans, or total air
flow of the operating exhaust fans.
N1104.4
Installation
requirements. All types of mechanical systems shall meet the
requirements of this section. The mechanical ventilation system and its
components shall also be installed according to the Mechanical Code, Minnesota
Rules, chapter 1346, and the equipment manufacturer's installation
instructions.
N1104.4.1
Air
distribution and circulation. Outdoor air shall be delivered to each
habitable space by a forced air circulation system, separate duct system,
individual inlets, or a passive opening.
N1104.4.1.1
Forced air circulation
systems. When outdoor air is supplied directly through a forced air
circulation system, the requirements of this section shall be met by either:
(a) when an outdoor air supply is not ducted
to the forced air system, controls shall be installed to allow the forced air
system to provide an average circulation flow rate each hour, of not less than
0.15 cfm per square foot of the conditioned floor area; or
(b) when the outdoor air supply is ducted to
the forced-air system, it shall be tempered so that the mixed air temperature
shall be no less than 60 degrees Fahrenheit or the heating equipment
manufacturer's installation instruction, and controls shall be installed to
allow the forced air circulation system to provide an average flow rate not
less than 0.075 cfm per square foot of conditioned floor area.
N1104.4.1.2
Directly ducted
and individual room inlets. When outdoor air is supplied directly to
habitable spaces with an airflow of 20 cfm or greater, the system shall be
designed and installed to temper incoming air to not less than 40 degrees
Fahrenheit measured at the point of distribution into the space.
| Table N1104.4.1.1(1) |
| Indirect Circulation Air Flow Rates for
Forced-Air Circulation Systems (in cfm) |
|
|
Forced-Air Circulation Systems Flow Rate
(cfm) |
|
|
600 |
800 |
1000 |
1200 |
1400 |
1600 |
1800 |
2000 |
| Conditioned Floor Area |
Average Air Flow each Hr (cfm) |
Number of Minutes per Hour, if cycled |
| 1000-1500 |
225 |
23 |
17 |
14 |
12 |
10 |
9 |
8 |
7 |
| 1501-2000 |
300 |
30 |
23 |
18 |
15 |
13 |
12 |
10 |
9 |
| 2001-2500 |
375 |
38 |
29 |
23 |
19 |
16 |
14 |
13 |
12 |
| 2501-3000 |
450 |
45 |
34 |
27 |
23 |
20 |
17 |
15 |
14 |
| 3001-3500 |
525 |
53 |
40 |
32 |
27 |
23 |
20 |
18 |
16 |
| 3501-4000 |
600 |
60 |
45 |
36 |
30 |
26 |
23 |
20 |
18 |
| 4001-4500 |
675 |
na1 |
51 |
41 |
34 |
29 |
26 |
23 |
21 |
| 4501-5000 |
750 |
na1 |
57 |
45 |
38 |
33 |
29 |
25 |
23 |
| 5001-5500 |
825 |
na1 |
na1 |
50 |
42 |
36 |
31 |
28 |
25 |
| 5501-6000 |
900 |
na1 |
na1 |
54 |
45 |
39 |
34 |
3 |
27 |
1 Not allowed
| Table N1104.4.1.1(2) |
| Direct Distribution Air Flow Rates Using
Forced-Air Circulation Systems (in cfm) |
|
|
Forced-Air Circulation Systems Flow Rate
(cfm) |
|
|
600 |
800 |
1000 |
1200 |
1400 |
1600 |
1800 |
2000 |
| Conditioned Floor Area |
Average Air Flow each Hr (cfm) |
Number of Minutes per Hour, if cycled |
| 1000-1500 |
115 |
13 |
9 |
7 |
6 |
5 |
5 |
4 |
4 |
| 1501-2000 |
150 |
15 |
13 |
9 |
8 |
7 |
6 |
5 |
5 |
| 2001-2500 |
190 |
19 |
15 |
13 |
10 |
8 |
7 |
7 |
6 |
| 2501-3000 |
225 |
23 |
17 |
14 |
13 |
10 |
9 |
8 |
7 |
| 3001-3500 |
265 |
27 |
20 |
15 |
14 |
13 |
10 |
9 |
8 |
| 3501-4000 |
300 |
30 |
23 |
18 |
15 |
13 |
13 |
10 |
9 |
| 4001-4500 |
340 |
34 |
26 |
21 |
17 |
15 |
13 |
13 |
11 |
| 4501-5000 |
375 |
38 |
24 |
23 |
19 |
17 |
15 |
13 |
13 |
| 5001-5500 |
415 |
42 |
32 |
25 |
21 |
18 |
16 |
14 |
13 |
| 5501-6000 |
450 |
45 |
34 |
27 |
23 |
20 |
17 |
15 |
14 |
N1104.4.1.3
Passive openings.
When outdoor air is brought in through a passive opening, the maximum cfm of
the outdoor air requirements shall be combined with the maximum makeup air
requirements of Minnesota Rules, chapter 1346. The combined air rates shall be
brought into the dwelling unit in accordance with chapter 1346. Controls shall
be installed to distribute air throughout the dwelling unit as required by
Section N1104.4.1.1a.
N1104.4.2
Airflow verification.
Mechanical ventilation system airflows greater than 30 cfm at the building
exhaust or intake shall be tested and verified using a flow hood, flow grid,
pitot tube, or other airflow measuring device. The airflow verification results
shall be made available to the building official upon request.
N1104.4.2.1
Airflow
requirements. When the system is intended to be unbalanced, the design
supply air flow shall not exceed 0.05 cfm per square foot of conditioned space.
The operating exhaust air flow shall meet the requirements of Section N1104.3.1
and the Minnesota Mechanical Code, chapter 1346, which may require additional
makeup air. When the system is intended to be balanced, the exhaust and supply
airflows shall be within plus or minus ten percent of each other or the
manufacturer's installation instructions, whichever is more
restrictive.
N1104.4.3
Fans. When used as part of the mechanical ventilation system,
fans shall be capable of delivering the designed air flow as determined by
Section N1104.2 according to HVI Standard 916. Fans shall be designed and
certified by the equipment manufacturer as capable of continuous operation at
the rated cfm. Surface mounted fans used to comply with the continuous
ventilation part of the mechanical ventilation system shall have a maximum 1.0
sone per HVI Standard 915. Fans used to comply with the intermittent
ventilation part of the mechanical ventilation system shall have a maximum 2.5
sone per HVI Standard 915.
Exception: Sone requirements do not apply to
forced air circulation systems and remotely mounted fans, provided the remotely
mounted fan is not in a habitable space and there is at least 4 feet of
ductwork between the fan and the grille.
N1104.4.4
Multifan systems.
When two or more exhaust fans in a dwelling unit share a common exhaust duct,
each fan shall be equipped with a backdraft damper to prevent recirculation of
exhaust air into another room.
N1104.4.5
Connection to forced air
circulation systems. Air ducts connected directly to the forced air
circulation system can be used to meet the mechanical ventilation system
requirements. Either the tempered outdoor air may be supplied to, or exhaust
air may be drawn from, the forced air circulation system, but not both.
Exception: Both outdoor air and exhaust air may
be connected to the forced air circulation system, provided that controls are
installed to ensure that the forced air circulation system is operating
whenever the mechanical ventilation system is operating or other means are
provided to prevent short circuiting of fresh air according to the
manufacturer's recommendations.
N1104.4.6
Dampers. Mechanical
ventilation system supply and exhaust ducts shall be provided with accessible
backflow dampers to minimize flow to or from the outdoors when the ventilation
system is off.
N1104.4.7
Intake openings. Exterior air intake openings shall be accessible for
inspection and maintenance. Intake openings shall be located in accordance with
the Minnesota Mechanical Code, chapter 1346, and shall be covered with
corrosion resistant screen of not less than one-fourth inch (6.4 mm) mesh.
Intake openings shall be located at least 12 inches (305 mm) above adjoining
grade level.
Exception: Combination air intake and exhaust
hoods may be approved by the building official when specifically allowed by the
equipment manufacturer's installation instructions.
N1104.4.8
Filtration.
Mechanically supplied outdoor air shall have a filter with a designated minimum
efficiency of MERV 4 as defined by ASHRAE Standard 52.2. The filter shall be
located prior to the air entering the thermal conditioning components, blower,
or habitable space and shall be installed to be readily accessible and
facilitate regular service.
N1104.4.9
Noise and vibration.
Mechanical ventilation system components shall be installed to minimize noise
and vibration transmission. The equipment manufacturer's installation
instructions shall be followed, and materials provided by the equipment
manufacturer shall be used for this purpose. In the absence of specific
materials or instructions, vibration dampening materials such as rubber
grommets and flexible straps shall be used when connecting fans and heat
exchangers to the building structure, and isolation duct connectors shall be
used to mitigate noise transmission.
N1104.4.10
Controls. Mechanical
ventilation system controls shall be provided according to the following.
1. Controls shall be installed to ensure that
the forced air circulation system is operating whenever the mechanical
ventilation system is operating if required by the equipment manufacturer's
installation instructions.
2.
Controls shall be installed to ensure that whenever the mechanical ventilation
system is operating, the forced air circulation system provides indirect
circulation of 0.15 cfm per square foot of conditioned floor area or direct
distribution of 0.075 cfm per square foot of conditioned floor area.
3. If the mechanical ventilation system is
not designed to operate whenever the forced air circulation system is
operating, the mechanical ventilation system shall incorporate an accessible
backflow damper to prevent flow from the outside when the mechanical
ventilation system is off.
4.
Controls shall be compatible with the mechanical ventilation system.
5. Controls shall be installed to operate the
mechanical ventilation system as designed.
6. Controls shall be readily accessible to
occupants and shall be labeled to indicate their function.
7. If a switch is used for continuous
ventilation, it can be located centrally or remotely, but shall not be located
in a bath or toilet room. If centrally located, it shall be properly labeled
and lighted when the system is on. If remotely located, there shall be a
lighted status indicator in a central location that will be lighted when the
system is on.
N1104.4.11
Labeling. The
outdoor air intake and exhaust air outlet shall include a permanent, weather
resistant identification label stating "OUTDOOR AIR INTAKE" or "EXHAUST AIR
OUTLET" as appropriate. Controls provided for continuous and intermittent
ventilation shall be provided with a label stating "VENTILATION SYSTEM" or
"VENTILATION FAN" or "INTERMITTENT FAN" or ventilation symbols, as
appropriate.
N1104.4.12
Documentation. Mechanical ventilation systems shall be provided with
documentation that includes proper operation and maintenance instructions and a
warning regarding potential problems if the system is not operated and
maintained. A permanent warning label shall be affixed to a mechanical
ventilation system if it is readily accessible. If the mechanical ventilation
system is not readily accessible, the documentation shall be in a conspicuous
readily accessible location.
N1104.4.13
Climatic design
conditions.A. HVAC equipment must be
sized according to the 2005 ASHRAE Handbook of Fundamentals, ACCA Manual J, or
an equivalent method. Oversizing of heating equipment must not exceed 43
percent and cooling equipment must not exceed 21 percent.
B. Design conditions must be determined from
Table N1104.4.13. Design condition adjustments may be made as determined by the
building official to reflect local climates that differ from the tabulated
temperatures or local weather experience.
| TABLE N1104.4.13 |
| Outdoor Design Conditions |
| City |
Summer Db/Wb
oF |
Winter Db
oF |
| Aitkin |
82/72 |
-24 |
| Albert Lea |
85/72 |
-15 |
| Alexandria |
86/70 |
-21 |
| Bemidji |
84/68 |
-24 |
| Cloquet |
82/68 |
-20 |
| Crookston |
84/70 |
-27 |
| Duluth |
81/67 |
-20 |
| Ely |
82/68 |
-29 |
| Eveleth |
82/68 |
-26 |
| Faribault |
86/73 |
-16 |
| Fergus Falls |
86/71 |
-21 |
| Grand Rapids |
81/67 |
-23 |
| Hibbing |
82/68 |
-19 |
| International Falls |
83/67 |
-28 |
| Litchfield |
85/71 |
-18 |
| Little Falls |
86/71 |
-20 |
| Mankato |
86/72 |
-15 |
| Minneapolis/St. Paul |
88/72 |
-15 |
| Montevideo |
86/72 |
-17 |
| Mora |
84/70 |
-21 |
| Morris |
84/72 |
-21 |
| New Ulm |
87/73 |
-15 |
| Owatonna |
86/73 |
-16 |
| Pequot Lake |
84/68 |
-23 |
| Pipestone |
85/73 |
-15 |
| Redwood Falls |
89/73 |
-17 |
| Rochester |
85/72 |
-17 |
| Roseau |
82/70 |
-29 |
| St. Cloud |
86/71 |
-20 |
| Thief River Falls |
82/68 |
-25 |
| Tofte |
75/61 |
-14 |
| Warroad |
83/67 |
-29 |
| Wheaton |
84/71 |
-20 |
| Willmar |
85/71 |
-20 |
| Winona |
88/74 |
-13 |
| Worthington |
84/71 |
-14 |
| Db = dry bulb temperature, degrees Fahrenheit |
| Wb = wet bulb temperature, degrees Fahrenheit |
