HomeMy WebLinkAbout2012IRCVentilationRequirements(2), 3.1.21INTERNATIONAL RESIDENTIAL CODE
MECHANICAL VENTILATION AS REQUIRED
BY IOWA 2012 IECC SECTION 403.5
DEFINITIONS
LOCAL EXHAUST. An exhaust system that uses one or
more fans to exhaust air from a specific room or rooms
within a dwelling.
WHOLE HOUSE MECHANICAL VENTILATION
SYSTEM. An exhaust system, supply system, or
combination thereof that is designed to mechanically
exchange indoor air with outdoor air when operating
continuously or through a programmed intermittent schedule
to satisfy the whole house ventilation rates.
SECTION M1507
MECHANICAL VENTILATION
M1507.1 General. Where local exhaust or whole-house
mechanical ventilation is provided, the equipment shall be
designed in accordance with this section.
M1507.2 Recirculation of air. Exhaust air from bathrooms
and toilet rooms shall not be recirculated within a residence
or to another dwelling unit and shall be exhausted directly to
the outdoors. Exhaust air from bathrooms and toilet rooms
shall not discharge into an attic, crawl space or other areas
inside the building.
M1507.3 Whole-house mechanical ventilation system.
Whole-house mechanical ventilation systems shall be
designed in accordance with Sections M1507.3.1 through
M1507.3.3.
M1507.3.1 System design. The whole-house ventilation
system shall consist of one or more supply or exhaust fans,
or a combination of such, and associated ducts and controls.
Local exhaust or supply fans are permitted to serve as such a
system. Outdoor air ducts connected to the return side of an
air handler shall be considered to provide supply ventilation.
M1507.3.2 System controls. The whole-house mechanical
ventilation system shall be provided with controls that
enable manual override.
M1507.3.3 Mechanical ventilation rate. The whole house
mechanical ventilation system shall provide outdoor air at a
continuous rate of not less than that determined in
accordance with Table M1507.3.3(1).
Exception: The whole-house mechanical ventilation system
is permitted to operate intermittently where the system has
controls that enable operation for not less than 25-percent of
each 4-hour segment and the ventilation rate prescribed in
Table M1507.3.3(1) is multiplied by the factor determined in
accordance with Table M1507.3.3(2).
M1507.4 Local exhaust rates. Local exhaust systems shall
be designed to have the capacity to exhaust the minimum air
flow rate determined in accordance with Table M1507.4.
TABLE M1507.4
MINIMUM REQUIRED LOCAL EXHAUST RATES FOR
ONE- AND TWO-FAMILY DWELLINGS
AREA TO BE EXHAUSTED EXHAUST RATES
Kitchens 100 cfm intermittent or 25 cfm
continuous
Bathrooms—Toilet Rooms Mechanical exhaust capacity of 50 cfm
intermittent or 20 cfm continuous
For SI: 1 cubic foot per minute = 0.4719 L/s.
TABLE M1507.3.3(1)
CONTINUOUS WHOLE-HOUSE MECHANICAL VENTILATION SYSTEM AIR FLOW RATE REQUIREMENTS
DWELLING UNIT
FLOOR AREA
(square feet)
NUMBER OF BEDROOMS
0 - 1 2 - 3 4 - 5 6 - 7 >7
Airflow in CFM
<1500 30 45 60 75 90
1501-3000 45 60 75 90 105
3001-4500 60 75 90 105 120
4501-6000 75 90 105 120 135
6001-7500 90 105 120 135 150
>7500 105 120 135 150 165
TABLE M1507.3.3(2)
INTERMITTENT WHOLE-HOUSE MECHANICAL VENTILATION RATE FACTORSa, b
RUN-TIME PERCENTAGE IN
EACH 4 HOUR SEGMENT
25% 33% 50% 66% 75% 100%
Factora 4 3 2 1.5 1.3 1.0
a. For ventilation system run time values between those given, the factors are permitted to be determined by interpolation.
b. Extrapolation beyond the table is prohibited.