Building HVAC Requirements – Indoor Air Quality and Mechanical Ventilation
Example 4-21 – Ducting Kitchen Exhaust to the Outdoors
Question:
How do I know what kind of duct I need to use? I’ve been using recirculating hoods my
entire career, now I need to vent to the outdoors. How do I do it?
Answer:
A kitchen range hood or downdraft duct is generally a smooth metal duct that is sized to
match the outlet of the ventilation device. It is often a six-inch or seven-inch-round duct, or
the range hood may have a rectangular discharge. If it is rectangular, the fan will typically
have a rectangular-to-round adapter included. Always use a terminal device on the roof or
wall that is sized to be at least as large as the duct. Try to minimize the number of elbows
used.
Example 4-22
Question:
How do I know what the requirements are in my area?
Answer:
Ask your code enforcement agency for that information. Some enforcement agencies will
accept metal flex; some will not.
A. Control and Operation for Intermittent Local Exhaust
The choice of control is left to the designer. It can be a manual switch or automatic
control like an occupancy sensor. Some exhaust fans have multiple speeds, and
some fan controls have a delay-off function that operates the exhaust fan for a set
time after the occupant leaves the bathroom. New control strategies continue to
come to the market. The only requirement is that there is a control. Title 24, Part
11 may specify additional requirements for the control and operation of intermittent
local exhaust.
B. Ventilation Rate for Demand-Controlled Local Exhaust
A minimum exhaust airflow of 100 CFM is required for vented kitchen range hoods,
and 300 CFM or 5 ACH is required for other kitchen exhaust fans. A minimum
exhaust airflow of 50 CFM is required for bathroom fans.
The 100 CFM requirement for the range hood or microwave/hood combination is
the minimum to adequately capture the moisture, particulates, and other products
of cooking and/or combustion. Only in kitchens that are enclosed, the exhaust
requirement can also be met with either a ceiling or wall-mounted exhaust fan or
with a ducted fan or ducted ventilation system that can provide at least five air
changes of the kitchen volume per hour. Recirculating range hoods that do not
exhaust pollutants to the outside cannot be used to meet the requirements of
ASHRAE Standard 62.2 unless paired with an exhaust system that can provide at
least five air changes of the kitchen volume per hour.
,Building HVAC Requirements – Indoor Air Quality and Mechanical Ventilation
The 2019 Title 24 Part 6 standards require verification that range hoods are HVI-
certified to provide at least one speed setting at which they can deliver at least 100
CFM at a noise level of 3 sones or less. Verification must be in accordance with
the procedures in Reference Residential Appendix RA3.7.4.3. Range hoods that
have a minimum airflow setting exceeding 400 CFM are exempt from the noise
requirement.
ASHRAE Standard 62.2 limits exhaust airflow when atmospherically vented
combustion appliances are located inside the pressure boundary. This is
particularly important to observe when large range hoods are installed. Refer to
Section 4.6.8.4 below for more information.
Example 4-23 – Ceiling or Wall Exhaust vs Demand-Controlled Range Hood in an
Enclosed Kitchen
Question:
I am building a house with an enclosed kitchen that is 12 ft. x 14 ft. with a 10 ft. ceiling.
What size ceiling exhaust fan or range hood fan is required?
Answer:
If a range hood exhaust is not used, either 300 CFM or 5 ACH minimum airflow is
required. The kitchen volume is 12 ft. x 14 ft. x 10 ft. = 1,680 ft3. Five air changes are a
flow rate of 1,680 ft³ x 5/ hr. ÷ 60 min/hr = 140 CFM. So, this kitchen must have a ceiling
or wall exhaust fan of 140 CFM. Otherwise, a vented range hood fan that provides at
least 100 CFM is required.
4.6.7.2 Continuous Local Exhaust
The Energy Standards allow the designer to install a local exhaust system that
operates without occupant intervention continuously and automatically during all
occupiable hours. Continuous local exhaust is generally specified when the local
exhaust ventilation system is combined with a continuous dwelling unit ventilation
system. For example, if the dwelling unit ventilation is provided by a continuously
operating exhaust fan located in the bathroom, this fan may also satisfy the local
exhaust requirement for that bathroom, provided the fan provides airflow greater
than or equal to the minimum continuous local ventilation airflow rate. Continuous
local exhaust may also be part of a pickup, or an interior grille, for a remote fan or
HRV/ERV system.
Continuously operating bathroom fans must operate at a minimum of 20 CFM.
Continuously operating kitchen fans are permitted only for enclosed kitchens. Refer
to Tables 5.1 and 5.2 in ASHRAE 62.2 for other local demand controlled and
continuous exhaust requirements.
Example 4-24 – Continuous Kitchen Exhaust
Question:
,Building HVAC Requirements – Indoor Air Quality and Mechanical Ventilation
A new house has an open-design, 12 ft. x18 ft. ranch kitchen with 12 ft. cathedral ceilings.
What airflow rate will be required for a continuous exhaust fan?
Answer:
A continuous exhaust fan cannot be used in nonenclosed kitchens. A vented range hood
must be provided.
4.6.2 Other Requirements (Section 6 of ASHRAE 62.2)
4.6.8.1 Adjacent Spaces and Transfer Air
From ASHRAE 62.2,
6.1 Adjacent Spaces and Transfer Air. Measures shall be taken to minimize air
movement across envelope components to dwelling units from adjacent spaces
such as garages, unconditioned crawlspaces, unconditioned attics, and other
dwelling units. Pressure boundary wall, ceiling, and floor penetrations shall be
sealed, as shall any vertical chases adjacent to dwelling units. Doors between
dwelling units and common hallways shall begasketed or made substantially
airtight.
Supply and balanced ventilation systems shall be designed and constructedto
provide ventilation air directly from the outdoors.
6.1.1 Compliance for Attached Dwelling Units. One method of demonstrating
compliance with Section 6.1 shall be to verify a leakage rate below a maximum of
0.3 CFM per ft2 (150 L/s per 100 m2) of the dwelling unit envelope area (i.e., the
sum of the area of walls between dwelling units, exterior walls, ceiling, and floor)
at a test pressure of 50 Pa by a blower doortest conducted in accordance with
either ANSI/ASTM-E779 or ANSI/ASTM- E1827. The test shall be conducted with
the dwelling unit as if it were exposed to outdoor air on all sides, top, and bottom
by opening doors and windows of adjacent dwelling units.
ASHRAE Standard 62.2 requires that the air used for ventilation come from the
outdoors. Air may not be drawn in as transfer air from other spaces that are outside
the occupiable space of the dwelling unit, or from between dwelling units and
corridors. This is to prevent airborne pollutants originating in those other spaces from
contaminating the dwelling unit. For example, drawing ventilation air from the garage
could introduce VOCs or pesticides into the indoor air. Drawing ventilation air from
an unconditioned crawlspace could cause elevated allergen concentrations in the
dwelling such as mold spores, insects, or rodent allergens. Likewise, drawing air
from an adjacent dwelling could introduce unwanted contaminants such as cooking
odors or cigarette smoke.
Standards Section 150.0(o)1E requires HERS verification compliance with a
maximum of 0.3 CFM/ft2 dwelling unit enclosure leakage when either supply
ventilation is used or exhaust ventilation is used. The protocol for the blower door
test is given in Reference Residential Appendix RA3.8. See also Section 4.6.3.2 in
, Building HVAC Requirements – Indoor Air Quality and Mechanical Ventilation
this chapter for more information about multifamily dwelling unit
compartmentalization.
In addition to designing the ventilation system to draw air from the outdoors, the
standard also requires that measures be taken to prevent air movement between
adjacent dwelling units and between the dwelling unit and other nearby spaces, such
as garages. The measures can include air sealing of envelope components,
pressure management, and use of airtight recessed light fixtures. The measures
must apply to adjacent units above and below, as well as side by side.
Air sealing must include pathways in vertical components such as demising walls
and walls common to the unit and an attached garage, and in horizontal components
such as floors and ceilings. Pipe and electrical penetrations are examples of
pathways that require sealing.
4.6.8.2 Instructions and Labeling
From ASHRAE 62.2, Section 6.2, Instructions and Labeling.
Information on the ventilation design and/or ventilation systems installed,
instructions on their proper operation to meet the requirements of this
standard, and instructions detailing any required maintenance (similar to
that provided for HVAC systems) shall be provided to the owner and the
occupant of the dwelling unit. Controls shall be labeled as to their function
(unless that function is obvious, such as toilet exhaust fan switches).
From Standards Section 150.0(o)1I:
Compliance with ASHRAE 62.2 Section 4.4 (Control and Operation) shall
require manual switches associated with dwelling unit ventilation systems to
have a label clearly displaying the following text, or equivalent text: "This
switch controls the indoor air quality ventilation for the home. Leave it on
unless the outdoor air quality is very poor.
Field studies have shown that switches for exhaust fans do not have the required
labels, and that many homeowners do not understand the importance of continuous
operation of the ventilation fans for maintaining indoor air quality. Standards Section
10-103(b)4 require the builder to leave in the building, for the building owner at
occupancy, a description of the quantities of outdoor air that the ventilation system(s)
are designed to provide to the conditioned space of the building and instructions for
proper operation and maintenance of the ventilation system.
Because the concept of a designed dwelling unit ventilation system may be new to
many occupants, the standards section requires that ventilation system controls be
labeled as to function. One acceptable option is to affix a label to the electrical panel
that provides some basic system operation information.
Example 4-21 – Ducting Kitchen Exhaust to the Outdoors
Question:
How do I know what kind of duct I need to use? I’ve been using recirculating hoods my
entire career, now I need to vent to the outdoors. How do I do it?
Answer:
A kitchen range hood or downdraft duct is generally a smooth metal duct that is sized to
match the outlet of the ventilation device. It is often a six-inch or seven-inch-round duct, or
the range hood may have a rectangular discharge. If it is rectangular, the fan will typically
have a rectangular-to-round adapter included. Always use a terminal device on the roof or
wall that is sized to be at least as large as the duct. Try to minimize the number of elbows
used.
Example 4-22
Question:
How do I know what the requirements are in my area?
Answer:
Ask your code enforcement agency for that information. Some enforcement agencies will
accept metal flex; some will not.
A. Control and Operation for Intermittent Local Exhaust
The choice of control is left to the designer. It can be a manual switch or automatic
control like an occupancy sensor. Some exhaust fans have multiple speeds, and
some fan controls have a delay-off function that operates the exhaust fan for a set
time after the occupant leaves the bathroom. New control strategies continue to
come to the market. The only requirement is that there is a control. Title 24, Part
11 may specify additional requirements for the control and operation of intermittent
local exhaust.
B. Ventilation Rate for Demand-Controlled Local Exhaust
A minimum exhaust airflow of 100 CFM is required for vented kitchen range hoods,
and 300 CFM or 5 ACH is required for other kitchen exhaust fans. A minimum
exhaust airflow of 50 CFM is required for bathroom fans.
The 100 CFM requirement for the range hood or microwave/hood combination is
the minimum to adequately capture the moisture, particulates, and other products
of cooking and/or combustion. Only in kitchens that are enclosed, the exhaust
requirement can also be met with either a ceiling or wall-mounted exhaust fan or
with a ducted fan or ducted ventilation system that can provide at least five air
changes of the kitchen volume per hour. Recirculating range hoods that do not
exhaust pollutants to the outside cannot be used to meet the requirements of
ASHRAE Standard 62.2 unless paired with an exhaust system that can provide at
least five air changes of the kitchen volume per hour.
,Building HVAC Requirements – Indoor Air Quality and Mechanical Ventilation
The 2019 Title 24 Part 6 standards require verification that range hoods are HVI-
certified to provide at least one speed setting at which they can deliver at least 100
CFM at a noise level of 3 sones or less. Verification must be in accordance with
the procedures in Reference Residential Appendix RA3.7.4.3. Range hoods that
have a minimum airflow setting exceeding 400 CFM are exempt from the noise
requirement.
ASHRAE Standard 62.2 limits exhaust airflow when atmospherically vented
combustion appliances are located inside the pressure boundary. This is
particularly important to observe when large range hoods are installed. Refer to
Section 4.6.8.4 below for more information.
Example 4-23 – Ceiling or Wall Exhaust vs Demand-Controlled Range Hood in an
Enclosed Kitchen
Question:
I am building a house with an enclosed kitchen that is 12 ft. x 14 ft. with a 10 ft. ceiling.
What size ceiling exhaust fan or range hood fan is required?
Answer:
If a range hood exhaust is not used, either 300 CFM or 5 ACH minimum airflow is
required. The kitchen volume is 12 ft. x 14 ft. x 10 ft. = 1,680 ft3. Five air changes are a
flow rate of 1,680 ft³ x 5/ hr. ÷ 60 min/hr = 140 CFM. So, this kitchen must have a ceiling
or wall exhaust fan of 140 CFM. Otherwise, a vented range hood fan that provides at
least 100 CFM is required.
4.6.7.2 Continuous Local Exhaust
The Energy Standards allow the designer to install a local exhaust system that
operates without occupant intervention continuously and automatically during all
occupiable hours. Continuous local exhaust is generally specified when the local
exhaust ventilation system is combined with a continuous dwelling unit ventilation
system. For example, if the dwelling unit ventilation is provided by a continuously
operating exhaust fan located in the bathroom, this fan may also satisfy the local
exhaust requirement for that bathroom, provided the fan provides airflow greater
than or equal to the minimum continuous local ventilation airflow rate. Continuous
local exhaust may also be part of a pickup, or an interior grille, for a remote fan or
HRV/ERV system.
Continuously operating bathroom fans must operate at a minimum of 20 CFM.
Continuously operating kitchen fans are permitted only for enclosed kitchens. Refer
to Tables 5.1 and 5.2 in ASHRAE 62.2 for other local demand controlled and
continuous exhaust requirements.
Example 4-24 – Continuous Kitchen Exhaust
Question:
,Building HVAC Requirements – Indoor Air Quality and Mechanical Ventilation
A new house has an open-design, 12 ft. x18 ft. ranch kitchen with 12 ft. cathedral ceilings.
What airflow rate will be required for a continuous exhaust fan?
Answer:
A continuous exhaust fan cannot be used in nonenclosed kitchens. A vented range hood
must be provided.
4.6.2 Other Requirements (Section 6 of ASHRAE 62.2)
4.6.8.1 Adjacent Spaces and Transfer Air
From ASHRAE 62.2,
6.1 Adjacent Spaces and Transfer Air. Measures shall be taken to minimize air
movement across envelope components to dwelling units from adjacent spaces
such as garages, unconditioned crawlspaces, unconditioned attics, and other
dwelling units. Pressure boundary wall, ceiling, and floor penetrations shall be
sealed, as shall any vertical chases adjacent to dwelling units. Doors between
dwelling units and common hallways shall begasketed or made substantially
airtight.
Supply and balanced ventilation systems shall be designed and constructedto
provide ventilation air directly from the outdoors.
6.1.1 Compliance for Attached Dwelling Units. One method of demonstrating
compliance with Section 6.1 shall be to verify a leakage rate below a maximum of
0.3 CFM per ft2 (150 L/s per 100 m2) of the dwelling unit envelope area (i.e., the
sum of the area of walls between dwelling units, exterior walls, ceiling, and floor)
at a test pressure of 50 Pa by a blower doortest conducted in accordance with
either ANSI/ASTM-E779 or ANSI/ASTM- E1827. The test shall be conducted with
the dwelling unit as if it were exposed to outdoor air on all sides, top, and bottom
by opening doors and windows of adjacent dwelling units.
ASHRAE Standard 62.2 requires that the air used for ventilation come from the
outdoors. Air may not be drawn in as transfer air from other spaces that are outside
the occupiable space of the dwelling unit, or from between dwelling units and
corridors. This is to prevent airborne pollutants originating in those other spaces from
contaminating the dwelling unit. For example, drawing ventilation air from the garage
could introduce VOCs or pesticides into the indoor air. Drawing ventilation air from
an unconditioned crawlspace could cause elevated allergen concentrations in the
dwelling such as mold spores, insects, or rodent allergens. Likewise, drawing air
from an adjacent dwelling could introduce unwanted contaminants such as cooking
odors or cigarette smoke.
Standards Section 150.0(o)1E requires HERS verification compliance with a
maximum of 0.3 CFM/ft2 dwelling unit enclosure leakage when either supply
ventilation is used or exhaust ventilation is used. The protocol for the blower door
test is given in Reference Residential Appendix RA3.8. See also Section 4.6.3.2 in
, Building HVAC Requirements – Indoor Air Quality and Mechanical Ventilation
this chapter for more information about multifamily dwelling unit
compartmentalization.
In addition to designing the ventilation system to draw air from the outdoors, the
standard also requires that measures be taken to prevent air movement between
adjacent dwelling units and between the dwelling unit and other nearby spaces, such
as garages. The measures can include air sealing of envelope components,
pressure management, and use of airtight recessed light fixtures. The measures
must apply to adjacent units above and below, as well as side by side.
Air sealing must include pathways in vertical components such as demising walls
and walls common to the unit and an attached garage, and in horizontal components
such as floors and ceilings. Pipe and electrical penetrations are examples of
pathways that require sealing.
4.6.8.2 Instructions and Labeling
From ASHRAE 62.2, Section 6.2, Instructions and Labeling.
Information on the ventilation design and/or ventilation systems installed,
instructions on their proper operation to meet the requirements of this
standard, and instructions detailing any required maintenance (similar to
that provided for HVAC systems) shall be provided to the owner and the
occupant of the dwelling unit. Controls shall be labeled as to their function
(unless that function is obvious, such as toilet exhaust fan switches).
From Standards Section 150.0(o)1I:
Compliance with ASHRAE 62.2 Section 4.4 (Control and Operation) shall
require manual switches associated with dwelling unit ventilation systems to
have a label clearly displaying the following text, or equivalent text: "This
switch controls the indoor air quality ventilation for the home. Leave it on
unless the outdoor air quality is very poor.
Field studies have shown that switches for exhaust fans do not have the required
labels, and that many homeowners do not understand the importance of continuous
operation of the ventilation fans for maintaining indoor air quality. Standards Section
10-103(b)4 require the builder to leave in the building, for the building owner at
occupancy, a description of the quantities of outdoor air that the ventilation system(s)
are designed to provide to the conditioned space of the building and instructions for
proper operation and maintenance of the ventilation system.
Because the concept of a designed dwelling unit ventilation system may be new to
many occupants, the standards section requires that ventilation system controls be
labeled as to function. One acceptable option is to affix a label to the electrical panel
that provides some basic system operation information.
