For more information, contact:

Energy Efficiency and

Renewable Energy

Clearinghouse (EREC)

1-800-DOE-3732

www.eren.doe.gov

Or visit the Building

Technologies Program

Web site at

www.buildings.gov

Or refer to Understanding

Ventilation: How to Design,

Select, and Install Residential

Ventilation Systems

The Healthy House Institute

812-332-5073

www.hhinst.com

Written and prepared for

the U.S. Department of

Energy by:

NAHB Research Center

800-898-2842

www.nahbrc.org

Southface Energy Institute

404-872-3549

www.southface.org

U.S. Department of Energy’s

Oak Ridge National

Laboratory

Buildings Technology Center

865-574-5206

www.ornl.gov/btc

U.S. Department of Energy’s

National Renewable Energy

Laboratory

303-275-3000

www.nrel.gov/buildings

NOTICE: Neither the United States

government nor any agency

thereof, nor any of their employees,

makes any warranty, express or

implied, or assumes any legal

liability or responsibility for the

accuracy, completeness, or

usefulness of any information,

apparatus, product, or process

disclosed. The views and opinions

of authors expressed herein do not

necessarily state or reflect those of

the United States government or

any agency thereof.

SPOT VENTILATION

Printed with a renewable-source ink on paper containing at

least 50% wastepaper, including 20% postconsumer waste.

December 2002 DOE/GO-102002-0786

DESIGN SPECIFICATIONS

CAPACITY REQUIREMENTS

Bath fans should be sized to provide the larger of

50 cfm or 8 ACH in the bathroom. The required

cfm capacity to provide 8 ACH can be calculated

by multiplying the volume of the bathroom in

cubic feet by 8 and dividing by 60.

Kitchen range hood fans should have a capacity

of at least 100 cfm or 40 cfm per linear foot of

hood, whichever is larger. For peninsula or island

ranges, the fan capacity should be based on the

combined length of the exposed three or four sides

of the hood. If the hood is more than 27" above the

range surface, the capacity should be increased.

The capacity of both bath and range hood fans is

typically provided at 0.1" and 0.25" of static

pressure to account for different duct types, duct

length, duct configuration (number of turns and

elbows), and exhaust termination. See the fan

manufacturer’s recommendations to determine

the fan’s capacity based on these duct

characteristics. Generally, the capacity at 0.25"

should be used. The capacity at 0.1" is usually

appropriate only if the duct is smooth, straight

(one elbow or less), and less than 15' in length. If

the duct is longer than 15', has a diameter of less

than 4", requires the use of multiple elbows, and/

or uses corrugated duct material, the capacity

achieved in the actual installation may be less

than even the 0.25" capacity rating.

EFFICACY

Fan efficacy refers to the energy needed to move

a specified amount of air. To calculate fan

efficacy, divide fan capacity (in cfm) by power

consumption (in watts)—the larger the ratio the

better. Both capacity and power consumption

values are available from the manufacturer’s

literature or the product container. Consider the

use of Energy Star® rated fans to reduce operation

costs. To receive the Energy Star label, small bath

fans (up to 75 cfm) must achieve 1.4 cfm/W or

higher and larger bath fans and range hoods up

to 500 cfm must achieve at least 2.8 cfm/W.

NOISE

Noise is a major reason people avoid using

ventilation fans. Small bathroom fans (less than

76 cfm) must have sound levels of no more than

2.0 sones to be labeled as Energy Star compliant;

large bathroom fans must have sound levels of no

more than 1.5 sones. Bath fans with noise levels

of 1 sone or less are also available and should be

considered to eliminate noise problems.

To receive the Energy Star label, range fans must

have sound levels of no more than 4.0 sones. The

quietest kitchen range hoods are rated at less than

2 sones. If multi-speed fans are used, be sure that

the sound level at the high speed is 4 sones or less.

Remotely mounted fans are not typically soundrated because various factors affect the perceived

interior sound levels.

INSTALLATION

MOUNTING

Seal gaskets and fan housings mounted on

ceilings or walls. In insulated assemblies, do not use

fans that are not rated for insulation contact.

DUCTS

The most efficient fan ducts are smooth, short,

straight, and properly sized. Smooth sheet metal

ducts offer low airflow resistance. Because

corrugated ducts have greater flow resistance, it is

important to keep them as short as possible—

stretch the corrugated material to its full length and

cut off excess. Minimize the number of elbows. Seal

joints with duct mastic. To inhibit condensation

problems in unheated spaces, insulate the ducts

and slope the ducts away from the fan. Ducts

should match or exceed the fan duct fitting size.

DUCT TERMINATION

Ducts expelling water vapor or other pollutants

must exhaust directly to the exterior—never into

attics or crawl spaces prone to moisture problems.

Use wall caps or roof jacks with flap dampers,

screens, or both to deter access. Unless they are

already integrated into the system (e.g., wall cap

with flapper), equip ventilation ducts with backdraft

dampers at or near the insulated building boundary

to reduce infiltration.
SPOT VENTILATION DESIGN

Building codes may provide specific requirements concerning

spot ventilation. Generally, the guidelines in this fact sheet meet or

exceed code requirements; however, it is important to consult

local codes and code officials before sizing and installing spot

ventilation systems.

Spot ventilation is recommended for bathrooms and kitchen

ranges. Bathroom windows are seldom opened in cold or hot

weather. Recirculating range hoods do not remove cookinggenerated moisture from the living space and are not generally

effective at controlling odors. Therefore, these are considered

poor substitutes for directly exhausting polluted air from these

locations to the outside.

Spot ventilation fans are intended to reduce concentrations of

moisture or pollutants in the living space. Inevitably, they exhaust

clean room air along with the moist or polluted air. To maximize

effectiveness,

• Exhaust fans should be located as close as possible to the

sources of moisture or pollutants. In the kitchen, range hoods

that exhaust to the outside are preferable to kitchen vent fans

because most kitchen moisture and pollution come from the

range. Hood-mounted range fans are also preferable to

surface-mounted downdraft cooktop vents. Although surfacemounted vents are located close to the source of the

pollution, they are less effective than hood-mounted fans

because the downdraft design must overcome the buoyancy

of warm, polluted air coming from the cooking surface.

• Space heating and cooling registers should be located as far

as practical from exhaust vents to minimize the amount of

conditioned air that is directly exhausted with the polluted air.

• Automatic or manual controls should be installed to allow the

fan to operate only when needed.

Spot ventilation exhaust fans produce noise that can disrupt

household activities and discourage people from using them.

Several manufacturers offer low-noise fans to minimize this

problem. Spot ventilation designs that require mounting fans on

walls and ceilings can be modified to use fans that can be

mounted in-line in the duct between the living space and the

exterior, or on the roof or outside wall and connected to the room

by a duct. The space between the in-line or exterior-mounted fan

and the interior reduces the noise level in the house.

SPOT VENTILATION ISSUES

Spot ventilation may contribute to unacceptable radon levels

inside the house if fan operation draws in radon-contaminated air

via leaks in the floor, although this is less an issue for intermittent

fan operation. Local codes or building officials should be able to

indicate whether radon levels are an issue. Sealing leaks in the

floor is an essential first course of action. If this is not sufficient

to reduce radon pollution to acceptable levels, a radon mitigation

system and/or a supply-only or balanced whole-house ventilation

system may be necessary. See http://www.epa.gov/iaq/radon/

construc.html for additional information.

Operation of spot ventilation exhaust fans can induce

backdrafting—spillage of flue gases from combustion appliances

(e.g., furnace, water heater, fireplace) into the living space—

primarily when atmospheric or natural-draft flues are used rather

than powered combustion systems. Elevated concentrations of

pollutants in flue gases can pose serious health hazards. When

using natural gas appliances, these problems can be avoided by

• using sealed-combustion models or models with powervented exhausts,

• installing natural-draft combustion units in airtight

mechanical enclosures that are vented to the outside, or

• placing natural-draft combustion units outside the

conditioned space.

FAN TYPES

Ceiling-mounted—Ducted, ceiling-mounted fans common in

bathrooms have capacities ranging from 50 to over 200 cfm.

Through-the-wall—Kitchens, baths, and some laundry areas

have historically used through-the-wall fans to directly exhaust

indoor air to the outdoors. These are simple but often not airtight

when closed. Capacities range from 175 to over 500 cfm.

Kitchen range hood—Kitchen range fans capture pollutants and

moisture generated by cooking and exhaust to the outdoors.

Standard, updraft range hood units come efficiently positioned to

make them most effective, are competitively priced, and use little

total energy. Ductless recirculating units do not control moisture

or other pollutants and should be avoided. Surface-mounted or

snorkel (pop-up) downdraft units, popular for their convenience,

tend to be costlier and less effective than overhead units.
SPOT VENTILATION DESIGN

Building codes may provide specific requirements concerning

spot ventilation. Generally, the guidelines in this fact sheet meet or

exceed code requirements; however, it is important to consult

local codes and code officials before sizing and installing spot

ventilation systems.

Spot ventilation is recommended for bathrooms and kitchen

ranges. Bathroom windows are seldom opened in cold or hot

weather. Recirculating range hoods do not remove cookinggenerated moisture from the living space and are not generally

effective at controlling odors. Therefore, these are considered

poor substitutes for directly exhausting polluted air from these

locations to the outside.

Spot ventilation fans are intended to reduce concentrations of

moisture or pollutants in the living space. Inevitably, they exhaust

clean room air along with the moist or polluted air. To maximize

effectiveness,

• Exhaust fans should be located as close as possible to the

sources of moisture or pollutants. In the kitchen, range hoods

that exhaust to the outside are preferable to kitchen vent fans

because most kitchen moisture and pollution come from the

range. Hood-mounted range fans are also preferable to

surface-mounted downdraft cooktop vents. Although surfacemounted vents are located close to the source of the

pollution, they are less effective than hood-mounted fans

because the downdraft design must overcome the buoyancy

of warm, polluted air coming from the cooking surface.

• Space heating and cooling registers should be located as far

as practical from exhaust vents to minimize the amount of

conditioned air that is directly exhausted with the polluted air.

• Automatic or manual controls should be installed to allow the

fan to operate only when needed.

Spot ventilation exhaust fans produce noise that can disrupt

household activities and discourage people from using them.

Several manufacturers offer low-noise fans to minimize this

problem. Spot ventilation designs that require mounting fans on

walls and ceilings can be modified to use fans that can be

mounted in-line in the duct between the living space and the

exterior, or on the roof or outside wall and connected to the room

by a duct. The space between the in-line or exterior-mounted fan

and the interior reduces the noise level in the house.

SPOT VENTILATION ISSUES

Spot ventilation may contribute to unacceptable radon levels

inside the house if fan operation draws in radon-contaminated air

via leaks in the floor, although this is less an issue for intermittent

fan operation. Local codes or building officials should be able to

indicate whether radon levels are an issue. Sealing leaks in the

floor is an essential first course of action. If this is not sufficient

to reduce radon pollution to acceptable levels, a radon mitigation

system and/or a supply-only or balanced whole-house ventilation

system may be necessary. See http://www.epa.gov/iaq/radon/

construc.html for additional information.

Operation of spot ventilation exhaust fans can induce

backdrafting—spillage of flue gases from combustion appliances

(e.g., furnace, water heater, fireplace) into the living space—

primarily when atmospheric or natural-draft flues are used rather

than powered combustion systems. Elevated concentrations of

pollutants in flue gases can pose serious health hazards. When

using natural gas appliances, these problems can be avoided by

• using sealed-combustion models or models with powervented exhausts,

• installing natural-draft combustion units in airtight

mechanical enclosures that are vented to the outside, or

• placing natural-draft combustion units outside the

conditioned space.

FAN TYPES

Ceiling-mounted—Ducted, ceiling-mounted fans common in

bathrooms have capacities ranging from 50 to over 200 cfm.

Through-the-wall—Kitchens, baths, and some laundry areas

have historically used through-the-wall fans to directly exhaust

indoor air to the outdoors. These are simple but often not airtight

when closed. Capacities range from 175 to over 500 cfm.

Kitchen range hood—Kitchen range fans capture pollutants and

moisture generated by cooking and exhaust to the outdoors.

Standard, updraft range hood units come efficiently positioned to

make them most effective, are competitively priced, and use little

total energy. Ductless recirculating units do not control moisture

or other pollutants and should be avoided. Surface-mounted or

snorkel (pop-up) downdraft units, popular for their convenience,

tend to be costlier and less effective than overhead units.
For more information, contact:

Energy Efficiency and

Renewable Energy

Clearinghouse (EREC)

1-800-DOE-3732

www.eren.doe.gov

Or visit the Building

Technologies Program

Web site at

www.buildings.gov

Or refer to Understanding

Ventilation: How to Design,

Select, and Install Residential

Ventilation Systems

The Healthy House Institute

812-332-5073

www.hhinst.com

Written and prepared for

the U.S. Department of

Energy by:

NAHB Research Center

800-898-2842

www.nahbrc.org

Southface Energy Institute

404-872-3549

www.southface.org

U.S. Department of Energy’s

Oak Ridge National

Laboratory

Buildings Technology Center

865-574-5206

www.ornl.gov/btc

U.S. Department of Energy’s

National Renewable Energy

Laboratory

303-275-3000

www.nrel.gov/buildings

NOTICE: Neither the United States

government nor any agency

thereof, nor any of their employees,

makes any warranty, express or

implied, or assumes any legal

liability or responsibility for the

accuracy, completeness, or

usefulness of any information,

apparatus, product, or process

disclosed. The views and opinions

of authors expressed herein do not

necessarily state or reflect those of

the United States government or

any agency thereof.

SPOT VENTILATION

Printed with a renewable-source ink on paper containing at

least 50% wastepaper, including 20% postconsumer waste.

December 2002 DOE/GO-102002-0786

DESIGN SPECIFICATIONS

CAPACITY REQUIREMENTS

Bath fans should be sized to provide the larger of

50 cfm or 8 ACH in the bathroom. The required

cfm capacity to provide 8 ACH can be calculated

by multiplying the volume of the bathroom in

cubic feet by 8 and dividing by 60.

Kitchen range hood fans should have a capacity

of at least 100 cfm or 40 cfm per linear foot of

hood, whichever is larger. For peninsula or island

ranges, the fan capacity should be based on the

combined length of the exposed three or four sides

of the hood. If the hood is more than 27" above the

range surface, the capacity should be increased.

The capacity of both bath and range hood fans is

typically provided at 0.1" and 0.25" of static

pressure to account for different duct types, duct

length, duct configuration (number of turns and

elbows), and exhaust termination. See the fan

manufacturer’s recommendations to determine

the fan’s capacity based on these duct

characteristics. Generally, the capacity at 0.25"

should be used. The capacity at 0.1" is usually

appropriate only if the duct is smooth, straight

(one elbow or less), and less than 15' in length. If

the duct is longer than 15', has a diameter of less

than 4", requires the use of multiple elbows, and/

or uses corrugated duct material, the capacity

achieved in the actual installation may be less

than even the 0.25" capacity rating.

EFFICACY

Fan efficacy refers to the energy needed to move

a specified amount of air. To calculate fan

efficacy, divide fan capacity (in cfm) by power

consumption (in watts)—the larger the ratio the

better. Both capacity and power consumption

values are available from the manufacturer’s

literature or the product container. Consider the

use of Energy Star® rated fans to reduce operation

costs. To receive the Energy Star label, small bath

fans (up to 75 cfm) must achieve 1.4 cfm/W or

higher and larger bath fans and range hoods up

to 500 cfm must achieve at least 2.8 cfm/W.

NOISE

Noise is a major reason people avoid using

ventilation fans. Small bathroom fans (less than

76 cfm) must have sound levels of no more than

2.0 sones to be labeled as Energy Star compliant;

large bathroom fans must have sound levels of no

more than 1.5 sones. Bath fans with noise levels

of 1 sone or less are also available and should be

considered to eliminate noise problems.

To receive the Energy Star label, range fans must

have sound levels of no more than 4.0 sones. The

quietest kitchen range hoods are rated at less than

2 sones. If multi-speed fans are used, be sure that

the sound level at the high speed is 4 sones or less.

Remotely mounted fans are not typically soundrated because various factors affect the perceived

interior sound levels.

INSTALLATION

MOUNTING

Seal gaskets and fan housings mounted on

ceilings or walls. In insulated assemblies, do not use

fans that are not rated for insulation contact.

DUCTS

The most efficient fan ducts are smooth, short,

straight, and properly sized. Smooth sheet metal

ducts offer low airflow resistance. Because

corrugated ducts have greater flow resistance, it is

important to keep them as short as possible—

stretch the corrugated material to its full length and

cut off excess. Minimize the number of elbows. Seal

joints with duct mastic. To inhibit condensation

problems in unheated spaces, insulate the ducts

and slope the ducts away from the fan. Ducts

should match or exceed the fan duct fitting size.

DUCT TERMINATION

Ducts expelling water vapor or other pollutants

must exhaust directly to the exterior—never into

attics or crawl spaces prone to moisture problems.

Use wall caps or roof jacks with flap dampers,

screens, or both to deter access. Unless they are

already integrated into the system (e.g., wall cap

with flapper), equip ventilation ducts with backdraft

dampers at or near the insulated building boundary

to reduce infiltration.