Skip to main content

Radon Fan

    Scope
    Scope Images
    Image
    Radon fan– slab-on-grade construction
    Scope

    Install a radon fan or a passive radon vent system to prevent the accumulation of radon and soil gases in the home.

    Install an active radon vent system with fan if

    • the home is built in EPA Radon Zone 1
    • or, the home is tested for radon after construction and shows an indoor radon concentration level of  ≥ 4 picocuries/liter, regardless of what radon zone the home is located in (EPA Indoor airPLUS).

    Install an active radon vent system consisting of an in-line fan installed in a vertical vent pipe extending up from a sub-slab collection pipe or mat through the conditioned space of the home and through the roof that uses the fan to pull soil gases up and out of the house. 

    • Determine vent pipe size and location.
    • Lay a perforated pipe or a collection mat around the interior of the foundation perimeter and insert a vertical “T” pipe connect to the pipe or mat.
    • Install the concrete slab or polyethylene vapor barrier or both over the ground. Ensure that the slab and/or vapor barrier do not cover the vertical opening of the T connector but are sealed around it.
    • Install the vertical pipe.
    • Run the pipe up through the interior of the house and through the roof.
    • Install an in-line fan.

    Install a passive radon venting system if the home is located in Radon Zone 2 or 3. See the guide Vertical Radon Ventilation Pipe.

    • Install a passive radon ventilation system consisting of a vertical vent pipe extending up from a sub-slab collection pipe or mat through the conditioned space of the home and through the roof that uses the natural stack effect to pull soil gases up and out of the house. 
    • Install an electrical outlet in the attic near the vent stack in case a fan needs to be added later.
    • Test the home after construction is completed and add an in-line fan if the indoor radon concentration is ≥ 4 picocuries/liter.

    See the Compliance Tab for related codes and standards and criteria to meet the requirements of national programs such as DOE’s Zero Energy Ready Home programENERGY STAR Single-Family New Homes, and Indoor airPLUS.

     

    Description
    Description

    Radon is a naturally occurring radioactive gas that is estimated to cause approximately 21,000 lung cancer deaths per year in the United States. The amount of radon in the air is measured in “picocuries per liter of air,” or pCi/L. The average outdoor radon level is 0.4 pCi/L. The average indoor radon level is estimated at 1.3 pCi/L. Roughly 1 out of 15 homes in the United States has elevated radon levels (4 pCi/L or greater).

    Radon and other soil gases (water vapor, herbicides, termiticides, methane, etc.) can create an unhealthy indoor environment if they accumulate inside the home. Radon can enter the home through cracks in concrete floors and foundation walls, joints between two or more construction materials, gaps in the materials comprising suspended floors, gaps around foundation penetrations, and cavities inside foundation walls.

    The U.S. Environmental Protection Agency publishes a map indicating likely radon levels across the United States (see Climate tab) and has established a maximum exposure limit of 4 picocuries per liter of indoor air. Regardless of individual county radon zone designation, high indoor radon levels have been found in every state, and factors impacting radon infiltration can be complex, including interactions between soil composition, weather, home design and construction, and ventilation from the HVAC system.

    Because local radon levels may vary from those shown on the county-level EPA radon map, because the amount of radon that will accumulate in a home can’t be determined until the home is built, and because the easiest time to install a radon mitigation system is during initial construction, the best practice recommendation is to install a passive ventilation stack in all new homes, with an electric outlet located in the attic near the vent stack so that it is available to power an in-line fan should post-construction testing dictate that an active radon system is needed to lower radon levels in the home. For more information, see Vertical Radon Ventilation Pipe.

    The first step in keeping radon and other soil gases out of the home is to install a continuous vapor barrier under the slab or over the crawlspace floor, and to perform thorough air sealing of floors and below-grade walls. See the following guides for more information on air sealing and vapor barriers for basements and crawlspaces.

    Because no vapor barrier is 100% foolproof, a passive or active radon mitigation system should be installed. The easiest time to install this is when the house is under construction, and the sub-slab gravel pad can be easily accessed to lay down a radon collection mat or pipe along the interior perimeter of the home. When this mat or pipe is attached to a vertical vent pipe which extends out through the roof, a negative pressure is created in the pipe, either actively via an in-line fan or passively due to the stack effect. This negative pressure draws soil gases up and out of the house.  

    How to Install a Radon Fan – Slab-on-Grade Construction

    1. Select the location for the ventilation pipe (min. 3” in dia.). It should be installed in a vertical run through a warm part of the house and exhausted through the roof. See Figure 1. The pipe should discharge at least 2 feet above the roof and 10 feet away from any openings in the building to keep the soil gas from re-entering the building.
    2. Lay a min. 3-inch-diameter perforated pipe in a gravel trench or a collection mat on top of the gravel around the interior side of the foundation perimeter. Install the pipe in a loop and connect the ends to each side of a vertical “T” pipe connector. The perforated pipe should loop through all sub-slab areas; multiple connection points or interconnections may be required.
    3. Place the polyethylene vapor barrier and concrete slab around the vertical “T”; label and cover the open top of the vertical “T” before placing the concrete. Seal the perimeter of the “T” to the concrete to reduce soil gas entry.
    4. Install the vertical pipe by connecting it to the vertical “T.” Avoid 90-degree angles in the vertical portion of the pipe; use sweeps if turns are needed. Label the pipe on each floor so it is clear the pipe is not part of the sewer system.  If the ventilation pipe extends through an unconditioned attic, insulate the stack to control condensation in the pipe.
    5. Run the pipe through the roof and flash it properly.  Provide a screened rain cap at the termination to prevent rain entry and nesting animals.
    6. Install an electrical junction box for powering the fan and add the fan to the vertical pipe run.
    Radon fan, slab-on-grade construction.
    Figure 1. Radon fan - slab-on-grade construction. (Source: Building Science Corporation.)

     

    How to Install a Radon Fan – Crawlspace Construction

    1. Select the location for the ventilation pipe (min. 3” in dia.). It should be installed in a vertical run through a warm part of the house and exhausted through the roof.  The pipe discharge should be installed at least 2’ above the roof and 10’ away from any openings in the building to keep the soil gas from re-entering the building.
    2. Lay at least 5’ of min. 3” diameter horizontal perforated pipe on the soil at the location where you will run the vertical ventilation pipe and connect it to either side of a vertical “T”. See Figure 2.
    3. Install a continuous layer of polyethylene vapor barrier with joints taped over the soil.  Run the polyethylene sheet up the wall and mechanically attach and seal the edges to the wall.  Seal the vertical “T” to the polyethylene to reduce the soil gas entry.
    4. Install the vertical pipe by connecting it to the vertical “T.” Avoid 90-degree angles in the vertical portion of the pipe; use sweeps if turns are needed.  Label the pipe on each floor so it is clear the pipe is not part of the sewer system.  If the ventilation pipe extends through an unconditioned attic, insulate the stack to control condensation in the pipe.
    5. Run the pipe through the roof and flash it properly.  Provide a screened rain cap at the termination to prevent rain entry and nesting animals.
    6. Install an electrical junction box for powering the fan and add the fan to the vertical pipe run.
    Radon fan - crawlspace construction.
    Figure 2. Radon fan - crawlspace construction. (Source: Building Science Corporation.)

     

    How to Install Radon Fan – Basement Construction

    1. Select the location for the ventilation pipe (min. 3” in dia.). It should be installed in a vertical run through a warm part of the house and exhausted through the roof.  The pipe discharge should be installed at least 2’ above the roof and 10’ away from any openings in the building to keep the soil gas from re-entering the building.
    2. Lay a min. 3” diameter perforated pipe in a gravel trench or a collection mat on top of the gravel around the foundation perimeter.  Install the pipe in a loop to allow for the soil gas to enter the pipe from two sides and connect it to either side of a vertical “T”.  Communication to all sub-slab areas is required and multiple connection points or interconnections may be required. See Figure 3.
    3. Place the polyethylene vapor barrier and concrete slab around the vertical “T”; label and cover the open top of the vertical “T” before placing the concrete.  Seal the perimeter of the “T” to the concrete to reduce the soil gas entry.
    4. Install the vertical pipe by connecting it to the vertical “T.” Avoid 90-degree angles in the vertical portion of the pipe; use sweeps if turns are needed.  Label the pipe on each floor so it is clear the pipe is not part of the sewer system.  If the ventilation pipe extends through an unconditioned attic, insulate the stack to control condensation in the pipe.
    5. Run the pipe through the roof and flash it properly.  Provide a screened rain cap at the termination to prevent rain entry and nesting animals.
    6. Install an electrical junction box for powering the fan and add the fan to the vertical pipe run.
    Radon fan - basement construction.
    Figure 3. Radon fan - basement construction. (Source: Building Science Corporation.)

     

    How to Install Vertical Ventilation Pipe – Retrofit Basement Construction

    1. Select the location for the ventilation pipe to be installed in a vertical run through a warm part of the house and exhausted through the roof.  The pipe discharge should be installed at least 2’ above the roof and 10’ away from any openings in the building to keep the soil gas from re-entering the building.
    2. Lay down the drainage mesh over the existing concrete slab to create a soil gas collection space.  Place an inverted toilet flange at the selected location and secure it to the slab.
    3. Place the polyethylene vapor barrier over the drainage mesh and seal it to the flange with sealant and tape.
    4. Install rigid foam insulation over the polyethylene and seal the gap between the insulation and the flange with expanding foam.  Lay down the subfloor over the insulation.  Insulation under the slab is not required by the building code; therefore, it is up to the homeowner to decide whether or not insulating the slab should be part of the retrofit.  Types of rigid insulation appropriate for this use include extruded polystyrene (XPS) and expanded polystyrene (EPS). See Figure 4.
    5. Install the vertical pipe by cementing it to the flange. Avoid using 90-degree angles in the vertical portion of the pipe; use sweeps if turns are needed.  Label the pipe on each floor so it is clear the pipe is not part of the sewer system.  If the ventilation pipe extends through an unconditioned attic, insulate the stack to control condensation in the pipe. See Figure 5.
    6. Run the pipe through the roof and flash it properly.  Provide a screened rain cap at the termination to prevent rain entry and nesting animals.
    7. Install an electrical junction box for powering the fan and add the fan to the vertical pipe run.
    Radon fan - retrofit basement construction.
    Figure 4. Radon fan - retrofit basement construction. (Source: Building Science Corporation.)

     

    Detail showing connection of a radon vent stack to an existing basement slab.
    Figure 5. Detail showing connection of a radon vent stack to an existing basement slab. (Source: Building Science Corporation.)

     

    Success
    Ensuring Success

    The home can be tested with a short-term or a long-term radon test kit that can be obtained through the mail or at local hardware stores. The short-term tests remain in the home between 2 and 90 days and the long-term tests remain for longer than 90 days. If the radon level is higher than 4 picocuries per liter of air (pCi/L) the radon mitigation fan should be installed and activated. The installation instructions for the radon mitigation system should be followed carefully as improper installation of the system can actually increase radon levels in a home.

    Climate
    Climate

    In cold climates, the vertical ventilation pipe should be located inside a heated space.  The vertical ventilation pipe should not be placed in an exterior wall as it will reduce the natural thermal stack effect and may prohibit the installation of the fan in the future.

    In hot climates, the wind, a hot attic, or heat from the sun could all impact the effectiveness of a passive vent stack.

    EPA recommends that the radon mitigation system be installed in high radon potential areas (Zone 1).  The list of Zone 1 counties can be found on the EPA website.

    EPA Radon Zone Map.
    EPA Radon Zone Map.

     

    Training
    Right and Wrong Images
    Image
    Wrong - Radon fan installed in the basement
    Wrong - Radon fan installed in the basement
    Image
    Radon fan– slab-on-grade construction
    Radon fan– slab-on-grade construction
    Image
    Right – The passive radon vent stack is properly labeled; this pipe brings radon and soil gases collected via a perforated pipe located under the floor slab up through an exterior wall for venting out through the roof.
    Right – The passive radon vent stack is properly labeled; this pipe brings radon and soil gases collected via a perforated pipe located under the floor slab up through an exterior wall for venting out through the roof.
    Presentations
    Author(s)
    Nicklas
    Organization(s)
    Huntsman Building Solutions
    Publication Date
    Description
    Webinar that talks about the dangers of radon gas and some solutions to keep a healthy indoor air environment. Free EBBA Digital Chalkboard Account required to view.
    Compliance

    Compliance

    The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

     

    ENERGY STAR Single-Family New Homes, Version 3/3.1 (Rev. 11)

    National Water Management System Builder Requirements

    Footnote 5) ... To earn the ENERGY STAR, EPA recommends, but does not require, that radon-resistant features be included in homes built in EPA Radon Zones 1, 2 & 3. For more information, see www.epa.gov/indoorairplus

     

    DOE Zero Energy Ready Home (Revision 07)

    Exhibit 1 Mandatory Requirements.
    Exhibit 1, Item 1) Certified under the ENERGY STAR Qualified Homes Program or the ENERGY STAR Multifamily New Construction Program.
    Exhibit 1, Item 6) Certified under EPA Indoor airPLUS.

     

    EPA Indoor airPLUS (Revision 04)

    2.1 Radon-Resistant Construction. Construct homes in EPA Radon Zone 1 with radon-resistant features (a passive system at minimum). EPA recommends that radon-resistant features are installed according to ANSI/AARST CCAH for 1-2 family dwellings and townhouses (max. total foundation area of 2500 sq. ft.) OR ANSI/AARST CC-1000 for larger foundations.

    Visually verify the following requirements:

    • Capillary break installed according to Specification 1.2, irrespective of climate zone.
    • A 3 or 4 in. diameter gas-tight vertical vent pipe, clearly labeled as a component of a radon reduction system. The vent pipe shall be connected to an open T-fitting in the aggregate layer (or connected to geotextile drainage matting according to the manufacturer’s instructions) beneath the polyethylene sheeting, extending up through the conditioned spaces and terminating a minimum of 12 in. above the roof opening. At least 10 ft. of horizontal perforated drain tile is to be attached to the T-fitting beneath the polyethylene sheeting placed over earthen crawlspaces and below concrete slabs. Note: suction points are not permitted on sump lids.
    • Radon fan (i.e., an active system) OR an electrical receptacle installed in an accessible attic location near the radon vent pipe (i.e., a passive system) to facilitate future fan installation if needed. A space surrounding the radon pipe, having a vertical height of not less than 48 inches and a diameter of not less than 21 inches, shall be provided in the attic area where the radon fan can be installed, if required.
    • Homes with no accessible attic location for a fan must utilize another exterior location or a garage that is not below conditioned space per ANSI/AARST CCAH. The branch circuit supply shall be labeled at the electrical panel indicating its intended use.
    • Foundation air sealing with polyurethane caulk or the equivalent at all slab openings, penetrations and control or expansion joints.

    Note: Larger buildings and multifamily properties may share mitigation systems across multiple units or may require multiple soil gas vent systems to accommodate large building footprints. See ANSI/AARST CC-1000 for electric metering requirements in shared (collateral) mitigation systems, as well as for maximum nominal sizes of soil gas collection plenums and corresponding pipe sizes.

    Note: Consult local building codes to determine whether additional radon requirements apply. Also consult EPA's "Building Radon Out" (EPA 402-K-01-002) for general guidance on installing radon-resistant features.

    Advisories:

    1. Elevated levels of radon have been found in homes built in all three zones on EPA’s Map of Radon Zones. Consult your state radon program for current information about radon in your area. Go to EPA's radon website and click on your state for contact information.
    2. EPA recommends, but does not require, that all homes built with radon-resistant features in EPA Radon Zone 1 include a radon vent fan. EPA also recommends radon-resistant features for homes built in EPA Radon Zones 2 and 3, and that all homes with or without radon-resistant features be tested for radon prior to occupancy. A radon vent fan should be installed when the test result is 4 pCi/L (the EPA action level) or more.
    3. Provide buyers with EPA’s Citizen’s Guide to Radon, encourage them to test for radon and refer them to EPA's radon website for more information.
    4. If soil or groundwater contamination is suspected on or near the building site (e.g., former industrial sites), volatile chemical contaminants from soil gas or vapor intrusion into a building may pose an IAQ risk. In such cases, EPA recommends radon-resistant features consistent with Specification 2.1, which can minimize or prevent the vapor intrusion into a house. See the EPA Vapor Intrusion Primer or ASTM E2600 for more information. You should also consult your state, tribal, or local environmental regulatory agency for information on the location of contaminated sites, including those subject to Superfund (CERCLA), Resource Conservation and Recovery Act (RCRA) cleanup requirements, or the Brownfields program. Visit EPA’s “Where You Live” for more information.

    See Indoor airPLUS Specifications for exceptions and for an alternative path for gut rehabs. 

     

    American Society for Testing Materials (ASTM)

    ASTM E1465–08a: Standard Practice for Radon Control Options for the Design and Construction of New Low-Rise Residential Buildings

    This practice provides the design details and construction methods for two built-in soil depressurization radon control and reduction systems appropriate for use in new low-rise residential buildings. Depending on the configuration of the radon vent stack installed, the radon system's operation may have a pipe route appropriate for a fan-powered radon reduction system, or have a more efficient pipe route appropriate for passively operated radon reduction systems. This practice covers special features for soil depressurization radon reduction systems including (1) slab-on-grade, basement and crawlspace foundation types with cast concrete slab and membrane ground covers, (2) sub-slab and sub-membrane gas-permeable layers and their drainage, (3) radon system piping, (4) radon discharge separation from openings into occupiable space, (5) radon fan installation, (6) electrical requirements, (7) radon system monitor installation, (8) labeling, (9) radon testing, and (10) system documentation.

    Retrofit
    Existing Homes

    SCOPE

    If radon testing indicates that radon concentrations inside an existing home with a passive vertical radon ventilation pipe reach or exceed 4 picocuries per liter (4 pCl), a radon fan shall be added to the vent system to prevent the accumulation of radon and soil gasses in the home. See the Scope and Description tab of this guide to learn more about why, where, and how this fan can be installed. This step should be taken in conjunction with other basement or crawlspace air sealing measures to help keep radon out of the home.

    If installation of the radon fan involves the movement and cutting of existing home components, see the Pre-Retrofit Assessment of Hazardous Materials as it relates to asbestos, VOCs, lead, and safe work conditions.

    If combustion appliances are located within the conditioned space of the home, see the Pre-Retrofit Assessment of Combustion Appliances.

    To help maintain a moisture control plan and to promote a safe living and work environment during the installation of the ventilation pipe, see the Pre-Retrofit Assessment of Crawlspaces and Basements.

    All retrofit radon reduction systems shall follow ASTM Designation E2121 – 13:  Standard Practice for Installing Radon Mitigation Systems in Existing Low-rise Residential Buildings. This standard is available for sale from ASTM.

    Radon guidance from EPA, HUD, NIH, OSHA, and FEMA can be found in Homeowner's and Renter's Guide to Reducing Radon After Disasters and Radon: Worker and Employer Guide to Hazards and Recommended Controls

    For more information, see the U.S. Department of Energy’s Standard Work Specifications regarding radon.

    Additional guidance and resources can be found in the Compliance tab and More tab of this guide.

    DESCRIPTION

    The steps for installing a radon exhaust fan in existing homes are similar to the steps included in the Description tab for new homes. The vertical vent pipe that the fan is attached to can be run through the warm part of the house or through a rim or band joist and up an exterior wall, or through a garage or unconditioned space and up through the roof. See the guide vertical radon ventilation pipes for more information. All retrofit radon reduction systems shall follow ASTM Designation E2121-13: Standard Practice for Installing Radon Mitigation Systems in Existing Low-Rise Residential Buildings. This standard is available for sale from ASTM

    In addition to installing an active or passive radon ventilation system, another important aspect of keeping soil gases out of a home is to provide a complete vapor barrier under the slab or over the crawlspace floor and to perform thorough air sealing of the floor and below-grade walls. See the Description tab and use the search mechanism to find specific Solution Center guides that will help with insulating, air sealing, and flashing specific parts of the house.

    COMPLIANCE

    ASTM E2121–13: Standard Practice for Installing Radon Mitigation Systems in Existing Low-Rise Residential Buildings.

    This practice describes methods for reducing radon entry into existing attached and detached residential buildings three stories or less in height. This practice is intended to provide radon mitigation contractors with a uniform set of practices. The methods described in this practice apply to currently occupied or formerly occupied residential buildings.

    More

    More Info.

    Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

    References and Resources*
    Author(s)
    Lstiburek Joseph W
    Organization(s)
    Building Science Corporation,
    BSC
    Publication Date
    Description
    Book presenting the best techniques for energy and resource efficient residential construction in the colder climates of North America.
    Author(s)
    Neuhauser Ken,
    Gates Cathy,
    Pettit Betsy
    Organization(s)
    Building Science Corporation,
    BSC
    Publication Date
    Description
    Guidebook providing useful examples of high performance retrofit techniques for the building enclosure of wood frame residential construction in a cold and somewhat wet climate.
    Author(s)
    U.S. Environmental Protection Agency
    Organization(s)
    EPA
    Publication Date
    Description
    Document outlining specifications that were developed by the U.S. Environmental Protection Agency (EPA) to recognize new homes equipped with a comprehensive set of indoor air quality (IAQ) features.
    Author(s)
    U.S. Environmental Protection Agency,
    Federal Emergency Management Agency,
    U.S. Department of Housing and Urban Development
    Organization(s)
    EPA,
    FEMA,
    HUD
    Publication Date
    Description
    Homeowner guidance from EPA, FEMA, HUD, and NIH on dealing with radon following a natural disaster.
    Author(s)
    U.S. Environmental Protection Agency,
    U.S. Department of Housing and Urban Development,
    National Institute of Health Division of Technical Resources,
    Occupational Safety and Health Administration
    Organization(s)
    EPA,
    HUD,
    NIH,
    OSHA
    Publication Date
    Description
    Worker guidance from EPA, HUD, NIH, and OSHA for radon issues following a natural disaster.
    *For non-dated media, such as websites, the date listed is the date accessed.
    Contributors to this Guide

    The following authors and organizations contributed to the content in this Guide.

    Sales
    Building Science Measures
    Building Science-to-Sales Translator

    Radon Resistant Construction =

    Image(s)
    Technical Description

    Radon is an odorless, colorless radioactive gas naturally occurring in the earth that can cause lung cancer in humans. It can enter homes through foundations and basements unless steps are taken to prevent it. Radon-resistant homes help minimize this risk by including a radon barrier with a fully sealed foundation and plastic sheet or layer of rigid-foam insulation rated for soil contact carefully taped at the seams under the slab or lining a crawl space. Below the radon barrier, a perforated pipe is laid in a 4-inch layer of crushed rock to collect radon and soil gasses and passively vent them through a solid vent pipe that goes up through the house (concealed inside a wall) and vents out through the roof. An electric junction box is installed in the attic near the vent pipe to power an inline fan to turn this passive venting system into an active system in case the radon is not being adequately exhausted through the passive exhaust pipe.


    Sales Message
    Last Updated

    Did you find this information helpful?

    If you have questions and/or would like a reply to this feedback, please include your e-mail address in the message.
    This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.