Active SSD System Materials and Installation Details

As can be seen in Figure 31.13, active SSD systems consist chiefly of a pipe system and a fan. There are several other components that should be included in a good system, but are not necessary to make the system reduce radon concentrations.

Most builders use 4 in. schedule 20 PVC pipes. Other sizes can be used but 4-in. PVC is readily available and is commonly used by builders for other purposes. Fans made for use in subslab systems are available in a variety of sizes from many vendors. The fans normally used are rated in a range of 90-150 cfm at no static pressure. Manufacturers of fans used for radon reduction are fairly quick to improve their products on advice from the people who are using their products. When the radon industry first started, many of the fans leaked at seams and joints, and required disassembly of the fan to seal those openings. Most manufacturers now supply fans that do not leak, but builders should be aware that this problem did exist and may still exist in some fans.

Additional materials and components that are normally included in a system satisfy safety needs, system performance indications, and common sense. Service switches should be placed within view of the fan to ensure that the system will not be activated while maintenance is in progress. Systems should be clearly marked as a radon reduction device to ensure that future owners of the building do not remove or destroy the system. An operation manual describing the system and its purpose should be made available.

Flashing

Service switch

Sewage line couplers

Flashing

Centrifugal fan

Service switch

Sewage line couplers

Alarm system

Identifica label

Identifica label

4 in. crushed gravel D.O.T.

FIGURE 31.13 Typical SSD system. (Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.)

4 in. crushed gravel D.O.T.

FIGURE 31.13 Typical SSD system. (Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.)

Some types of devices should be included in the system to advise the owners on system performance. These devices may be simple pressure gauges that tap into the pipe and measure and display the pressure in the exhaust pipe. A visual check of the gauge will alert the homeowner to possible system malfunctions. Electronic pressure-sensing devices that illuminate a warning light or sound an audible alarm when a pressure drop occurs are also used but they cost more than a simple gauge indicator. It is advisable to use a device that warns of a pressure change rather than something that warns that the fan is not running, because there are several things that can stop a system from operating effectively but that do not affect the fan.

Rain caps at the end of the pipe are intended to keep rain from entering the system. Builders use various cap designs for this purpose. The use of rain caps can cause a loss of airflow in a system, which may lessen the effectiveness of the system. It is advisable to use a rain cap that is designed in such a way as to not seriously impede airflow. For more information on rain caps and stack design, see the ASHRAE Fundamentals Handbook.19

Attention to detail during the installation process will help ensure the proper operation and long life of the system. Starting at the floor slab, seal the void between the pipe and the floor slab with a nonshrink grout or a flexible, highly adhesive sealant. Place a sticker or other labeling device on the pipe identifying the pipe as belonging to a radon reduction system. Ideally, a label should be placed at regular intervals along the entire pipe run. A visual system performance monitoring device should be placed in an area that is often visited and in plain view of the homeowner. Audible alarms can be placed in any area, as long as the homeowner can hear them. It is a good idea to place alarm sensors in easily accessible areas because they sometimes need adjusting. Run the pipe as straight as possible to the attic to ensure proper draining of condensation. The fan should always be located in a nonliving area as close to the exhaust as possible. This is extremely important because a leak in the fan or in the piping above the fan will blow the radon back out of the pipe. If the fan is placed in the basement, and a pipe leak occurs above the fan, radon-laden air will be introduced into the living area, and can cause radon levels to build to very high concentrations. Most builders connect the fans to the pipe system with rubber sewage pipe connectors. This allows for the easy removal and replacement of the fan if that should become necessary. Always install a service switch in sight of the fan. Run the pipe through the roof and flash well. If desired, cap the pipe with a rain cap.

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