What to Look for in a Radon Reduction System
In selecting a radon reduction method for your home, you and your contractor should consider several things, including: how high your initial radon level is, the costs of installation and system operation, your home size, and your foundation type.
Installation and Operating Costs
Most types of radon reduction systems cause some loss of heated or air conditioned air, which could increase your utility bills. How much your utility bills will increase will depend on the climate you live in, what kind of reduction system you select, and how your home is built. Systems that use fans are more effective in reducing radon levels; however, they will slightly increase your electric bill.
Radon Reduction Techniques
There are several methods a contractor can use to lower radon levels in your home. Some techniques prevent radon from entering your home while others reduce radon levels after it has entered. EPA generally recommends methods which prevent the entry of radon. Soil suction, for example, prevents radon from entering your home by drawing the radon from below the home and venting it through a pipe, or pipes, to the air above the home where it is quickly diluted.
Any information that you may have about the construction of your home could help your contractor choose the best system. Your contractor will perform a visual inspection of your home and design a system that considers specific features of your home. If this inspection fails to provide enough information, the contractor will need to perform diagnostic tests during the initial phase of the installation to help develop the best radon reduction system for your home. For instance, your contractor can use chemical smoke to find the source and direction of air movement. A contractor can learn air flow sources and directions by watching a small amount of smoke that he or she shot into holes, drains, sumps, or along cracks. The sources of air flow show possible radon routes. A contractor may have concerns about backdrafting of combustion appliances when considering radon mitigation options, and may recommend that the homeowner have the appliances checked by a qualified inspector.
Another type of diagnostic test is a soil communication test. This test uses a vacuum cleaner and chemical smoke to determine how easily air can move from one point to another under the foundation. By inserting a vacuum cleaner hose in one small hole and using chemical smoke in a second small hole, a contractor can see if the smoke is pulled down into the second hole by the force of the vacuum cleaner's suction. Watching the smoke during a soil communication test helps a contractor decide if certain radon reduction systems would work well in your home.
Whether diagnostic tests are needed is decided by details specific to your home, such as the foundation design, what kind of material is under your home, and by the contractor's experience with similar homes and similar radon test results.
Home Foundation Types
Your home type will affect the kind of radon reduction system that will work best. Homes are generally categorized according to their foundation design. For example: basement, slab-on-grade, concrete poured at ground level; or crawlspace, a shallow unfinished space under the first floor. Some homes have more than one foundation design feature. For instance, it is common to have a basement under part of the home and to have a slab-on-grade or crawlspace under the rest of the home. In these situations a combination of radon reduction techniques may be needed to reduce radon levels to below 4 pCi/L.
Radon reduction systems can be grouped by home foundation design. Find your type of foundation design above and read about which radon reduction systems may be best for your home.
Basement and Slab-on-Grade Homes
In homes that have a basement or a slab-on-grade foundation, radon is usually reduced by one of four types of soil suction: subslab suction, drain-tile suction, sump-hole suction, or block-wall suction.
Active Subslab suction — also called subslab depressurization — is the most common and usually the most reliable radon reduction method. One or more suction pipes are inserted through the floor slab into the crushed rock or soil underneath. They also may be inserted below the concrete slab from outside the home. The number and location of suction pipes that are needed depends on how easily air can move in the crushed rock or soil under the slab and on the strength of the radon source. Often, only a single suction point is needed.
A contractor usually gets this information from visual inspection, from diagnostic tests, and/or from experience. A radon vent fan connected to the suction pipes draws the radon gas from below the home and releases it into the outdoor air while simultaneously creating a negative pressure or vacuum beneath the slab. Common fan locations include unconditioned home and garage spaces, including attics, and the exterior of the home.
Passive subslab suction is the same as active subslab suction except it relies on natural pressure differentials and air currents instead of a fan to draw radon up from below the home. Passive subslab suction is usually associated with radon-resistant features installed in newly constructed homes. Passive subslab suction is generally not as effective in reducing high radon levels as active subslab suction.
Some homes have drain tiles or perforated pipe to direct water away from the foundation of the home. Suction on these tiles or pipes is often effective in reducing radon levels.
One variation of subslab and drain tile suction is sump-hole suction. Often, when a home with a basement has a sump pump to remove unwanted water, the sump can be capped so that it can continue to drain water and serve as the location for a radon suction pipe.
Block-wall suction can be used in basement homes with hollow block foundation walls. This method removes radon and depressurizes the block wall, similar to subslab suction. This method is often used in combination with subslab suction.
An effective method to reduce radon levels in crawlspace homes involves covering the earth floor with a high-density plastic sheet. A vent pipe and fan are used to draw the radon from under the sheet and vent it to the outdoors. This form of soil suction is called submembrane suction, and when properly applied is the most effective way to reduce radon levels in crawlspace homes. Another less-favorable option is active crawlspace depressurization which involves drawing air directly from the crawlspace using a fan. This technique generally does not work as well as submembrane suction and requires special attention to combustion appliance backdrafting and sealing the crawlspace from other portions of the home, and may also result in increased energy costs due to loss of conditioned air from the home.
In some cases, radon levels can be lowered by ventilating the crawlspace passively, or actively, with the use of a fan. Crawlspace ventilation may lower indoor radon levels both by reducing the home's suction on the soil and by diluting the radon beneath the home. Passive ventilation in a crawlspace is achieved by opening vents, or installing additional vents. Active ventilation uses a fan to blow air through the crawlspace instead of relying on natural air circulation. In colder climates, for either passive or active crawlspace ventilation, water pipes, sewer lines and appliances in the crawlspace may need to be insulated against the cold. These ventilation options could result in increased energy costs for the home.
Other Types of Radon Reduction Methods
Other radon reduction techniques that can be used in any type of home include: sealing, home or room pressurization, heat recovery ventilation and natural ventilation.
Sealing cracks and other openings in the foundation is a basic part of most approaches to radon reduction. Sealing the cracks limits the flow of radon into your home, thereby making other radon reduction techniques more effective and cost-efficient. It also reduces the loss of conditioned air. EPA does not recommend the use of sealing alone to reduce radon because, by itself, sealing has not been shown to lower radon levels significantly or consistently. It is difficult to identify and permanently seal the places where radon is entering. Normal settling of your home opens new entry routes and reopens old ones.
Home or room pressurization uses a fan to blow air into the basement, or living area from either upstairs or outdoors. It attempts to create enough pressure at the lowest level indoors — in a basement, for example — to prevent radon from entering into the home. The effectiveness of this technique is limited by home construction, climate, other appliances in the home and occupant lifestyle. In order to maintain enough pressure to keep radon out, the doors and windows at the lowest level must not be left opened, except for normal entry and exit. This approach generally results in more outdoor air being introduced into the home, which can cause moisture intrusion and energy penalties. Consequently, this technique should only be considered after the other, more-common techniques have not sufficiently reduced radon.
A heat recovery ventilator, or HRV, also called an air-to-air heat exchanger, can be installed to increase ventilation which will help reduce the radon levels in your home. An HRV will increase ventilation by introducing outdoor air while using the heated or cooled air being exhausted to warm or cool the incoming air. HRVs can be designed to ventilate all or part of your home, although they are more effective in reducing radon levels when used to ventilate only the basement. If properly balanced and maintained, they ensure a constant degree of ventilation throughout the year. HRVs also can improve air quality in homes that have other indoor pollutants. There could be significant increase in the heating and cooling costs with an HRV, but not as great as ventilation without heat recovery (see the "Radon Reduction of Various Mitigation Techniques").
Some natural ventilation occurs in all homes. By opening windows, doors, and vents on the lower floors you increase the ventilation in your home. This increase in ventilation mixes outdoor air with the indoor air containing radon, and can result in reduced radon levels. However, once windows, doors and vents are closed, radon concentrations most often return to previous values within about 12 hours. Natural ventilation in any type of home should normally be regarded as only a temporary radon reduction approach because of the following disadvantages: loss of conditioned air and related discomfort; greatly increased costs of conditioning additional outside air; and security concerns.
Source: United States Environmental Protection Agency
Photos: United States Environmental Protection Agency