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Does radon mitigation work?

By Radon411 Editorial TeamUpdated How we research

Short answer

Yes: some radon mitigation systems can cut the radon level in a home by up to 99 percent, and most homes can be brought to 2 pCi/L or below. The proof for your home is a follow-up test within 30 days of installation, with the fan running continuously after that.

Next step: a certified professional designs and installs the fix. Find a mitigation professional

Most systems use soil suction: a vent pipe and fan pull radon from beneath the house and vent it to the air above the home, where it is quickly diluted. Subslab suction, the most common and usually the most reliable method, typically lowers radon by 50 to 99 percent, and works best when air moves easily in the material under the slab.

How well a system works depends on its design and installation: the number and location of suction pipes, the sealing of cracks and openings, and a fan that runs continuously. Lowering high radon levels takes technical knowledge and special skills, so use a contractor trained to fix radon problems.

Shortcuts do not give the same result. Sealing alone has not been shown to lower radon levels significantly or consistently, and opening windows is only a temporary approach.

What to do next: if your test shows an elevated level, get more than one estimate from trained professionals, and book a follow-up test for within 30 days of the system going in.

How much radon mitigation lowers radon

Radon works. Some radon reduction systems can cut the level in a home by up to 99 percent, and radon levels can be reduced in most homes to 2 or below. How much a given system achieves depends on the method and on the home.

Typical radon reduction, EPA

Basement and slab-on-grade homes

  • Subslab suction (subslab depressurization)50 to 99 percentWorks best if air can move easily in material under slab.
  • Drain tile suction50 to 99 percentCan work with either partial or complete drain tile loops.
  • Block-wall suction50 to 99 percentOnly in homes with hollow block-walls; requires sealing of major openings.
  • Sump-hole suction50 to 99 percentWorks best if air moves easily to sump from under the slab.

Crawlspace homes

  • Submembrane depressurization in a crawlspace50 to 99 percentLess heat loss than natural ventilation in cold winter climates.
Typical radon reduction for each soil suction method, as ranges.

Each of the soil suction methods typically cuts radon by 50 to 99 percent. Subslab suction is the most common and usually the most reliable method, and it works best when air can move easily in the material under the slab.

Why soil suction works

Air pressure inside a home is usually lower than in the soil around its foundation, so the house acts like a vacuum and draws radon in through foundation cracks and other openings. A soil suction system turns that around: a vent pipe and fan pull radon from beneath the house and vent it through a pipe to the air above the home, where it is quickly diluted.

Cross-section of a house with a sub-slab depressurization system: soil gas drawn from beneath the slab into a suction point, up a vent pipe, through a fan outside the living space and out above the roofline.
Read this figure as text
Sub-slab depressurization system in a house cross-sectionGround levelLiving spaceBasement12345
  1. Soil gas drawn from beneath the slab
  2. Suction point through the slab
  3. Vent pipe
  4. Fan, outside the living space
  5. Discharge above the roofline
A sub-slab depressurization system: a suction point under the slab, a vent pipe, and a fan that exhausts above the roof.

Because it stops radon before it enters, rather than treating it after it gets in, this is the kind of method EPA generally recommends. These systems do not require major changes to the home, and sealing foundation cracks and other openings makes them more effective and cost-efficient. See how mitigation systems work.

What decides how well a system works

What makes a radon system work well
FactorWhy it matters
Air movement under the slabSubslab suction works best if air can move easily in the material under the slab
Number and placement of suction pipesSet by how easily air moves under the slab and by the strength of the radon source
SealingSealing cracks and openings makes the system more effective and cost-efficient
A fan that never stopsThe fan must run continuously for the system to work correctly
The installer's skillLowering high radon levels takes technical knowledge and special skills; without them, a level can even go up

That last row is why the installer matters: use a contractor trained to fix radon problems. Many states require radon professionals to be licensed, certified or registered, and it is wise to get more than one estimate. See find a mitigation professional.

How to know your system is working

The proof that a system works in your home is a test, not the installation. A test should be done within 30 days of installation, and an independent follow-up measurement is also recommended. To test the system's effectiveness, a two- to seven-day measurement is recommended.

Timeline after a radon mitigation system is installed: the fan runs continuously, test no sooner than 24 hours and within 30 days, then retest at least every two years.
Read this figure as text

  1. Day of installation

    The system goes in

    Keep the fan running at all times: it must run continuously for the system to work correctly.

  2. No sooner than 24 hours

    Earliest post-mitigation test

    Test no sooner than 24 hours after your system is in operation with the fan on, if it has one.

  3. Within 30 days

    Post-mitigation test done

    A two- to seven-day measurement is recommended, and EPA recommends an independent follow-up radon measurement as well as any test the contractor runs.

  4. At least every two years

    Retest

    Retest your home at least every two years to be sure radon levels remain low.

Test conditions: Windows and doors must be closed 12 hours before and during the test, except for normal entry and exit. Not drawn to scale.

After a remodel. After you remodel, retest in the lowest lived-in area to make sure the construction did not reduce the effectiveness of the radon reduction system.

Testing after a radon system goes in: the first check, then regular retests.

  1. Test after installation

    Within 30 days, and consider an independent follow-up measurement.

  2. Watch the warning device

    Every active system needs one. Look at it, usually a manometer, on a regular basis.

  3. Keep the fan on

    The fan should never be turned off; it must run continuously for the system to work correctly.

  4. Retest

    At least every two years, and in the lowest lived-in area after you remodel.

  5. Plan for the fan

    Like a furnace or chimney, the system needs occasional maintenance. Fans may last five years or more and may then need repair or replacement.

What does not work as well

Approaches that fall short of a radon system
ApproachWhat to expect
Sealing aloneNot recommended: by itself, sealing has not been shown to lower radon levels significantly or consistently, and normal settling opens new entry routes
Opening windowsOnly a temporary approach; once windows, doors and vents are closed, radon most often returns to previous values within about 12 hours
Switching the fan offThe system stops doing its job; the fan must run continuously
Untrained do-it-yourself workWithout the proper equipment or knowledge, you could increase your radon level or create other hazards and costs

See can radon be removed completely and do-it-yourself radon mitigation.

Questions about whether mitigation works

How effective is radon mitigation?

Some systems can reduce radon by up to 99 percent, and radon levels can be reduced in most homes to 2 pCi/L or below.

How long does a radon mitigation system last?

It needs occasional maintenance, like a furnace or chimney. Fans may last five years or more and may then need to be repaired or replaced.

When should I test after mitigation?

Within 30 days of installation, with a two- to seven-day measurement, and consider an independent follow-up measurement.

Can radon levels go back up after mitigation?

The fan must run continuously for the system to work, and remodeling can affect it, so retest at least every two years and in the lowest lived-in area after you remodel.

Does sealing cracks work on its own?

No. Sealing alone is not recommended, because by itself it has not been shown to lower radon levels significantly or consistently. It helps as part of a system.

Should the installer also do the follow-up test?

A potential conflict of interest exists when the same person or firm tests and installs the system. A test by an independent, qualified radon tester is recommended.

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