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What filters radon?

By Radon411 Editorial TeamUpdated How we research

Short answer

For radon in indoor air, the recommended fix is not a filter: it keeps radon out, usually with a vent pipe and fan that pull it from under the house. For radon in well water, point-of-entry treatment works: a granular activated carbon filter typically removes 85 to 95 percent and aeration 95 to 99 percent.

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

Methods that prevent the entry of radon are generally recommended. The one primarily used is a vent pipe and fan that pulls radon from beneath the house and vents it outside, and some systems cut radon by up to 99 percent. Opening windows is only temporary, and sealing alone is not recommended.

Radon in well water is the case for a filter. Point-of-entry treatment removes radon before the water enters the home's pipes. GAC filters usually cost less and suit moderate levels, but can collect radioactivity and may need careful disposal; aeration is generally more efficient. A filter at a single tap treats only a small share of the water and does not address radon released into the air.

Measure before you buy anything: test the air first, and if you are on a private well, test the water too, since the devices and procedures for water differ from those for air.

What to do next: test the air first. If you are on a private well, have the water tested, and if either result is elevated, get quotes from certified professionals for the matching fix.

Radon in air is kept out, not filtered

For radon in indoor air, the recommended approach is to stop it getting in rather than to filter it once it is inside. Methods that prevent the entry of radon are generally recommended, and the one primarily used is a vent pipe and fan that pulls radon from beneath the house and vents it outside, where it is quickly diluted.

What actually removes radon, by where it is
Radon inWhat worksTypical reduction
Indoor airSoil suction: a vent pipe and fan under the houseSome systems up to 99 percent
Well waterAeration at the point of entry95 to 99 percent
Well waterGranular activated carbon (GAC) filter at the point of entry85 to 95 percent

Why air filtering is not the fix

Radon is a gas, and the harm comes from what it turns into: it decays into radon progeny, solid radioactive particles that can attach to dust and move with the air. The recommended approach deals with the gas at its source, keeping it out of the living space.

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 soil suction system draws radon from under the slab and vents it above the roof.

Ventilation can help a little but has limits. Opening windows is only a temporary approach, and a heat recovery ventilator has limited use, its effectiveness limited by the radon level and the ventilation air available. See does radon mitigation work.

Filters that do work: water treatment

Radon in well water is the case where a filter does the job. Point-of-entry treatment removes radon from the water before it enters the home's pipes, usually with a granular activated carbon filter or an aeration system.

Typical radon reduction, EPA

Radon in private well water

  • Private well water: aeration95 to 99 percentGenerally more efficient than GAC; requires annual cleaning to maintain effectiveness and to prevent contamination; requires venting radon to outdoors.
  • Private well water: granular activated carbon (GAC)85 to 95 percentLess efficient for higher levels than aeration; use for moderate levels, around 5,000 pCi/L or less in water.
Typical radon reduction for aeration and for granular activated carbon.
Carbon filter or aeration
FeatureGAC filterAeration
Typical reduction85 to 95 percent95 to 99 percent
Suited toModerate levels, around 5,000 pCi/L or less in waterHigher levels; generally more efficient
CostUsually lessUsually more
Watch forCollects radioactivity; may need shielding and careful disposalAnnual cleaning; radon vented outdoors

Tap filters fall short

A point-of-use filter at a single tap treats only a small portion of the water, such as the water you drink. Most of the risk from radon in water comes from radon released into the air when water is used for showering and other household purposes, and tap devices are not effective against that.

Test before you buy any filter

Measure first. Testing is the only way to know your radon level, and it is important to first test the air in the home. If the air shows a radon problem and your water comes from a well, have the water tested; the devices and procedures for water are different from those used for air. Radon entering through soil is usually a much larger risk than radon from water.

Test, then choose the fix
ResultFix
Air highA soil suction system
Well water highPoint-of-entry aeration or GAC
Both highBoth, air first

Questions about filtering radon

Does an air purifier remove radon?

Air cleaning is not the recommended fix. Methods that prevent radon from entering, such as a vent pipe and fan under the house, are generally recommended.

What filter removes radon from water?

A granular activated carbon filter at the point of entry typically removes 85 to 95 percent. Aeration typically removes 95 to 99 percent.

Does a pitcher or tap filter remove radon?

A point-of-use device treats only a small share of the water and is not effective against radon released into the air from all the water used in the home.

Do carbon filters become radioactive?

They can collect radioactivity and may need a radiation shield around the tank and care in disposal.

Does an HRV filter radon?

A heat recovery ventilator increases ventilation, which helps reduce radon, but its use is limited by the radon level and the ventilation air available.

Does opening windows clear radon out?

Only for a while. Once windows, doors and vents are closed, radon most often returns to previous values within about 12 hours.

Should I test water or air first?

Air first. Radon from soil is usually a much larger risk than radon from water.

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