Radon guide

How a radon mitigation system works

Radon rises from the soil and is drawn into a house through cracks, joints and gaps around pipes, because air pressure indoors is usually a little lower than in the ground. Most mitigation systems turn that around: they lower the pressure under the foundation so the gas goes up a pipe instead of into the rooms.

Cross-section of a house with a sub-slab suction system: a pipe runs from a hole in the basement floor up through the house to a fan in the attic and vents above the roof. Fan in attic or outside wall Exhaust above roof Sealed basement floor Radon in the soil Suction pipe
Sub-slab suction, the most common setup. Drawing simplified; pipe routes vary by house.

The methods, by foundation

Sub-slab suctionFor basements and slabs. One or more pipes go through the floor into the gravel or soil beneath; a fan pulls the gas out. EPA lists 50 to 99% reduction.
Drain tile and sump suctionUses existing drain tile or a sump pit as the collection point, which can save drilling. Also 50 to 99%.
Crawlspace membraneHeavy plastic sheeting covers the crawlspace soil and a pipe draws radon from underneath it. 50 to 99%, with less heat loss than venting the crawlspace.
Pressurizing or ventilatingRaising basement air pressure or bringing in outdoor air. Results vary and heating or cooling losses can be large, so these are used where suction does not fit.

Sealing cracks and openings helps the other methods work but does not lower radon much on its own; EPA treats it as a supporting step. Homes on a private well can also have radon in the water, which is treated separately with aeration (95 to 99%) or a carbon filter (85 to 95%).

What a correct installation looks like

  • The exhaust leaves above the roof surface, at least 10 feet above the ground and well away from windows and doors, so the gas cannot drift back in.
  • The fan sits outside living space: EPA lists attics, garages and other unconditioned spaces, or the outside of the house.
  • The system is clearly labeled, so nobody changes it by accident.
  • A warning device shows the system is running: a liquid gauge, a light, a sound alarm or a dial.

After it is installed

  1. Test again within 30 days. Wait at least 24 hours after the fan starts. EPA recommends an independent test even if the contractor runs one.
  2. Leave the fan on. It has to run continuously; switching it off brings the radon back.
  3. Glance at the gauge now and then. If it shows a problem, call the contractor.
  4. Retest at least every two years and after remodeling, especially if a lower floor becomes living space.

Wondering about price? See what mitigation costs.

Sources: EPA, Consumer's Guide to Radon Reduction (2016); EPA, A Citizen's Guide to Radon (2016). Updated October 2026.

More radon guides

How to test your home for radonKits, placement and how long to leave themWhat is a safe radon level?Read your result against EPA's numbersRadon mitigation costWhat official sources say and what drives a quoteRadon health risksLung cancer risk by level, smokers and non-smokersRadon when buying or selling a homeTesting options during a sale and what to ask