What Is Passive Radon Mitigation?

On this page (8 sections)

1. What is passive radon mitigation made of?
2. How does a passive radon system work?
3. What is the difference between passive and active radon mitigation?
4. When should you add a fan?
5. Which pipe should a passive radon system use?
6. What should you monitor after installation?
7. Is hearing protection useful during fan installation?
8. How do you decide between passive and active mitigation?

Passive radon mitigation uses a sealed pipe route to move soil gas from beneath a building to the outdoors without a continuously running fan. The system relies on natural pressure differences and temperature-driven airflow, so testing is the only way to know whether it lowers indoor radon enough.

Passive systems are common in new construction, where the pipe and suction point can be built into the foundation. An existing passive system may also be upgraded with a fan if follow-up testing shows that natural airflow is not enough.

What is passive radon mitigation made of?

A passive radon mitigation system usually has a suction point, sealed piping, and an outdoor discharge point above the roof. The suction point collects soil gas below or beside the foundation, while the pipe gives that gas a route out of the building.

For sub-slab material, see rock under a slab.

Common parts include:

• A cleared suction pit beneath a slab or in a crawlspace.
• A vertical pipe that runs through the building.
• Sealed joints and penetrations around the pipe.
• A discharge point above the roofline.
• A visible label or system marker.
• A test point that allows later fan installation or system checks.

The exact layout depends on the foundation and soil. Read our guide to how a passive radon system works in new construction for the planning choices that affect the pipe route and suction point.

A passive system is different from an active system because it has no powered fan creating steady suction. The pipe still needs a clear route, sealed connections, and a discharge location that does not send soil gas back toward windows, doors, or air intakes.

How does a passive radon system work?

Passive radon mitigation works by reducing the resistance between soil gas below the foundation and the outdoor air. Warm air rising through the vertical pipe can create a natural draft, while pressure differences between the soil, building, and outdoors help move gas upward.

The system also depends on the building envelope. Cracks, gaps, sump openings, crawlspace connections, and utility penetrations can allow soil gas into living areas before it reaches the suction point.

Sealing those openings is part of good radon work, but sealing alone may not solve the problem. Radon enters through many pathways, and the soil beneath a building can continue supplying gas.

The EPA's radon mitigation guidance explains why testing and proper system design matter. Results can change with weather, heating, ventilation, soil conditions, and how tightly a building is sealed.

Do passive radon systems work?

Passive radon systems can work, but their performance depends on the building, soil, foundation, and system design. A pipe that looks complete from the outside does not prove that indoor radon has been reduced.

Test before relying on the system, then test again after installation or major building changes. A long-term test can show the average exposure over time, while a continuous monitor can help you see changes during different conditions.

Our guide to do passive radon systems work covers the limits of natural airflow and the situations where a powered fan may be more suitable.

What is the difference between passive and active radon mitigation?

Passive mitigation uses natural airflow, while active mitigation adds a fan that creates mechanical suction. The fan increases airflow through the sub-slab route and can help overcome conditions that limit natural draft.

A passive system may be suitable when:

• It was designed into a new home.
• The pipe route is continuous and well sealed.
• The suction point matches the foundation design.
• Follow-up testing shows low indoor radon.
• There is a practical path for adding a fan later.

An active system may be considered when:

• Follow-up radon results remain high.
• The building has weak natural stack effect.
• The foundation or soil limits passive airflow.
• The pipe route has a long or complex path.
• A professional recommends steady sub-slab suction.

The choice is not based on the pipe alone. Compare the factors in passive vs active radon mitigation systems before changing an installed system.

When should you add a fan?

Add a radon fan only after checking the test results, pipe route, suction point, and discharge setup. A fan must match the system's airflow and resistance needs, and the installation must keep exhaust away from the building.

A fan can make a passive system active, but it does not correct every design problem. An unsealed joint, blocked pipe, poor suction pit, or unsuitable discharge point can still reduce performance.

Which fan can suit an upgrade?

The Festa AMG Maverick Radon Fan is a 260 CFM electric inline exhaust fan for a 4 in duct. Its title identifies a brushless motor, glass reinforced poly-resin construction, white color, and a cylindrical form, while the product information gives a power use of up to 70 watts and a 50–60 dB range.

Festa AMG Radon Fans describes this model as suitable for indoor and outdoor use and gives it a 5-year warranty against fan failure. The information also says it is not for use in unattended areas, so installation and placement deserve careful attention.

Its 4 in duct size matters when checking an existing passive route. Read the system measurements first, then confirm the fan, pipe, couplers, electrical connection, and discharge plan with a qualified installer.

Which pipe should a passive radon system use?

The pipe must provide a continuous, low-resistance route from the suction point to the outdoor discharge. Size, material, joint sealing, support, and the number of bends all affect how easily soil gas can move.

A pipe that is too small or sharply routed can restrict airflow. Poorly sealed joints can let radon escape into the building instead of carrying it outdoors.

Use the guidance in which pipe should you use for a passive radon system when reviewing pipe material and layout. The right pipe choice depends on the foundation, route, climate, and whether a future fan is planned.

What should you monitor after installation?

Test indoor radon after the passive system is installed and keep checking at sensible intervals. A passive vent pipe is a pathway, not a measurement of indoor air quality.

A radon monitor with an alarm can help you notice when readings rise above a chosen level. Read Radon Monitors with Alarm System: A Useful Guide if you want alerts alongside regular measurements.

A basic explanation of the instrument is in What Is a Radon Detector? A Simple Guide.

Place any detector or monitor according to its instructions, away from drafts, high heat, direct sun, and areas where it can be disturbed.

For an under-slab design, how an under-slab radon mitigation system works explains how the suction area beneath the foundation connects to the vent route.

Is hearing protection useful during fan installation?

The Walker's Walker's Razor Slim Passive Earmuff is a compact passive earmuff designed for youth and women shooters. It has a slim profile, ultra-low-profile ear cups with a rubberized coating, a metal wire frame in the headband, a collapsible design, and a 27 dB Noise Reduction Rating.

This product is hearing protection, not a radon component. It may suit someone who needs a foldable option for a loud work area, but it does not measure radon, seal pipe joints, or create suction.

Use hearing protection according to its instructions and keep it separate from the system's safety checks. Radon work still requires attention to electrical safety, roof access, ventilation, and the building's discharge route.

How do you decide between passive and active mitigation?

Keep a passive system when testing shows that it controls indoor radon and the installation is sound. Consider a fan upgrade when readings remain high or the system's natural airflow is too weak for the building.

Start with testing, inspect the pipe and seals, and check the suction point and discharge location. If you add a fan, retest after installation and keep records of the results.

The simple decision rule is this: passive radon mitigation may be enough when the system is well designed and test results are low. Choose an active upgrade when measured radon remains high and a compatible fan can be installed safely into the existing route.

Frequently asked questions

What is passive radon mitigation?

Passive radon mitigation is a radon reduction system that uses a sealed pipe, a suction point beneath the slab, and natural air movement to route soil gas outdoors. It has no continuously operating fan, so testing is needed to confirm whether the system reduces indoor radon to an acceptable level.

Does passive radon mitigation use electricity?

No. A passive system does not use an electric fan during normal operation.

It depends on pressure differences, temperature changes, and the open vent path to move soil gas.

If results remain high, a qualified professional may recommend adding a fan and electrical connection.

Can a passive radon system be upgraded?

Often, a passive radon system can be upgraded by adding an inline fan to the vent route, but the pipe layout, suction point, discharge location, and electrical setup must be checked first. Retest after any change to confirm that indoor radon levels have fallen.

How do you know if passive radon mitigation is working?

Use a radon test or monitor after the system is installed and again after major changes. A vent pipe alone does not prove that indoor radon is low.

The EPA recommends testing homes because radon levels vary by building, soil, weather, and ventilation conditions.