Radon Mitigation Fans: How They Work and How to Know Yours Is Running

A radon mitigation system is deceptively simple: a pipe running from beneath your slab or foundation membrane to the outside, with a fan creating continuous negative pressure that pulls radon gas out before it can accumulate inside. The fan is the heart of the system, and understanding how it works helps you maintain it properly.

How a Radon Mitigation Fan Works

The most common system—sub-slab depressurization (SSD)—works on a straightforward principle. The fan creates suction in the pipe, which draws air (and radon) from beneath the concrete slab. This slightly lowers the pressure below the slab relative to the interior of the house.

Because pressure moves from high to low, radon-containing soil air flows toward the suction point rather than through cracks in the foundation into the living space. The fan exhausts that air to the outside—typically through the roof or high on an exterior wall.

The system runs continuously. Radon mitigation fans are designed for 24/7 operation and are engineered for long service lives.

Types of Radon Mitigation Fans

Fans are selected based on the airflow and static pressure requirements of your specific foundation. Two key specifications matter:

Static pressure: The ability to maintain suction against resistance (soil density, long pipe runs). Measured in inches of water column (in. w.c.).

Airflow: Volume of air moved, measured in cubic feet per minute (CFM).

Dense, clay-heavy soils require high-pressure fans because sub-slab communication is poor—the fan needs to work harder to pull air through. Sandy, permeable soils need lower pressure but may require higher airflow.

Common residential radon fan brands include Radon Away (RP, GP, and GP Pro series), Festa (Radonfan series), and Fantech. A properly sized fan for your foundation is critical—an undersized fan won’t achieve adequate suction, and an oversized fan can depressurize the basement enough to cause backdrafting from combustion appliances.

The Manometer: Your System’s Indicator Light

Most radon mitigation systems include a U-tube manometer—a small, liquid-filled gauge mounted on the radon pipe. This is your visual indicator that the system is working.

When the fan is creating suction, the liquid in the manometer is pulled upward on the suction side of the pipe. A level difference between the two sides (typically 1–3 inches) indicates normal operation.

What to look for:

• Unequal levels = fan is running and creating suction ✓
• Equal levels (flat) = fan has stopped or is not creating suction ✗

Check your manometer monthly. It takes five seconds and tells you immediately whether your system is functioning.

Fan Alarm Options

Some systems include an electronic radon alarm or a continuous radon monitor that alerts you if levels rise above a set threshold. These are particularly useful for:

• Homes where the fan is in an inaccessible location
• Landlord-tenant situations where regular monitoring is important
• Homes with very young children or immunocompromised residents

Electronic alarms are typically separate from the fan itself and are mounted in the living space.

How Long Do Radon Fans Last?

Quality radon mitigation fans are built for continuous operation. Most last:

• Standard fans (RP/GP series): 5–10 years before replacement is common
• High-efficiency or premium fans: 10–15 years
• Lifespan factors: Humidity, pipe routing moisture, operating temperature

The fan motor is sealed, but moisture condensation inside the pipe can enter the motor housing over time—particularly in fans installed in unconditioned attic space with large temperature swings. This is the primary cause of fan failure.

Signs Your Fan Has Failed or Is Failing

Manometer shows level liquid. This is the clearest indicator—the suction is gone.

Unusual noise. New rattling, humming, or clicking from the fan or pipe can indicate bearing wear or debris in the fan housing.

Higher radon test results. If a retested home shows significantly elevated levels after having had a working system, fan failure is a top suspect.

Fan is warm to the touch at the housing. Excessive heat can indicate motor stress.

The fan has stopped audibly. Radon fans produce a low, constant hum—if you can’t hear it near the pipe, it may have stopped.

Fan Replacement

Replacing a radon fan is a straightforward job for a certified mitigator. It involves:

1. Disconnecting the power to the fan
2. Cutting the fan out of the pipe
3. Installing the new fan in the same location with the same pipe diameter
4. Restoring electrical connection

A new fan typically costs $150–$400 for the unit, and labor for replacement runs $100–$250 at most contractors. Total fan replacement cost: $250–$650 in most markets.

Some homeowners replace fans themselves—it’s mechanically simple and the pipe connections are straightforward PVC. The electrical connection should be handled by a licensed electrician if you’re not comfortable with wiring.

When to Test After Fan Installation or Replacement

After a new mitigation system is installed or a fan is replaced, test within 24 hours. Post-mitigation radon test levels confirm whether the system is working effectively. Most certified mitigators include this test.

Retest every two years under normal circumstances. After any significant changes to the home—new basement finishing, major foundation work, HVAC changes—retest as well.

Frequently Asked Questions

How much does it cost to run a radon fan? Standard radon fans consume 20–90 watts of electricity. At average US electricity rates, this works out to $20–$100 per year to run continuously—a very modest operating cost given the health benefit.

Can I turn off my radon fan at night to save electricity? No. Radon mitigation systems work through continuous depressurization. Turning the fan off allows pressure to equalize and radon to accumulate. Systems should run continuously.

My radon fan makes a clicking noise—should I be worried? Minor clicking can be caused by moisture condensation in the pipe that’s being disturbed by airflow. Persistent or loud clicking suggests the fan bearings may be failing. Contact your installer for an assessment.

Is there a way to test if my fan is working without a manometer? You can hold a piece of tissue near the suction-side of the pipe penetration in the floor—it should be pulled toward the pipe if suction is present. However, a manometer is a much more reliable indicator.

Does my radon fan need to be inspected by a professional? Not on a fixed schedule, but periodic check-ins are good practice. If the fan is more than 7 years old, a professional can assess whether it’s still performing at rated capacity.

For cost information, see our radon mitigation cost guide.

Find Local Radon Mitigation Specialists

For fan replacement, system check-ups, or new installations, RadonLocal connects you with certified radon contractors near you who can assess your specific system and recommend the best path forward.