Radon Level Over 20 pCi/L: Emergency Steps

A radon test above 20 pCi/L is among the highest readings in residential settings. This is five times the EPA action level or more. You need to take immediate steps to reduce exposure while arranging professional mitigation as fast as possible.

Immediate Safety Measures — Do These Today

While you arrange professional mitigation, take these steps right now to reduce radon concentration in your home:

• Open windows on the lowest level. Cross-ventilation dilutes indoor radon. Open windows on opposite sides of the basement or lowest floor. Yes, even in winter — short-term energy cost is trivial compared to the exposure reduction.
• Run a fan near a basement window. Pointing outward, a box fan creates active air exchange that can meaningfully lower concentrations temporarily.
• Limit time in the basement and lower levels. If your family uses the basement as a living space, playroom, or bedroom, relocate those activities upstairs until the system is installed. Radon concentrations are highest at the lowest point of the home.
• Seal open sump pits. If your sump pit lacks an airtight cover, use plastic sheeting and tape as a temporary seal. Open sumps are one of the largest single entry points for soil gas.
• Avoid running exhaust fans in upper levels. Bathroom and kitchen exhaust fans can increase the stack effect, pulling more soil gas into the house from below. Minimize their use until mitigation is complete.

These are temporary measures. They will not solve the problem. But they can reduce exposure meaningfully during the days or weeks before your mitigation system is operational.

Skip the Confirmation Test

At 20+ pCi/L, there is no practical scenario where a confirmation test changes the outcome. Even if your true annual average is 40% lower than your short-term test showed, you're still at 12 pCi/L — three times the EPA action level. The confirmation step adds delay without adding useful information.

The EPA and most radon professionals agree: at very high levels, proceed directly to mitigation. Contact contractors immediately.

Getting a Contractor Fast

Call multiple certified contractors and explain that your levels are above 20 pCi/L. Most reputable companies will prioritize high-level cases. In many markets, you can get an installation scheduled within one to two weeks.

When you're choosing under time pressure, focus on three things:

• Current certification. NRPP or NRSB credentials verify professional competency.
• Availability. In this situation, a certified contractor who can install next week is more valuable than one with a six-week waitlist.
• Post-install testing included. Verify they'll test after installation to confirm the system is working.

Our guide on choosing a radon mitigation contractor covers additional vetting criteria, but at this level, speed and certification are your top priorities.

Use our contractor directory to find certified professionals near you today.

What Mitigation Can Achieve at Very High Levels

Here's the reassuring part. Active soil depressurization works at very high levels. The same system that brings a home from 4 to below 2 pCi/L can bring a home from 30 or even 50 pCi/L down to safe ranges. The fan may need to be more powerful, or the system may require multiple suction points, but the technology is proven.

Typical post-mitigation results for homes that started above 20 pCi/L:

• Starting at 20-30 pCi/L: Post-mitigation levels commonly reach 1.0 to 3.0 pCi/L
• Starting at 30-50 pCi/L: Post-mitigation levels commonly reach 1.5 to 4.0 pCi/L
• Starting above 50 pCi/L: Systems may require additional suction points or higher-capacity fans, but results below 4.0 pCi/L are still achievable in most homes

Honestly, the percentage reduction at very high levels is often among the most dramatic. A home dropping from 40 to 2 pCi/L has achieved a 95% reduction — and that's not unusual for a well-designed system.

The Health Context

According to the EPA, a non-smoker living at 20 pCi/L faces roughly a 36 in 1,000 lifetime lung cancer risk from radon — comparable to many occupational hazard thresholds. For smokers, the combined risk at this level is severe. The EPA is clear that radon is the number one cause of lung cancer among non-smokers, and concentrations above 20 pCi/L represent the high end of residential exposure.

For the full picture on radon and health, see our radon health risks guide.

This part matters: the risk is cumulative and based on duration. You've been living with this level for some time already. Acting now — this week — limits your total future exposure. Every week you shave off the timeline between discovery and mitigation is meaningful.

After Installation

Post-mitigation testing is critical at high starting levels. Run a short-term test within 48 hours of system activation. If levels are below 4.0 pCi/L, the system is performing. Below 2.0 is ideal.

If levels remain above 4.0 after installation, contact your contractor for system optimization. This might mean adding another suction point, upgrading the fan, or improving foundation sealing. At very high starting levels, system tuning is sometimes needed — and a good contractor will have planned for this possibility.

Follow up with a long-term test through the next winter heating season, and retest every two years after that per EPA recommendations.

Take Action Now

Radon above 20 pCi/L is urgent but solvable. Open your windows today, limit basement time, and start calling certified contractors. The mitigation technology exists, it works at these levels, and most installs can happen within one to two weeks of scheduling. Your household's long-term health depends on acting quickly — and you have everything you need to start right now.