Radon Level 10-20 pCi/L — High Radon Action Guide

A radon reading between 10 and 20 pCi/L is high. Not "maybe you should think about it" high — this is "schedule a contractor this week" high. But it's also not a reason to evacuate your home. Let's walk through exactly what this means and what to do.

Understanding the Risk

Not gonna sugarcoat this. At 10 to 20 pCi/L, the health risk is real and measurable. According to EPA estimates, a non-smoker living at 10 pCi/L faces approximately an 18 in 1,000 lifetime risk of lung cancer from radon. At 20 pCi/L, that roughly doubles to about 36 in 1,000. For smokers, the numbers are dramatically worse — the combined effect of radon and tobacco is multiplicative, not additive.

The EPA identifies radon as the leading cause of lung cancer among non-smokers in the United States, contributing to approximately 21,000 deaths annually. At concentrations between 10 and 20 pCi/L, your household is in a higher-risk bracket that justifies fast, decisive action.

For more on the health science, see our radon health risks guide.

Don't Panic — But Do Act Fast

Radon risk is about long-term cumulative exposure, measured in years and decades. A few weeks at this level while you arrange mitigation is not going to cause harm by itself. What matters is reducing the exposure as soon as reasonably possible.

Think about it this way: you've probably been living with this level for a while without knowing it. Now you know, and that knowledge gives you the power to fix it. The sooner you act, the more cumulative exposure you prevent going forward.

Immediate Steps You Can Take Today

• Increase ventilation. Open windows in the lowest level of your home when weather permits. This won't solve the problem, but it dilutes radon concentration temporarily.
• Limit time in the lowest level. If your basement is a primary living space, spend less time there until the system is installed.
• Seal obvious gaps. Visible cracks in the slab, open sump pits, and gaps around pipe penetrations are direct pathways. Sealing alone won't fix the problem, but it can help reduce entry slightly.

Confirmation Testing vs Going Straight to Mitigation

At 4 or 5 pCi/L, the EPA recommends confirmation testing before mitigation. At 10 to 20, the calculus changes. Many radon professionals and the EPA itself suggest that at levels this high, homeowners can proceed directly to mitigation without a second test.

Here's the reasoning. Even if your actual annual average is 30% lower than your test showed, you're still well above the action level. A test that reads 12 pCi/L is not going to average out to 3.5 over a year. The margin between your result and the action level is too wide for seasonal variation to close.

That said, if you want the data, you can run a second short-term test simultaneously with the contractor selection process. There's no reason the two steps can't overlap.

Choosing a Contractor at This Level

At 10 to 20 pCi/L, contractor selection matters — but not because the system design is exotic. Standard active soil depressurization works at these levels just as effectively as it does at lower concentrations. What matters is choosing someone who will design the system correctly from the start, so you don't end up with post-mitigation levels that are merely "less bad" instead of genuinely low.

Specifically, ask about:

• How many suction points they plan to install and why
• Whether they'll run diagnostic testing to confirm pressure field extension
• What post-mitigation result they expect to achieve
• Whether the quote includes a post-install radon test

Our guide on how to choose a radon mitigation contractor covers the full list of questions to ask before signing.

Find certified professionals near you through our contractor directory.

What to Expect From Mitigation

Standard systems reduce radon by 80% to 99% in most homes. A home starting at 15 pCi/L can typically expect post-mitigation levels between 0.5 and 3.0 pCi/L. Many end up below 2.0. That's a reduction from serious health risk to near-outdoor background levels.

Installation is still a one-day job for most homes. The system components are the same — suction point, PVC piping, fan, roofline vent. At higher starting levels, the contractor may size the fan slightly larger or add an additional suction point to ensure adequate pressure field coverage, but these are standard adjustments, not major redesigns.

Cost remains in the typical $800 to $2,500 range for most residential installations. Higher radon levels don't inherently cost more to fix — it's the home's foundation, layout, and soil conditions that drive pricing. Review the full breakdown in our cost guide.

After the System Is Installed

Run a post-mitigation test within 48 hours of system activation. If the result is below 2.0 pCi/L, the system is performing well. If it's between 2.0 and 4.0, discuss optimization with your contractor — additional sealing or a second suction point might be warranted.

Follow up with a long-term test through the next heating season. This confirms that performance holds during peak radon conditions. And continue retesting every two years as the EPA recommends.

One thing worth knowing: homes that start at high levels sometimes need minor system adjustments in the first year. This is normal and usually covered under the contractor's warranty. A good contractor will tell you upfront what their adjustment policy is.

Act This Week

At 10 to 20 pCi/L, the priority is clear. Start contacting certified contractors now. You can handle confirmation testing in parallel if you want the data, but don't let it delay the mitigation process. Every month of exposure at this level adds to your household's cumulative risk, and the fix is proven, fast, and affordable.