Radon in Pennsylvania Homes: What Buyers Must Know
Why Radon Is a Serious Issue for Pennsylvania Homebuyers
Pennsylvania has the highest radon levels of any state in the country. Roughly 40% of homes statewide test above the EPA’s recommended action level of 4.0 picocuries per liter (pCi/L). In some counties, particularly in the southeastern and south-central regions, that figure exceeds 50%.
Radon is a naturally occurring radioactive gas produced by the decay of uranium in rock and soil. It seeps into homes through cracks in foundations, gaps around pipes, and porous concrete. You can’t see it, smell it, or taste it. The only way to know if a home has elevated radon is to test.
The EPA identifies radon as the second leading cause of lung cancer after smoking, responsible for an estimated 21,000 deaths per year in the United States. For homebuyers in Pennsylvania, radon testing should be treated as a standard part of every real estate transaction — not an optional add-on.
How Radon Enters Your Home
Radon forms in the soil beneath and around your home. Because the air pressure inside your house is typically lower than the pressure in the soil underneath, your home acts like a vacuum, drawing radon gas up through any available pathway:
- Cracks in poured concrete foundations — even hairline cracks provide entry points
- Gaps between the foundation floor and walls (the cove joint)
- Openings around sump pumps and drains
- Gaps around pipes, conduits, and wires entering the foundation
- Porous concrete blocks in block foundations
- Exposed soil in crawl spaces
- Well water — radon dissolved in groundwater can release into household air when water is used
Radon levels vary significantly from home to home, even between adjacent properties on the same street. The underlying geology, the home’s construction type, foundation condition, ventilation, and soil permeability all affect how much radon enters and accumulates.
Pennsylvania’s Radon Risk by County
The Pennsylvania Department of Environmental Protection (DEP) classifies counties into three tiers based on radon potential:
Tier 1 (Highest Risk): Counties where the predicted average indoor radon screening level is greater than 4.0 pCi/L. Testing is strongly recommended for every home.
Tier 2 (Moderate Risk): Counties where the predicted average is between 2.0 and 4.0 pCi/L. Testing is still recommended.
Tier 3 (Lower Risk): Counties where the predicted average is below 2.0 pCi/L. Testing is still recommended — individual homes can have high radon regardless of the county average.
| Tier | Counties |
|---|---|
| Tier 1 (Highest) | Adams, Berks, Bucks, Carbon, Centre, Chester, Clinton, Columbia, Cumberland, Dauphin, Delaware, Franklin, Huntingdon, Juniata, Lackawanna, Lancaster, Lebanon, Lehigh, Luzerne, Lycoming, Mifflin, Monroe, Montgomery, Montour, Northampton, Northumberland, Perry, Pike, Schuylkill, Snyder, Sullivan, Susquehanna, Union, Wayne, Wyoming, York |
| Tier 2 (Moderate) | Allegheny, Armstrong, Bedford, Blair, Bradford, Cambria, Cameron, Clarion, Clearfield, Elk, Erie, Fayette, Forest, Fulton, Greene, Indiana, Jefferson, McKean, Mercer, Potter, Somerset, Tioga, Venango, Warren, Washington, Westmoreland |
| Tier 3 (Lower) | Beaver, Butler, Crawford, Lawrence, Philadelphia |
Note: Even in Tier 3 counties, individual homes can test well above 4.0 pCi/L. The tier designation reflects a county average, not a guarantee for any specific property.
The southeastern corridor — including the Philadelphia suburbs in Montgomery, Chester, Bucks, and Delaware counties — is one of the highest radon areas in the nation. The underlying Reading Prong geological formation produces exceptionally high radon levels. If you’re buying in this region, radon testing is not optional.
For Philadelphia-area buyers, our Philadelphia relocation guide covers housing costs and neighborhood details.
How Radon Testing Works
Two types of radon tests are commonly used in real estate transactions:
Short-term tests (2-7 days): These are the standard for real estate transactions. A certified tester places continuous radon monitors (CRMs) or charcoal canisters in the lowest livable level of the home for a minimum of 48 hours. During the test period, the home should remain under “closed-building conditions” — windows and doors closed, HVAC operating normally.
Long-term tests (90+ days): These provide a more accurate picture of year-round radon exposure since levels fluctuate seasonally. Long-term tests are better for homeowners who want to understand their actual exposure but aren’t practical for real estate transactions where timing is tight.
For a home purchase, the typical process:
- Your home inspector places CRM devices during the home inspection
- The monitors run for 48 hours minimum under closed-building conditions
- The inspector retrieves the monitors and downloads the data
- Results are usually available within 24 hours of pickup
- If results are above 4.0 pCi/L, you can negotiate mitigation with the seller
What the Test Results Mean
The EPA has established guidelines for interpreting radon test results:
| Test Result (pCi/L) | EPA Recommendation | Action |
|---|---|---|
| Below 2.0 | Low risk | No action needed, but consider retesting every 2-5 years |
| 2.0 – 3.9 | Moderate risk | Consider mitigation, especially if level is closer to 4.0 |
| 4.0 – 7.9 | Above action level | Mitigation recommended within a few months |
| 8.0 – 19.9 | High | Mitigation recommended within weeks |
| 20.0+ | Very high | Take immediate steps to reduce levels |
The EPA’s action level of 4.0 pCi/L is not a “safe” level — it’s the level at which the EPA recommends taking action. The World Health Organization sets its reference level at 2.7 pCi/L. Any radon exposure carries some risk; the goal of mitigation is to reduce levels as low as reasonably achievable.
Testing Costs
Radon testing costs in Pennsylvania typically range from $125 to $300 depending on the method and provider:
- Home inspector add-on (CRM): $125-$200 when bundled with a standard home inspection. This is the most common approach for real estate transactions.
- Standalone professional test (CRM): $150-$250 from a DEP-certified radon tester.
- DIY test kit (charcoal canister): $15-$40 at hardware stores or online. Suitable for screening but not typically accepted in real estate transactions because they lack chain-of-custody controls.
- Long-term alpha track test: $25-$50 for the kit. Takes 90+ days. Good for homeowners evaluating ongoing exposure.
Always use a Pennsylvania DEP-certified radon tester for real estate transactions. You can verify certification through the DEP’s online radon certification database.
Radon Mitigation: How It Works and What It Costs
If testing reveals radon above 4.0 pCi/L, a mitigation system can reduce levels by 90% or more. The most common system is sub-slab depressurization (SSD):
How SSD works:
- A hole is drilled through the basement floor slab to the gravel or soil beneath
- A PVC pipe is inserted into the hole
- The pipe runs from the sub-slab area, through the house (or along the exterior), up through the roof
- A radon fan mounted on the pipe creates suction beneath the slab
- The fan continuously pulls radon from under the foundation and vents it above the roofline, where it disperses harmlessly
Mitigation costs:
| System Type | Cost Range | Best For |
|---|---|---|
| Sub-slab depressurization (standard) | $800-$1,500 | Homes with slab or basement floor |
| Sub-slab depressurization (complex) | $1,500-$2,500 | Large homes, multiple suction points, stone foundations |
| Sub-membrane depressurization | $1,200-$2,500 | Homes with dirt-floor crawl spaces |
| Drain tile suction | $800-$1,500 | Homes with existing perimeter drain tile |
| Heat recovery ventilator (HRV) | $1,500-$3,000 | When SSD isn’t feasible or as supplemental |
Most residential mitigations in Pennsylvania fall in the $1,000-$1,800 range. The system operates continuously, using about $50-$100 per year in electricity for the fan. Annual maintenance is minimal — mainly checking the manometer (pressure gauge) on the pipe to confirm the fan is operating and replacing the fan every 8-12 years ($200-$400).
After installation, the mitigator should conduct a post-mitigation test to confirm radon levels dropped below 4.0 pCi/L. Most systems reduce levels to below 2.0.
How Radon Affects Real Estate Transactions
Radon regularly comes up during home purchase negotiations in Pennsylvania. Here’s how it typically plays out:
Scenario 1: Radon below 4.0 pCi/L. No action required. The transaction proceeds normally. The test results should be kept for future reference.
Scenario 2: Radon above 4.0 pCi/L, no existing mitigation system. The buyer typically requests the seller install a mitigation system before closing, or the buyer requests a credit toward installation costs. Most sellers agree because radon mitigation is relatively affordable and refusing can cause the deal to fall apart.
Scenario 3: Radon above 4.0 pCi/L, existing mitigation system present. The system may not be operating properly, or the fan may have failed. Request a post-mitigation test to verify the system is actually reducing radon to acceptable levels. If the system needs repair or replacement, negotiate accordingly.
Scenario 4: Seller already tested and levels were low. The seller’s test results may be included in the disclosure. However, radon levels fluctuate over time. If the seller’s test was done more than 2 years ago, or during a different season, a new test during your inspection period is reasonable.
In very competitive markets, some buyers waive radon contingencies to strengthen their offers. This is risky in Pennsylvania given the prevalence of elevated radon. Even if you waive the contingency, you can (and should) still test after closing and mitigate if needed.
To estimate how radon mitigation costs factor into your total closing expenses, use our closing cost calculator.
Radon in Well Water
Radon dissolved in groundwater is a concern for Pennsylvania homeowners with private wells. When water containing radon is used — for showers, dishwashing, laundry — the gas releases into indoor air. The EPA estimates that water use contributes to about 1-2% of total indoor radon, but in some cases it can be a significant source.
There’s no federal standard for radon in water, but the EPA has proposed a maximum contaminant level (MCL) of 300 pCi/L for community water systems and an alternative MCL of 4,000 pCi/L for systems with multimedia mitigation programs.
If you have a private well and your indoor air radon levels are elevated even after installing a sub-slab system, have your water tested for radon separately. Water radon testing costs $30-$100 through a certified lab.
Treatment options for radon in water include:
- Granular activated carbon (GAC) filter: Effective for levels up to about 10,000 pCi/L. Cost: $1,000-$2,500 installed. Requires periodic filter replacement.
- Aeration system: Removes radon by bubbling air through the water, then venting the radon outdoors. More effective than GAC for very high levels. Cost: $3,000-$5,000 installed.
Radon in New Construction
New homes are not immune to radon. In fact, modern tightly sealed construction can trap radon more effectively than older, leakier homes. Pennsylvania’s building codes include provisions for radon-resistant new construction (RRNC) in Tier 1 and Tier 2 counties.
RRNC features include:
- A gas-permeable layer (gravel) beneath the slab
- Polyethylene sheeting over the gravel as a soil gas retarder
- Sealed foundation penetrations
- A 3 or 4-inch PVC vent pipe from the sub-slab area through the roof
- An electrical junction box near the pipe for future fan installation if needed
Even with RRNC features, test new homes for radon after construction. If levels are above 4.0, activating the passive system (by adding a fan to the existing vent pipe) typically costs $300-$600 — much less than retrofitting a mitigation system.
Long-Term Radon Management
If you install a mitigation system or buy a home with one already in place, ongoing management is minimal but important:
- Check the manometer monthly. The u-tube gauge on the radon pipe shows system pressure. If both sides are level, the fan isn’t running. If the liquid shows a difference between the two sides, the system is operating.
- Listen for the fan. A properly running radon fan makes a quiet humming sound. If the fan stops or starts making unusual noises, it needs service.
- Retest every 2 years. Use a long-term test kit to verify the system continues to maintain low radon levels. Environmental changes, foundation settling, and system wear can affect performance over time.
- Replace the fan when it fails. Radon fans typically last 8-12 years. Replacement costs $200-$400 including labor. Some mitigators offer fan warranties.
- Maintain the system during home improvements. If you finish a basement, add an addition, or make changes to the foundation, have your mitigation system evaluated to ensure it still provides adequate coverage.
Choosing a Radon Professional
Pennsylvania requires radon testers and mitigators to be certified by the Department of Environmental Protection. When hiring a radon professional:
- Verify their DEP certification online before hiring
- Ask for references and check reviews
- Get at least two quotes for mitigation work
- Confirm the mitigator will conduct a post-mitigation test
- Ask about their warranty — reputable mitigators guarantee their system will reduce radon below 4.0 pCi/L
- The tester and mitigator should not be the same person (to avoid conflict of interest), though some companies have separate certified personnel for each function
For help finding qualified home service professionals in your area, including radon testers and mitigators, visit our service directory.
Frequently Asked Questions
Should I avoid buying a home with high radon levels?
No. Radon is a solvable problem. A properly installed mitigation system reduces radon levels by 90% or more, typically bringing them well below the EPA action level. The cost of mitigation ($800-$2,500) is modest relative to the price of a home. Many homes in Pennsylvania have radon mitigation systems that operate quietly and effectively for years. The presence of elevated radon — or even an existing mitigation system — should not be a deal-breaker. A home that has been tested and mitigated is actually safer than a home that has never been tested.
Can radon levels change over time?
Yes. Radon levels fluctuate based on season (typically higher in winter when homes are sealed up), weather patterns, soil moisture, and changes to the home’s ventilation or foundation. A single short-term test provides a snapshot, not a permanent reading. Long-term testing (90+ days) gives a more accurate picture of average exposure. Even after mitigation, retest every 2 years to confirm levels remain low.
Does a radon mitigation system affect home resale value?
A properly installed and documented mitigation system can actually be a selling point. It shows that the home has been tested, the problem was addressed, and the system is working. Buyers in Pennsylvania are generally well-informed about radon and may prefer a home with a known-low radon level over one that has never been tested. Disclose the system’s presence, installation date, and most recent test results in your seller disclosure.
Is there a safe level of radon?
There is no known safe level of radon exposure. The EPA’s action level of 4.0 pCi/L is a recommended threshold for taking action, not a safety standard. The risk of lung cancer from radon increases with both the concentration and the duration of exposure. The goal should be to reduce levels as low as possible. Most mitigation systems bring indoor radon down to 1.0-2.0 pCi/L, which significantly reduces risk but doesn’t eliminate it entirely.
Does finishing a basement increase radon levels?
Finishing a basement can increase radon levels if the work seals cracks that previously allowed some radon to escape, or if the finished space becomes a more tightly sealed room. Conversely, if the finishing work includes sealing foundation cracks and gaps, it might reduce entry points. The effect is unpredictable. Always retest after finishing a basement. If you’re planning a basement renovation, this is a good time to install a mitigation system proactively — the cost is lower when done during construction rather than after.
Buying a home in Pennsylvania? Start with our affordability calculator to determine your budget, then use the property tax calculator to estimate your annual taxes. For a full overview of the purchase process, visit our homebuying guide.