January is nationally recognized as Radon Awareness Month, and for homeowners in New Jersey and Pennsylvania, it is also the single best time of year to test for radon. Radon testing in winter provides the most accurate, conservative, and meaningful results because it captures how a home actually performs when it is closed up, heated, and occupied the way it is for much of the year.
Radon is a naturally occurring radioactive gas that comes from the breakdown of uranium in soil and rock. It has no smell, no taste, and no color, which means it can accumulate inside a home completely undetected. According to the U.S. Environmental Protection Agency (EPA), radon is the second leading cause of lung cancer overall and the leading cause among non-smokers, contributing to approximately 21,000 lung cancer deaths each year in the United States.
Because radon is invisible and unpredictable, testing is the only way to know if your home has a radon problem. Winter testing, in particular, gives homeowners, buyers, sellers, and landlords the most reliable picture of potential long-term exposure.
What Exactly Is Radon?
Radon is a radioactive gas produced naturally in the ground. As uranium decays in soil, rock, and groundwater, radon gas is released and migrates upward toward the surface. Outdoors, radon is diluted quickly and generally poses little risk. Indoors, however, radon can become trapped and concentrated to dangerous levels.
Once radon enters a building, it can accumulate in lower levels and circulate throughout the structure. Because radon gas is heavier than air, it often enters from below — but once inside, it mixes freely and can be present throughout the home.
Radon exposure is especially concerning because:
- It causes damage over long-term exposure
- Symptoms are typically not immediate
- Exposure often occurs without awareness
- Risk increases with duration and concentration
The EPA has established an action level of 4.0 picocuries per liter (pCi/L). However, the EPA also emphasizes that there is no safe level of radon, and mitigation may be appropriate even below 4.0 pCi/L depending on occupancy and risk tolerance learn more at: https://www.epa.gov/radon
How Radon Enters a Home
Radon enters homes through common and often unavoidable pathways. Even homes without visible foundation defects can experience elevated radon levels.
Typical entry points include:
- Cracks in concrete slabs
- Foundation wall cracks
- Floor-to-wall joints
- Sump pits and sump pump lids
- Crawlspace soil and block walls
- Plumbing, gas, and electrical penetrations
- Construction joints and control joints
Importantly, radon entry is driven by pressure differences, not just the presence of cracks. Homes act like vacuums, pulling soil gases upward whenever indoor air pressure is lower than soil pressure — a condition that is especially pronounced in winter.
Why Radon Testing in Winter Is More Accurate
Radon testing in winter is recommended by the EPA and most radon professionals because winter conditions naturally create worst-case radon entry scenarios.
Closed-House Conditions
During winter months, homes are typically sealed to conserve heat:
- Windows remain closed
- Exterior doors are used less frequently
- Fresh air exchange is reduced
- Mechanical systems recirculate indoor air
These closed-house conditions allow radon levels to stabilize and accumulate, providing a more representative assessment of exposure risk.
Stack Effect Is Strongest in Winter
The stack effect plays a major role in radon entry. Warm air inside the home rises and escapes through the upper portions of the structure. This creates negative pressure at lower levels, actively drawing soil gases — including radon — into the building.
The greater the temperature difference between indoors and outdoors, the stronger the stack effect. Winter months create the largest pressure differentials, making radon testing in winter particularly effective.
Reduced Ventilation Masking
In warmer seasons, open windows, fans, and natural ventilation can artificially lower radon readings. While this may appear reassuring, it often masks a real radon problem that returns once the home is closed up again.
Winter testing eliminates this false sense of security.
Radon Is Not Just a Basement Issue
One of the most common misconceptions about radon is that it only affects homes with basements. In reality, any home with ground contact can have elevated radon levels.
This includes:
- Slab-on-grade homes
- Crawlspace homes
- Split-level homes
- Townhomes and duplexes
- Homes built into slopes or hillsides
Radon problems are routinely identified in homes without basements due to:
- Slab cracks and shrinkage
- Plumbing and HVAC penetrations
- Expansion joints
- Perimeter foundation seams
We frequently test slab homes where homeowners assumed radon was “not a concern” — only to find elevated levels. The foundation type does not eliminate risk; soil contact and pressure dynamics are what matter – learn more about our radon testing https://dynamicinspections.net/radon-testing/
When Should You Test for Radon?
Radon testing is recommended in many situations, including:
- Purchasing a home
- Selling a home
- Homes that have never been tested
- Homes tested more than two years ago
- After renovations or foundation repairs
- After HVAC system changes
- After installing or modifying a radon mitigation system
The EPA recommends retesting every two years, even if previous results were below the action level. Retesting is also recommended after significant structural or mechanical change learn more about the CDC’s guidance on radon at: https://www.cdc.gov/radon
Professional Radon Testing vs DIY Test Kits
DIY radon test kits are widely available, but they have limitations that homeowners should understand.
Common limitations include:
- No verification of closed-house conditions
- No tracking of environmental conditions
- No tamper detection
- Results that may not be accepted for real estate transactions
Professional radon testing uses EPA-approved continuous radon monitors (CRMs) that:
- Measure radon levels hourly
- Track temperature, humidity, and pressure
- Detect movement or interference
- Provide detailed graphs and trend data
Professional testing provides results that are defensible, repeatable, and meaningful, especially in real estate and compliance scenarios.
What Happens During a Professional Radon Test?
A professional radon test typically involves:
- Placement of the monitor in the lowest livable level of the home
- Establishment of closed-house conditions
- A minimum 48-hour test period
- Data retrieval and analysis
- Delivery of a detailed report
Reports typically include:
- Average radon concentration
- Hourly readings
- Environmental data
- Clear interpretation of results
- Recommendations for next steps
Understanding Your Radon Results
Radon results are measured in picocuries per liter (pCi/L).
General guidance:
- Below 2.0 pCi/L: Low risk, retesting recommended periodically
- 2.0–4.0 pCi/L: Consider mitigation depending on occupancy
- 4.0 pCi/L and above: Mitigation recommended
Radon levels can fluctuate daily and seasonally, which is why winter testing provides the most conservative assessment.
What If Radon Levels Are Elevated?
If radon levels exceed recommended thresholds, mitigation is usually straightforward and highly effective.
Radon Mitigation Systems
Most homes can be mitigated using sub-slab depressurization, which:
- Removes radon from beneath the foundation
- Vents it safely above the roofline
- Reduces radon levels by up to 90% or more
Mitigation systems should:
- Be installed by a licensed radon mitigation contractor
- Include a manometer or monitoring device
- Be tested after installation
- Be periodically re-tested
Radon Testing and Real Estate Transactions
Radon testing is a common part of real estate transactions in New Jersey and Pennsylvania. Winter testing benefits both buyers and sellers by:
- Reducing disputes
- Avoiding seasonal retesting
- Providing conservative, defensible results
- Allowing informed negotiations
For sellers, proactive radon testing can prevent last-minute delays and renegotiations.
Why Choose Dynamic Inspections LLC?
Dynamic Inspections LLC provides professional radon testing throughout New Jersey and Pennsylvania, with a focus on education and accuracy.
- Licensed radon measurement technician
- EPA-approved testing protocols
- Professional-grade monitoring equipment
- Clear, unbiased reporting
- Focus on informing, not alarming
Final Thoughts: Test in Winter, Breathe Easier All Year
Radon testing in winter provides the most accurate snapshot of your home’s radon risk. Whether your home has a basement, crawlspace, or slab foundation, radon testing is essential to understanding long-term exposure.
January is the ideal time to test — and the peace of mind lasts all year.
If you’re considering radon testing in New Jersey or Pennsylvania, Dynamic Inspections LLC is here to help.