Most NJ Homeowners Don’t Know What a Radon Test Actually Involves — and That Gap Leads to Invalid Results, Missed Problems, and Negotiating Leverage Left on the Table.

Radon testing is one of the most important and most frequently mismanaged steps in New Jersey home ownership and real estate. Most people know they need a test. Far fewer understand what a valid test requires, what type of test is appropriate for their situation, or how to read the results in a way that leads to a sound decision. Jersey Radon’s certified radon mitigation team has performed thousands of tests across New Jersey, and the situations that lead to bad outcomes — invalid results, missed elevations, failed real estate negotiations — almost always trace back to a misunderstanding of the testing process itself. Here is what a professional radon test in your NJ home actually involves, from the moment you schedule to the moment you have a number you can act on.

Who Is Allowed to Perform a Radon Test in New Jersey?

New Jersey is one of the strictest states in the country regarding who may legally perform radon testing. According to the NJDEP Radon Testing and Mitigation Basics guide, it is against the law to perform radon testing or mitigation in New Jersey without state certification. Every technician who places or retrieves a radon test device in a residential property must hold a valid NJDEP radon measurement certification. This applies equally to independent inspectors, home inspection companies, and real estate professionals — none of them may place or retrieve test devices unless they are personally DEP-certified. For real estate transactions specifically, neither the homeowner, the buyer, the seller, nor the real estate agent may perform any part of the test — including starting it, stopping it, or mailing it to the laboratory. Only the DEP-certified technician may handle the test device from placement to laboratory submission.

You can verify a tester’s certification by calling the NJDEP Radon Information Line at (800) 648-0394 or by checking the NJDEP’s online directory of certified radon measurement companies. Hiring an uncertified contractor for radon testing in New Jersey — regardless of how it is advertised — produces results that may not be legally valid for a real estate transaction and that cannot be relied upon for mitigation decisions. Jersey Radon holds full NJDEP certification for both radon measurement and radon mitigation throughout New Jersey.

Can a Homeowner Test Their Own Home for Radon in NJ?

Yes — for non-real-estate purposes, a homeowner may purchase a DIY radon test kit and test their own home without hiring a certified professional. Test kits are available at hardware stores and through certified laboratories by mail. A DIY test is a reasonable and cost-effective option for a homeowner who wants to check their own home’s radon level outside of a transaction context. However, a DIY test result cannot be used in a real estate transaction — the buyer or seller cannot present a homeowner-administered test as a valid transaction test, and a buyer who uses a DIY result to make a mitigation decision is working with data that may not meet the DEP’s accuracy standards. For any home purchase or sale, a DEP-certified professional test is required.

What Are the Different Types of Radon Tests and When Is Each Used?

New Jersey recognizes two categories of radon test: short-term and long-term. Understanding the difference — and knowing which one applies to your situation — is essential for getting results that are accurate and actionable.

Short-term tests are conducted over 2 to 7 days using charcoal canisters, electret ion chamber devices, or continuous electronic radon monitors. The NJDEP considers all three device types equally reliable when used by certified technicians. Short-term tests are the standard for real estate transactions in NJ — the 2-to-7-day window fits within typical inspection periods, and a single short-term test at or above 4 pCi/L is considered by the NJDEP to predict actual levels in 80% of cases. If two short-term tests are conducted simultaneously and averaged, the result is considered slightly more accurate than a single test. Short-term tests are also appropriate for initial screening when a homeowner wants a quick indication of whether radon is a concern in their home.

Long-term tests are conducted over 90 days to 12 months using alpha track detectors or electret devices. They provide the best estimate of the actual average radon exposure over time, since radon levels fluctuate daily and seasonally. A long-term test that includes winter months — when NJ homes are typically more tightly sealed and radon concentrations are higher — is considered the most representative measure of annual exposure. The NJDEP recommends long-term testing for homeowners who want an accurate picture of their ongoing exposure rather than a transactional snapshot. If a short-term test produces a borderline result (between 2 and 4 pCi/L), a follow-up long-term test is the appropriate way to determine whether the level justifies mitigation.

What Are Closed-House Conditions and Why Do They Matter?

Closed-house conditions are the single most important procedural requirement for a valid short-term radon test — and the requirement most frequently violated, either intentionally or accidentally. Closed-house conditions mean that all windows and exterior doors on all floors of the home must remain closed except for normal entry and exit during the entire test period. For tests lasting less than four days, closed-house conditions must be established at least 12 hours before the test device is placed. For tests of four to seven days, the 12-hour pre-test period still applies. Heating and central air conditioning systems should operate normally. Window-mounted air conditioners must be set to recirculation or vent-closed mode — not to draw outside air. Attic fans, whole-house fans, and wood-burning fireplaces should not be operated during the test unless they are the primary heat source.

The reason for these requirements is that outdoor air, which typically contains radon at the outdoor background level of roughly 0.4 pCi/L, dramatically dilutes indoor radon concentrations when ventilation occurs. A home that tests at 6 pCi/L under proper closed-house conditions might test at 3 pCi/L if windows were open throughout the test — a reading that would falsely indicate the home is below the action level. For real estate transactions, tampering with a radon test — including opening windows or doors during the test period — is illegal in New Jersey and can result in penalties. Any technician conducting a professional test will confirm closed-house conditions at both the start and end of the test and document weather and temperature conditions on the data sheet.

What Happens If Closed-House Conditions Are Violated?

A test conducted without proper closed-house conditions produces an invalid result — one that cannot be relied upon for mitigation decisions or used in a real estate transaction. If a certified technician discovers that conditions were violated when retrieving the test device (open windows, evidence of heavy ventilation), the test is typically voided and must be repeated. In a real estate context, this can complicate timelines significantly. Buyers who discover that a seller-arranged radon test was conducted under improper conditions — even unintentionally — have grounds to require a new test under proper conditions before closing. This is why independent testing arranged by the buyer, through a DEP-certified company of the buyer’s choosing, is the most reliable approach for transaction testing.

What Does a Continuous Electronic Radon Monitor Do Differently?

Continuous electronic radon monitors (CRMs) are an alternative to passive charcoal and electret devices that provide hour-by-hour radon concentration readings throughout the test period rather than a single integrated average. CRMs are used exclusively by certified professionals — they cannot be purchased by homeowners for DIY testing. The detailed hourly record they produce serves two purposes: it provides the averaged result used to determine whether action is warranted, and it documents whether test conditions were maintained throughout the measurement period. Unusual patterns in the hourly data — large concentration spikes or drops that correspond to specific times of day — can indicate ventilation disruptions, drafts affecting the device, or tampering. For real estate transactions where there is any question about test integrity, a CRM record provides an auditable history that a passive device cannot. Jersey Radon uses continuous monitors for all transaction testing, and the full hourly data record is available to all parties.

Where Is the Test Device Placed and Does Location Matter?

Placement location affects the test result meaningfully, and the NJDEP provides specific guidance on where devices must and must not be placed. The test device must be placed in the lowest livable level of the home — the lowest level that is used or could be used as living space without major renovation. For a home with an unfinished basement that could be converted to living space, the test goes in the basement. For a slab-on-grade home with no basement, the test goes on the first floor. The device must be placed between 20 inches and 1.5 meters above the floor, away from drafts, exterior doors, windows, HVAC supply and return vents, and areas of high humidity. It must not be placed in a kitchen, bathroom, laundry room, closet, or crawl space.

The room placement matters too. A finished basement room that is regularly used as a bedroom or family room is a more representative location than a mechanical room or storage area that the family rarely occupies. The test is measuring the radon exposure that people actually experience — and if a family spends significant time in a basement home office, that space is where the test should be placed. For homes where different areas are used differently, testing more than one location provides a more complete picture. Our 20 radon facts page covers why lower floors always have higher concentrations and what that means for placement decisions.

• Lowest livable level — basement, first floor if no basement, or ground-level floor of slab-on-grade
• Between 20 inches and 1.5 meters above the floor — not on the floor or at ceiling height
• Away from windows, exterior doors, HVAC vents, and high-humidity areas
• Not in kitchens, bathrooms, laundry rooms, closets, or crawl spaces
• In a room that is regularly occupied — not a storage room or mechanical area
• Away from direct sunlight, which can affect some device types

How Long Does a Professional Radon Test Take and What Are the Steps?

For a standard short-term real estate test, the process unfolds over approximately two to seven days from device placement to result. The certified technician arrives, confirms that closed-house conditions have been maintained for the required pre-test period, completes the data sheet with property and environmental information, and places the test device in the appropriate location. The property owner signs to acknowledge the test conditions and waive or maintain confidentiality of the results per New Jersey regulations — for real estate transactions, results are automatically submitted to the NJDEP by the laboratory. During the test period, the home must maintain closed-house conditions continuously. At the end of the test period, the certified technician returns to retrieve the device, documents the final conditions, and submits the device to the laboratory. Results are typically available within one to two weeks of laboratory receipt, though some continuous electronic monitors can provide near-real-time results.

How Do You Read and Interpret a Radon Test Result?

Radon test results are reported in picocuries per liter (pCi/L). The EPA and NJDEP action level is 4 pCi/L — the concentration at which both agencies recommend taking action to reduce indoor radon. The national average indoor radon level is approximately 1.3 pCi/L. A result between 2 and 4 pCi/L falls in a gray zone where mitigation is worth considering, particularly if the family spends significant time on lower floors, if long-term testing produces a similar result, or if the home is in one of NJ’s Tier 1 radon counties. A result at or above 4 pCi/L warrants mitigation. A result above 10 pCi/L warrants prompt mitigation.

For real estate transactions, a result at or above 4 pCi/L gives the buyer grounds to request mitigation as a condition of sale, negotiate a credit, or in some cases exit the contract depending on what the radon contingency clause specifies. Our page on water quality and radon due diligence for NJ home buyers covers how to structure radon contingencies in a purchase contract. For homeowners with private wells in northern NJ counties, elevated air radon should also prompt a water radon test, since the same uranium-bearing bedrock geology drives both. Our radon in well water page explains the water-to-air transfer relationship.

What Happens After You Get Your Radon Test Results?

A result below 4 pCi/L requires no immediate action beyond scheduling retesting every two years and before any significant structural renovation. A result at or above 4 pCi/L requires engagement with a NJDEP-certified radon mitigation contractor — in New Jersey, both testing and mitigation require separate certifications, and a company that only holds a testing certification cannot perform the mitigation work. Jersey Radon holds both certifications, which means we can take a home from initial test through mitigation design, installation, and post-mitigation verification without requiring the homeowner to coordinate multiple contractors. Our radon removal service page covers the mitigation process, typical system designs for different NJ foundation types, and what to expect from installation to final verification testing.

Getting an Accurate Radon Test for Your NJ Home

A radon test is only as useful as the process behind it. Valid closed-house conditions, correct device placement, DEP-certified technicians, and results interpreted in the context of the home’s specific situation — these are the elements that turn a radon test from a checkbox into actionable information. Jersey Radon’s licensed radon measurement and mitigation team serves residential homeowners and home buyers throughout New Jersey, and we bring the same rigor to initial testing that we bring to every mitigation installation we perform.

If you need a radon test for your NJ home — for a real estate transaction, for an initial baseline, or to retest after renovation — contact us for a free estimate or call us directly at (732) 357-1988. We serve all of New Jersey and are available any time.