Radon levels by county in New York differ a lot in the State Health Department’s test-kit results: 3.7% of Queens basements tested at or above the EPA action level of 4 pCi/L, against 17.5% of Westchester basements. Yet EPA puts all eight of those counties in its lowest-radon zone. The county map and your house are different things. This guide shows the numbers, then explains what they can and cannot tell you.
The author is Inspecwise, a home inspector based in South Ozone Park, Queens, with a New York State license and InterNACHI certification. Radon is not part of a home inspection in New York: the State’s definition of a home inspection says it shall not include an inspection for radon or pests. It is a separate test, so this guide is about the data and about how to buy the right test, not about our inspection. Our older posts cover what a safe radon level is and radon test costs; this one is the data-led view by county, and it gives no prices.
Radon levels by county in New York: the state test data
The New York State Department of Health Radon Program provides short-term charcoal test kits through a contract laboratory and keeps every result. Its open data, cumulative from 1987 and updated in November 2025, count the kits placed in a basement and on a first floor. The table shows the share of homes tested at or above 4 pCi/L, which is the level at which EPA and the State both recommend fixing a home. The county file has no rows for four of the boroughs; their rows come from the same program’s town file. The “five boroughs together” row is the State’s combined New York County row.
| Area | Basements tested | Basements at or above 4 pCi/L | Mean (pCi/L) | Highest (pCi/L) | First floors tested | First floors at or above 4 pCi/L |
|---|---|---|---|---|---|---|
| Queens | 598 | 3.7% | 1.26 | 23.8 | 118 | 0.8% |
| Brooklyn (Kings) | 528 | 10.2% | 2.07 | 41.2 | 116 | 2.6% |
| Manhattan (New York) | 131 | 12.2% | 2.09 | 49.5 | 68 | 2.9% |
| The Bronx | 101 | 7.9% | 1.73 | 20.9 | 43 | 4.7% |
| Staten Island (Richmond) | 253 | 6.3% | 1.38 | 14.1 | 64 | 6.3% |
| Five boroughs together | 1,611 | 7.2% | 1.64 | 49.5 | 409 | 2.9% |
| Nassau County | 837 | 5.7% | 1.48 | 13.9 | 246 | 1.2% |
| Suffolk County | 580 | 7.6% | 1.84 | 42.6 | 232 | 2.2% |
| Westchester County | 2,875 | 17.5% | 2.84 | 95.4 | 799 | 5.3% |
Source: NYS Department of Health Radon Program, Radon Test Results by County and by Town, health.data.ny.gov, cumulative 1987 to the November 2025 update. Shares are the tests from 4 to 20 pCi/L plus the tests over 20, divided by homes tested (our arithmetic).
A few things stand out. Westchester’s basement share, 17.5%, is the highest and rests on the most tests (2,875). Queens is the lowest at 3.7%. Brooklyn (10.2%) and Manhattan (12.2%) sit above the Bronx (7.9%) and Staten Island (6.3%), but the Bronx and Manhattan figures rest on only 101 and 131 basements, so do not read small gaps as a ranking. Nassau (5.7%) and Suffolk (7.6%) fall in between. And the first-floor share is lower than the basement share everywhere except Staten Island, where the two are about the same on small numbers. The State’s Wadsworth Center says that basement radon concentrations average between 2 to 3 times higher than first-floor concentrations.
What a county figure does and does not tell you about one house
It describes kits, not every home
These results come from kits ordered through the State program. The State’s own note says the data may not be reflective of all radon tests in New York, because approximately 30,000 to 40,000 tests a year are not purchased through the program; they are done by home owners, inspectors, schools and others. It also warns that in some places only a few DOH-kit results exist, so care is needed. We read that as meaning the shares are not a random sample of homes. The numbers show what the kits found, not the share of all houses above 4.
A mean and a maximum are different things
The mean is pulled by a few high readings. Manhattan’s first-floor mean of 2.70 pCi/L is the highest first-floor mean in the table, yet only 2 of its 68 first-floor tests were at or above 4. The highest single first-floor reading in the table, 146.7 pCi/L, is also in Manhattan. By our arithmetic from the published mean, the other 67 tests average about 0.55 pCi/L, so one house moved the mean. The highest basement reading in Westchester, 95.4 pCi/L, tells you what is possible in a county with a low zone, not what is typical.
The EPA zone is a prediction, the kit is a measurement
EPA’s map of radon zones puts Zone 3 counties at a predicted average indoor screening level below 2 pCi/L, and its county file lists the Bronx, Kings, New York, Queens, Richmond, Nassau, Suffolk and Westchester as Zone 3. The State’s kit results show that 17.5% of Westchester basements tested at 4 or more. EPA’s own map says that all homes should be tested, regardless of zone designation, and the Wadsworth Center says that even where indoor radon is below average, it is prudent to measure.
Inside a county, the spread is wide
The same program’s town file shows how much a county number hides. This table takes the town or city labels with at least 50 basements tested and shows the lowest and the highest.
| County | Labels with 50+ basements tested | Lowest share at or above 4 pCi/L | Highest share at or above 4 pCi/L |
|---|---|---|---|
| Nassau | 3 of 5 | Hempstead 2.7% (401 basements) | Oyster Bay 8.7% (231 basements) |
| Suffolk | 5 of 11 | Babylon 1.7% (60 basements) | Smithtown 12.5% (64 basements) |
| Westchester | 20 of 24 | New Rochelle 8.8% (148 basements) | Lewisboro 33.7% (86 basements) |
The labels are the Health Department’s town, city or village names as entered, not ZIP codes or neighborhoods. Within Westchester the range is from 8.8% to 33.7%. A buyer in Lewisboro and a buyer in New Rochelle are in the same county and in very different positions. The open data files do not break New York City down below the borough, so for a city house the borough figure is as close as these State data come.
Days or months: how long a radon test runs
Radon moves with the weather and the season. EPA says a short-term test is less likely than a long-term test to tell you your year-round average radon level, because radon levels tend to vary from day to day and season to season. The table sets out the choice using EPA’s and the State’s wording.
| Feature | Short-term test | Long-term test |
|---|---|---|
| How long it stays in the home | Two days to 90 days, depending on the device (EPA) | More than 90 days (EPA) |
| What it tells you | A snapshot; less likely to match the year-round average | A reading more likely to match the year-round average |
| Closed-house conditions | Close windows and outside doors at least 12 hours before a 2 or 3 day test (EPA); the State asks for doors and windows to the outside closed 24 hours before and during the test | Follow the instructions that come with the kit (EPA) |
| Where it goes | The lowest lived-in level of the home (EPA) | The lowest lived-in level of the home (EPA) |
| Typical use | Screening, and quick answers in a sale | A better picture of the year-round level after a high short-term result |
EPA’s sequence is simple. Take a short-term test first. If the result is 4 pCi/L or higher, follow up with a long-term test for a better picture of the year-round average, or with a second short-term test if you need results quickly. For a home sale, EPA says two short-term tests done side by side, four inches apart, can be used to decide whether to fix the home. The State’s county figures above are short-term kit results, which is one more reason they are screening data, not a verdict on a house.
The State also names the moment to test: when buying a home and after major renovations, and before buying it advises that you hire a certified radon testing professional. EPA says levels below 4 pCi/L still pose a risk, so a result under the action level does not mean there is no risk.
What to do with a result: EPA’s steps and what fixing involves
For scale, EPA estimates the average indoor radon level at about 1.3 pCi/L and says about 0.4 pCi/L is normally found in outdoor air. The State’s basement means in the table run from 1.26 to 2.84. EPA’s guide sets out what to do with your own number.
| Your result | EPA’s next step |
|---|---|
| Under 4 pCi/L | No action level reached, but EPA says levels below 4 still pose a risk. Retest if you begin to use a lower level of the home |
| 4 pCi/L or higher on a first short-term test | Take a follow-up test: a long-term test for the year-round picture, or a second short-term test if you need results quickly |
| More than twice the action level (over 8 pCi/L) | Take a second short-term test immediately |
| After the follow-up | Fix the home if a long-term result is 4 or more; with two short-term tests, consider fixing if their average is 4 or higher |
| After a fix | Test again to be sure levels have dropped, and EPA suggests retesting every two years |
EPA says radon reduction systems work and that some can cut levels by up to 99 percent; most homes today can be reduced to 2 pCi/L or below. The main method is a vent pipe and fan that pulls radon from beneath the house and vents it outside. Lowering high levels takes a contractor trained to fix radon problems, which is why the credentials in the next section matter. EPA adds a warning for anyone planning a basement conversion: test the area before the renovation begins, and test again after the work, because major renovations can change the level of radon in a home.
Who is certified to test and fix radon in New York
New York State does not certify or license radon testers, and it does not certify or license radon mitigators. The Department of Health says testing firms may be certified by the American Association of Radon Scientists and Technologists (AARST), the National Radon Safety Board (NRSB), or New Jersey or Pennsylvania, and it lists the same bodies, plus the National Radon Proficiency Program, for mitigators (testers and mitigators). Anyone who analyzes the test must hold the Department of Health’s Environmental Laboratory Approval Program certification, and testing firms and mitigators must report results to the Department. The State’s Radon Task Force reported in 2023 that there are no training and experience or licensure/certification requirements for radon testing and mitigation professionals in NYS.
In practice that means a buyer has to do the checking. Ask the tester for a credential from one of those bodies and the number, ask which laboratory analyzes the kit and whether it holds the State certification, and ask for the report in writing. A home inspector’s State license does not cover radon; see how to check a home inspector’s license for what it does cover. If you are weighing which tests belong in your purchase, read which add-on tests you need. The site also has a page on radon testing; whoever you hire, ask the questions above.
Buying or selling: where radon enters the deal
- The seller’s form asks. The State disclosure form asks whether a radon test has been done and asks the seller to attach the report; it also says it is not a substitute for any home, pest, radon or other inspections or testing. See property condition disclosure. A prior result is useful, but its date, the floor tested and the lab matter.
- Timing belongs in the contract. A short-term test takes days and the lab takes more. Ask your attorney whether the contract timeline leaves room for it and for a second test, and see the inspection process for how the visits fit together.
- Basement apartments have a stricter number in New York City. The Health Department’s rules for basement and cellar apartments and accessory dwelling units legalized under Local Laws 126 and 127 of 2024 require a radon level below 2 pCi/L, half the usual action level. They also require testing by a certified radon testing professional with a device approved by the National Radon Proficiency Program or equivalent, analysis by a laboratory certified by the State, and they decline to accept over-the-counter kits for that certification. If a lower level is rented, or may be, ask what approvals it has; see certificates of occupancy and permits.
- Radon and water share a room, not a cause. A radon result says nothing about leaks, and a dry basement says nothing about radon. For the water side, see basement water after heavy rain.
A worked example
Another illustration, not a case we handled. A buyer is considering a 1950s split-level in Lewisboro, Westchester, with a finished lower level used as a den. The seller’s disclosure says no radon test has been done. In the State’s kit results 29 of 86 Lewisboro basements tested at or above 4 pCi/L, against 17.5% across Westchester, but neither is a result for this house. The buyer asks the attorney to allow time for a short-term test on the lower level with a credentialed tester, with a second test if the first is 4 pCi/L or higher. The report arrives in writing, with the laboratory named. The number from the house, not the number for the county, drives the next step.
For place-specific detail start with Westchester, Nassau, Suffolk, Staten Island, Queens, Brooklyn, the Bronx or Manhattan, and for the baseline read what a New York inspection includes.
Questions about radon in New York
What are the radon levels by county in New York?
In the State Health Department’s test-kit results, the share of basements at or above 4 pCi/L is 3.7% in Queens, 10.2% in Brooklyn, 12.2% in Manhattan, 7.9% in the Bronx, 6.3% on Staten Island, 5.7% in Nassau, 7.6% in Suffolk and 17.5% in Westchester. These are kit results since 1987, not a random sample of homes.
Do I need a radon test if my county is in EPA’s low zone?
Yes, EPA says all homes should be tested regardless of zone. The State’s kit results include Westchester basements at 4 pCi/L or higher in a Zone 3 county, and the Wadsworth Center says it is prudent to measure even where indoor radon is below average.
Does a home inspector test for radon?
Not as part of a home inspection. The State’s definition says a home inspection shall not include an inspection for radon or pests, so radon is a separate test by a separate tester. Ask any tester for a credential from AARST or NRSB and the name of the laboratory.
How long should a radon test run?
EPA says short-term tests stay in the home from two days to 90 days depending on the device, and long-term tests more than 90 days. A long-term test is more likely to show the year-round average. EPA suggests a short-term test first and a follow-up if the result is 4 pCi/L or higher.
Who is certified to test or fix radon in New York?
The State does not certify or license radon testers or mitigators. The Department of Health points to certification by AARST, NRSB, New Jersey or Pennsylvania, and requires the laboratory to hold its Environmental Laboratory Approval Program certification. Ask for the credential and check it.
Is radon only a basement problem?
No. Basement results run higher on average, but first-floor tests at or above 4 pCi/L appear in every area in the table, from one of 118 in Queens to 42 of 799 in Westchester. EPA says to place the test in the lowest lived-in level of the home.
About the figures
County and town radon figures are cumulative NYS Department of Health Radon Program test-kit results from 1987, from the open data files updated in November 2025. They are not for a single year, and the Department notes they may not reflect all tests in the State. Other figures are attributed in the text.
Testing before you close
If radon is on your list, plan the test early and ask your attorney about the timeline. For the inspection itself, tell us what worries you, and we will say plainly what it will and will not cover. Booking covers the five boroughs, Nassau, Suffolk and Westchester, and other areas on request. We speak English, Urdu, Punjabi and Hindi.
To talk it over first, call 718-925-7071.