Radon Testing
A continuous radon monitor placed on the lowest level you live in, for at least 48 hours of hourly readings, with a written report the day we collect it. Serving Northern Virginia, Maryland and Washington DC. Book online in a couple of minutes, or ask for a price first.
Why test for radon at all?
Because nothing else tells you. Radon has no smell, no color and no early symptoms, and it moves up out of the ground into the lowest rooms of a house. The only way to know what your home holds is to measure it.
No. 2cause of lung cancer
The second leading cause of lung cancer in the United States, after smoking, according to the EPA and the Surgeon General.
21,000deaths a year
The EPA's estimate of lung cancer deaths caused by radon in the United States each year.
1 in 4Fairfax County tests at or above 4.0
Of the radon tests reported to the Virginia Department of Health from Fairfax County, about one in four came back at or above the EPA action level.
The house next door does not predict yours. Levels vary from one home to the next, even on the same street with the same builder, because the soil, the foundation and the way the house breathes are all different. That is why the EPA's advice is the same for every home, in every zone: test it.
One test, two short visits, one price
A continuous radon monitor, placed and collected by an NRSB-certified technician. No laboratory and nothing to mail: you have the written result the day we pick the monitor up.
Day 1
Drop-off
We place the monitor
A technician sets the monitor on the lowest level you live in, the basement in most homes, away from drafts and windows. You get a two-hour arrival window. Adding radon to a home inspection puts this inside the inspection visit, so there is nothing extra to arrange with the seller.
48 hours
The house stays closed
The monitor does the work
A radon reading every hour, with temperature, humidity and pressure logged beside it. You live normally with the windows and exterior doors shut. The 48 hours is the testing protocol, not a preference, and the hourly record is what proves the house stayed closed.
Day 3
Pick-up and report
We collect it, read it, and write it up
A technician picks the monitor up on a weekday, in another two-hour window, and pulls the full record from it on the spot. The written report reaches you the same day. A test dropped off on a Monday is normally reported on the Wednesday.
NRSB-certified technicians. Our own team, certified by the National Radon Safety Board, not a subcontractor.
ANSI/AARST protocols. Placement, duration and closed-house conditions follow the national measurement standard.
Continuous monitors. Airthings Corentium Pro instruments, logging every hour for the whole test.
What your number means
Radon is measured in picocuries per liter, written pCi/L. One number in the report decides what happens next: the average over the whole test. The EPA sets the line at 4.0.
Below 2.0pCi/L
Low
No action is recommended. Test again after a major renovation, after finishing a basement, or before you sell.
2.0 to 3.9pCi/L
Elevated
Below the action level, but the EPA says to consider reducing it. There is no known safe level of radon, and the risk climbs with the number and the years spent breathing it.
4.0 and aboveEPA action level
Fix the home
The EPA and the Surgeon General recommend reducing radon in any home at or above 4.0. A mitigation system usually brings a house well under 2.0, and we re-test afterwards to prove it.
Source: U.S. Environmental Protection Agency, A Citizen's Guide to Radon.
Five things in every report
Written for the person who has to act on it. Nothing needs decoding, and it is yours to hand to a buyer, a seller, an agent or a landlord.
- 01Hourly readings for the entire test, charted, so you can see whether the level was steady or swung with the weather.
- 02The high and the low, which show the full range the house went through.
- 03The average, the single number the EPA action level applies to.
- 04Temperature, humidity and pressure across the same hours, which is how a test proves the house stayed closed.
- 05What to do next, in plain words, matched to your result.
Getting the house ready
A short-term radon test runs under closed-house conditions. The rules are simple, and they are what make the number trustworthy. We go through them again when we book you, and a seller gets the same list from the agent.
Close up 12 hours before
Windows and exterior doors stay closed from 12 hours before drop-off until the monitor is collected. Normal coming and going through doors is fine.
The lowest level you live in
We place the monitor in the basement or on the lowest floor you use regularly, where radon enters. Not a crawlspace, not a closet, not the kitchen counter.
Keep the house at a normal temperature
Heat or air conditioning on their usual settings, roughly 67 to 77°F. A house that swings hot or cold changes how air moves, and that shows up in the readings.
Leave the monitor where it is
Moving it, even to vacuum, can invalidate the test and mean starting the 48 hours again. If something has to change, call the office before touching it.
Fans, fireplaces and window units
Fans near the monitor off, ceiling fans on other floors fine. No fireplace or wood stove unless it is your main heat. Whole-house fans and window units that pull in outside air stay off, and central air stays on Auto.
Then live normally
Cook, shower, run the dryer, have people over. The test is measuring the house as you live in it, with the outside kept out. A radon system that is already installed stays running.
Where we test, and what the ground does there
The same $185 test everywhere we work. What differs is the ground under the house. The EPA map is a rough guide at best, and a low-risk zone has never cleared a single home; only a test does that.
Northern Virginia
Fairfax, Stafford, Clarke and Frederick counties are EPA Zone 1. Loudoun, Prince William, Arlington and Fauquier are Zone 2.
The map undersells Loudoun. It is rated Zone 2, yet the Virginia Department of Health's own results put Loudoun's average at 4.1 pCi/L, above the action level, with 31% of tests at or above 4.0. That is worse than Zone 1 Fairfax on both counts.
Counties we cover
Maryland
Montgomery, Howard and Frederick counties are EPA Zone 1. Prince George's, Anne Arundel and Charles are Zone 2.
The higher-potential counties sit on the Piedmont rock west and north of the Beltway; the coastal-plain counties to the east are rated lower. Neither rating clears a house, which is why Montgomery County requires the test at sale instead of trusting the map.
Counties we cover
Washington DC
The EPA rates the District Zone 3, its lowest category.
The lowest zone still tests high one time in nine. About one in nine radon tests logged by the District's own environment agency since 2019 came back at or above 4.0 pCi/L. Zone 3 is a prediction; those are measurements.
Coverage
The whole city, river to river.
Every neighborhood in the District, from Georgetown to Anacostia. See our Washington DC page
Somewhere nearby but not on the list? Call (703) 450-6398 and ask. Radon is one of eight environmental tests we run alongside mold and air quality; the full set is on the environmental services page.
Zones: EPA Map of Radon Zones, county data file. Loudoun and Fairfax figures: Virginia Department of Health radon program. District figure: DOEE radon test dataset, 2019 to March 2026, a share of tests rather than of homes.
We test. We never sell the fix.
NextDay Inspect installs no radon mitigation systems, so there is no version of your number that pays us better than another. If the result is 4.0 or above, you take the report to any licensed mitigation contractor you choose, and we come back afterwards to re-test independently, which is the one job the installer cannot honestly do for itself.
- Paid the same whether the number is 1.2 or 12
- No quote for a system, no installer who pays us for the introduction
- Independent re-test after any system somebody else installs
Radon testing, answered straight
The questions people actually ask us, answered without the hedging.
How much does radon testing cost?
A radon test is $185 on its own and $175 when it is added to a home inspection, and the price is the same in Virginia, Maryland and Washington DC. That covers a continuous radon monitor in place for at least 48 hours, drop-off and pick-up by an NRSB-certified technician, and the written report. Agents sometimes call it a radon inspection; it is the same test.
How long does a radon test take, and does it fit my inspection period?
The monitor stays in the home for a minimum of 48 hours, and you have the written result the day we collect it. Drop-off and pick-up each get a two-hour arrival window, with pick-up scheduled on a weekday, so a test started on a Monday is normally reported on the Wednesday.
That fits inside a typical inspection contingency. Adding radon to the home inspection puts the drop-off inside the inspection visit, so there is one fewer appointment to arrange with the seller.
Do I need to be home for the drop-off and the pick-up?
Not necessarily, but both visits need a way in. You, someone you trust, or lockbox or agent access arranged when you book, the same as for an inspection. For a home you are buying, the listing side usually handles access for the inspection visit, and the pick-up is arranged the same way.
What does 4.0 pCi/L mean, and what happens if my result is higher?
4.0 picocuries per liter is the EPA action level: at or above it, the EPA and the Surgeon General recommend reducing the radon in the home. Between 2.0 and 3.9 the EPA says to consider reducing it, because there is no known safe level.
Reducing it usually means a mitigation system, a sealed pipe and a quiet fan that draw air from under the slab and vent it above the roof, installed by a licensed mitigation contractor. We do not install them, so we have no stake in your number. Once a system is in, we come back and re-test independently to confirm it works.
Can I just use a DIY radon kit?
For a first look at your own home, yes, and it is better than not testing. A charcoal kit gives you one number for the whole period, it is sensitive to humidity, and it has to survive the mail to a laboratory before you learn anything.
A continuous monitor records every hour along with temperature, humidity and pressure. That hourly record is what shows whether a window was opened, which is why it is what a real estate transaction, a landlord or a county requirement normally asks for.
Does the time of year matter?
A test is valid in any season as long as the house stays closed up. Radon tends to run higher in winter, when the heating is on and the house is sealed, and lower in months when people live with the windows open, which is one reason the protocol calls for closed-house conditions rather than a particular month.
If a summer result came back under 2.0 and you have since finished the basement or moved a bedroom downstairs, it is worth testing again.
My house is new, or already has a radon system. Do I still need to test?
Yes. New homes in the District, and across Maryland, are built with passive radon-resistant construction, which is piping and a sealed slab. That is a building feature, not a measurement, and the only way to know it is doing anything is to test the finished house.
A home with an active system should be re-tested at least every two years, and after any work on the system, the foundation or the heating and cooling. The fan can fail quietly, and nothing about the house will tell you.
Is the report accepted for a home sale or a rental?
Yes. The report comes from a technician certified by the National Radon Safety Board, using a continuous monitor with the full hourly record attached, which is the form a buyer, seller, agent, landlord or county requirement expects. Because we do no mitigation, it also comes from a party with nothing to gain from the number.