Buying a home comes with a long list of decisions. Home inspection, well and septic inspections, water testing, sewer scopes, mold concerns—the list can grow quickly.
So when someone asks, “Do I really need a radon test?”, sometimes what they are actually asking is:
“Is radon testing required?”
Those are two very different questions.
In most of Maryland, a radon test is not currently required simply because a home is being sold. Montgomery County has its own requirements for certain residential real-estate transactions, but Maryland does not have a statewide point-of-sale radon testing requirement.
That does not mean radon testing is unnecessary. And this brings us to our very first important remark:
Not required does not mean not necessary.
What Is Radon, and Why Does It Matter When Buying a Home?
Radon is a naturally occurring radioactive gas produced by the breakdown of uranium in soil and rock. It is invisible, odorless, and tasteless, so you cannot determine whether a home has elevated radon by looking at the property—or by performing a standard home inspection.
According to the U.S. Environmental Protection Agency, radon is the leading cause of lung cancer among people who do not smoke and is responsible for an estimated 21,000 lung cancer deaths in the United States each year.
The EPA recommends taking action to reduce radon levels when a home's measured concentration is 4.0 picocuries per liter (pCi/L) or higher and recommends considering action for levels between 2.0 and 4.0 pCi/L.
I usually tell my clients: “If this were my house, I would invest in fixing any number above 2.0.”
That goes beyond simply asking what the regulatory action level is. It is about understanding the risk and making an informed decision about the home where you are going to live.
Most importantly for a homebuyer, radon levels can vary significantly from one home to another.
The house next door having a low radon result does not tell you the radon concentration in the house you are buying.
The only way to know is to test.
Is Radon Testing Required When Buying a Home in Maryland?
Generally, no—not statewide.
Maryland's residential property disclosure process addresses radon information, but Maryland does not currently require every home to receive a radon test as part of a residential real-estate transaction.
There is also an important development underway.
In 2026, the Maryland Real Estate Commission approved a revised Residential Property Disclosure/Disclaimer form that includes an additional question addressing whether a home has been tested for radon. As of August 2026, the revised form has been approved and is moving through the implementation process.
That is a meaningful step.
Asking about a property's radon testing history puts radon into the conversation between sellers and buyers and may help uncover information that otherwise would not have been discussed.
But there is an important distinction:
Asking whether a home has been tested is not the same as requiring the home to be tested.
And a previous test result is not necessarily a measurement of the home's current radon concentration.
Disclosure Is Not the Same as Measurement
Suppose a seller answers that the home was previously tested for radon.
That's useful information.
But the next questions should be:
When was it tested? What was the result? How was the test performed? Has anything about the property changed since then?
A radon result represents the conditions during a particular measurement period.
Homes are not static. HVAC systems can be replaced. Foundations can be modified. Basements can be finished. Additions can be built. Drainage and soil conditions can change. Radon mitigation systems can be installed, modified, damaged, or simply age.
Even without major renovations, radon concentrations can fluctuate over time.
That is why a historical radon result and a current radon measurement answer different questions.
Disclosure asks: Has this home been tested?
Current measurement asks: What is the radon concentration in this home now?
For a buyer making a decision about a property today, the second question matters.
Montgomery County Is Different
If you are buying a home in Montgomery County, Maryland, different requirements may apply.
Montgomery County requires radon testing in connection with the sale of certain single-family homes. The County's requirements establish testing and disclosure obligations before settlement, with some properties and transactions excluded from the law.
This is an important distinction because Montgomery County does something Maryland does not currently do statewide:
It moves beyond simply asking what is already known about radon and requires an actual measurement for covered transactions.
If you are purchasing a property in Montgomery County, it is important to understand whether the property falls under the County's requirements and what testing documentation must be provided.
What If the Seller Already Has a Radon Test?
Don't automatically disregard it—but don't automatically rely on it either.
Look at the date of the test, the testing method, where the device was placed, who performed the measurement, whether required test conditions were maintained, and whether significant changes have occurred at the property since the measurement.
A properly performed recent test may provide valuable information.
A test performed many years ago under unknown conditions is a very different thing.
And if the property has a radon mitigation system, testing is still important.
The House Has a Radon Mitigation System. Do I Still Need to Test?
Yes.
A mitigation system tells you that someone previously addressed radon at the property. It does not tell you how the system is performing today.
Radon mitigation systems should not be treated as permanent proof that radon concentrations remain low.
The EPA recommends testing after a mitigation system is installed and periodically afterward. Testing is the way to verify that the system continues to reduce radon effectively.
For a homebuyer, a mitigation system should generally be viewed as a reason to verify performance—not a reason to skip testing.
What About New Construction?
A new house can have elevated radon too.
Radon is primarily related to the interaction between the building and the soil beneath and around it—not the age, cleanliness, price, or appearance of the home.
Even when radon-resistant construction techniques are used, testing after construction is the only way to determine the actual radon concentration inside the finished home.
“Brand new” and “low radon” are not synonyms.
Can I Use a DIY Radon Test When Buying a House?
Consumer radon tests can play an important role in radon awareness and routine homeowner testing.
A real-estate transaction, however, creates additional considerations.
There is usually a limited inspection period. The buyer does not control the property. Test conditions must be maintained. Device placement matters. Timing matters. Interference or unusual conditions may affect whether the measurement is representative or valid.
Professional radon measurement is not simply placing a device somewhere in the basement and returning two days later to read a number.
A qualified radon measurement professional should follow applicable ANSI/AARST radon measurement standards and protocols, document test conditions, select appropriate measurement locations and methods, and evaluate circumstances that could affect the validity of the test.
When a result may influence a significant financial and health-related decision, the quality of the measurement matters.
What Happens if the Radon Result Is 4.0 pCi/L or Higher?
First: don't panic.
An elevated radon result does not mean you should automatically walk away from the house.
Radon can be reduced.
The EPA recommends taking action when the measured radon concentration is 4.0 pCi/L or higher. A qualified radon mitigation professional can evaluate the property and determine an appropriate mitigation approach.
After mitigation, the property should be tested again to verify that the system is actually reducing the radon concentration.
That last step matters.
Installing equipment is not the same as verifying its performance.
Measurement identifies the problem. Post-mitigation measurement verifies the solution.
What If the Windows Were Open or the House Was Vacant?
Short-term radon measurements used in real-estate transactions require particular building conditions.
Under applicable ANSI/AARST measurement standards, closed-building conditions must be established before certain short-term measurements begin and maintained during the required measurement period. Normal entry and exit are expected, but leaving windows open, improperly operating ventilation equipment, moving a measurement device, or making other significant changes to building conditions can affect the measurement.
And here is something homebuyers may not realize: a problem with test conditions does not always mean the entire test has to be thrown away and started over.
Depending on what occurred, when it occurred, the measurement method being used, and whether compliant conditions can be re-established and documented, the measurement period may sometimes be extended so that the required compliant measurement period is achieved in accordance with the applicable ANSI/AARST standard.
That is one of the reasons professional oversight matters. The answer isn't simply, “Well, somebody opened a window, so I guess we're done.” The measurement professional has to evaluate what happened, document it, and determine the appropriate response under the standard.
An empty house is not automatically a problem.
An uncontrolled house can be.
So, Should You Test?
If you are buying a home in Maryland, the absence of a statewide requirement should not be the deciding factor.
The better question is:
Would you rather know the radon concentration before you own the house—or after?
Radon cannot be seen during a home inspection. It cannot be smelled. Your neighbor's result cannot tell you yours. A seller's lack of knowledge does not establish that elevated radon is absent. And an old test does not necessarily tell you what is happening today.
Maryland's upcoming revised disclosure question is a positive step because it encourages buyers and sellers to talk about radon testing history.
But awareness and measurement serve different purposes.
A disclosure can tell you what someone already knows.
A test gives you information about the home you are actually buying.
And until Maryland requires that measurement statewide:
Not required does not mean not necessary.
Professional Radon Testing in Maryland
Smart Home Inspects provides professional radon measurement as part of our environmental testing services throughout Montgomery, Prince George's, Howard, and Frederick counties and other selected areas of Maryland.
We are a testing-only company. We do not perform radon mitigation, allowing our role to remain focused on independent measurement and verification.
For more information, visit our Professional Radon Testing resources, learn how to prepare a property for a radon test, review Maryland and local radon requirements, or request professional testing for a property.
