Residential Radon Testing in Montgomery County, Maryland
Protect your home with a fast, professional 48-hour radon test. RADON & CO provides NRPP-certified residential radon testing for homeowners throughout Montgomery County, with select availability in DC, Northern Virginia, Howard County, and nearby areas.
See what we're actually finding nearby
Real average radon readings by zip code, built from our own NRPP-certified tests across the DMV — not an EPA zone estimate. Search your zip code or browse the map below.
Full data table, by zip code
| Zip Code | Area | Average Radon Level |
|---|---|---|
| 22312 | Alexandria | 1.40 pCi/L |
| 20861 | Ashton | 0.70 pCi/L |
| 20705 | Beltsville | 0.80 pCi/L |
| 20814 | Bethesda | 2.30 pCi/L |
| 20816 | Bethesda | 2.85 pCi/L |
| 20817 | Bethesda | 2.55 pCi/L |
| 20841 | Boyds | 1.87 pCi/L |
| 20833 | Brookeville | 1.50 pCi/L |
| 20866 | Burtonsville | 2.20 pCi/L |
| 20818 | Cabin John | 0.70 pCi/L |
| 20815 | Chevy Chase | 1.75 pCi/L |
| 20871 | Clarksburg | 2.36 pCi/L |
| 21045 | Columbia | 2.20 pCi/L |
| 21046 | Columbia | 1.10 pCi/L |
| 20872 | Damascus | 6.62 pCi/L — at/above EPA action level |
| 20855 | Derwood | 3.97 pCi/L |
| 21042 | Ellicott City | 2.20 pCi/L |
| 20155 | Gainesville | 0.90 pCi/L |
| 20877 | Gaithersburg | 1.78 pCi/L |
| 20879 | Gaithersburg | 1.60 pCi/L |
| 20882 | Gaithersburg | 4.38 pCi/L — at/above EPA action level |
| 20886 | Gaithersburg | 2.10 pCi/L |
| 20874 | Germantown | 1.42 pCi/L |
| 20876 | Germantown | 1.27 pCi/L |
| 20794 | Jessup | 5.80 pCi/L — at/above EPA action level |
| 20895 | Kensington | 1.55 pCi/L |
| 20878 | North Potomac | 1.82 pCi/L |
| 20832 | Olney | 1.33 pCi/L |
| 20837 | Poolesville | 1.20 pCi/L |
| 20854 | Potomac | 4.91 pCi/L — at/above EPA action level |
| 20850 | Rockville | 1.56 pCi/L |
| 20851 | Rockville | 1.50 pCi/L |
| 20852 | Rockville | 1.95 pCi/L |
| 20853 | Rockville | 2.87 pCi/L |
| 20901 | Silver Spring | 1.77 pCi/L |
| 20902 | Silver Spring | 2.36 pCi/L |
| 20903 | Silver Spring | 2.50 pCi/L |
| 20904 | Silver Spring | 4.10 pCi/L — at/above EPA action level |
| 20905 | Silver Spring | 5.70 pCi/L — at/above EPA action level |
| 20906 | Silver Spring | 2.27 pCi/L |
| 20910 | Silver Spring | 1.68 pCi/L |
| 20912 | Takoma Park | 2.30 pCi/L |
| 20009 | Washington | 0.30 pCi/L |
| 20011 | Washington | 2.17 pCi/L |
Full write-up, methodology, and data-use terms on the dedicated Radon Levels Map page →
Why homeowners test for radon
Radon levels can vary from home to home, even within the same neighborhood. A neighbor's result does not tell you your home's radon level. The only way to know the radon level inside your home is to test. That's especially true in Montgomery County, which the EPA maps as Radon Zone 1 — its highest-risk category, meaning the county's predicted average indoor screening level exceeds the EPA's own action threshold of 4 pCi/L. That's a countywide geological classification, not a prediction about any single house, which is exactly why the zone designation is a reason to test, not a substitute for it.
What "closed-house conditions" actually means
A professional radon test only means something if the building was in closed-house conditions before and during the test. Following ANSI/AARST protocol, that means all exterior windows and doors stay closed except for normal, momentary entry and exit, for at least 12 hours before the test begins and for the full duration of the test; the thermostat stays at a normal, occupied setting; and whole-house fans, fireplaces, and wood stoves aren't run during the window. That's a real constraint on the household, not a formality — testing without it produces a reading that doesn't reflect how the home actually behaves day to day, which is why RADON & CO reviews these conditions with you before scheduling.
What is included
- Professional digital monitor placement
- 48-hour measurement period
- Pickup after the test window
- Electronic report for your records
- Clear next-step explanation if results are elevated
Pricing
Montgomery County residential radon testing is a flat $125. Extended service areas are priced by distance: $175 for Howard County, North DC, Arlington, and Frederick City/Urbana; $200 for South DC, Fairfax County, and outer Frederick County; $225 for Loudoun and Prince William counties. See full pricing by area.
Professional testing vs DIY kits
DIY kits can be useful for screening, but a professional test gives you a cleaner process, trained placement, digital monitor workflow, and an electronic report that is easier to use for records or a future real estate transaction. It also matters if you're selling: Montgomery County's pre-sale radon law and the region's standard real estate radon contingency both have specific requirements about who can perform the test, which a hardware-store kit doesn't satisfy — see our full comparison of professional testing vs. DIY kits for the details.
Frequently asked questions
How long does a professional radon test take?
Most short-term professional radon tests run for at least 48 hours. RADON & CO places a digital continuous radon monitor, retrieves it after the test window, and provides a clear electronic report.
How much does residential radon testing cost?
Residential radon testing is $125 flat in Montgomery County. Extended service areas are priced by distance: $175 for Howard County, North DC, Arlington, and Frederick City/Urbana; $200 for South DC, Fairfax County, and outer Frederick County; $225 for Loudoun and Prince William counties.
Do you test for real estate transactions?
Yes. RADON & CO is built for real estate timelines and can coordinate with agents, authorized access, closed-house conditions, and electronic reporting.
Do you test commercial properties?
Yes. RADON & CO supports commercial radon testing for multifamily buildings, nursing homes, assisted living facilities, schools, childcare centers, property portfolios, and HUD-related projects.
Do you provide mitigation?
No. RADON & CO specializes exclusively in independent radon testing. If elevated radon levels are detected, we can help explain your results and recommend contacting a qualified radon mitigation professional. To avoid conflicts of interest, NRPP-certified radon measurement professionals are not permitted to perform mitigation on properties they test.