Should I Test for Radon? A Front Range Decision Guide
For almost every Colorado Front Range homeowner, the honest answer is yes, and usually sooner than you think. The Colorado Department of Public Health and Environment estimates that roughly half of Colorado homes test above the EPA action level of 4 picocuries per liter (pCi/L). But “test everyone” is not a satisfying answer if you are trying to decide whether it is worth doing this month. This guide gives you a concrete way to place your own home on a spectrum from “test this week” to “you can reasonably wait,” using three inputs: where the house sits, how it was built, and who sleeps in it.
The short version
Radon is an invisible, odorless soil gas and the second leading cause of lung cancer in the United States after smoking, and the number-one cause among people who never smoked, according to the EPA and the CDC. Every county on the Front Range sits in EPA Radon Zone 1, the highest-risk tier, where the predicted average indoor level already exceeds the action level. If you live in Denver, Boulder, Jefferson, Douglas, Arapahoe, Adams, El Paso, Larimer, or Weld County and have not tested in the last five years, treat that as a yes.
What actually changes the answer
Your county’s radon zone sets a starting probability, not a verdict. The EPA Map of Radon Zones is built from survey averages, and homes on the same street routinely diverge wildly. One Zone 1 house measures 1.5 pCi/L while its neighbor two doors down reads 8, driven by foundation cracks, soil differences, sump pits, and how the furnace pulls air through the building. That is exactly why EPA recommends testing every home in every zone, including Zone 3. The map tells you the odds; only a test tells you the number. Our companion piece on what EPA radon zones actually mean breaks down the tiers if you want the full map logic.
Conditions that push you to “test now”
- You are in Zone 1 (all of the Front Range). No further justification needed.
- Anyone sleeps or spends hours below grade. Basement bedrooms, finished basements, and garden-level apartments concentrate radon two to four times more than the top floor of the same house.
- You are buying or selling. A transaction test gives the buyer baseline data and negotiating room, and it is cheap relative to the deal.
- The house predates the early 1990s. Many older slabs lack the under-slab polyethylene vapor barrier that later became standard, leaving more open soil-gas pathways.
- A current or former smoker lives there. Radon and tobacco smoke multiply each other’s risk. At 4 pCi/L, EPA estimates lifetime lung-cancer risk at about 62 in 1,000 for a smoker versus 7 in 1,000 for someone who never smoked; at 20 pCi/L the smoker figure climbs to roughly 26 in 100.
- Your last test is more than five years old. Levels drift as foundations settle, sealants age, soil moisture cycles, and HVAC systems get replaced. A 2020 reading is not a 2026 reading.
Conditions where you can slow down (but not stop)
If you are in a lower-risk Zone 3 county with all living space above grade, one careful test during heating season is enough; if it comes back under 2 pCi/L, retest every few years or after any major change. If a builder installed an active mitigation system with a running fan, confirm it works with a single 48-hour test, then switch to checking the fan’s status rather than re-testing on a schedule. Almost the only time skipping is defensible is an apartment above the third floor of a multi-story building, where the soil-gas pathway is negligible. Ground- and first-floor units should still test, because soil gas travels up elevator shafts and stairwells.
What the test itself involves
A first-pass screening test is genuinely simple. A passive 48-to-96-hour charcoal canister or an alpha-track kit costs $20 to $50 including lab analysis. Place it in the lowest occupied level, on a stable surface about 20 inches above the floor, away from drafts, exterior walls, and fans. Keep the house in “closed-house” conditions (windows and exterior doors shut except normal entry) for 12 hours before and throughout the test, then mail it to the lab in the prepaid envelope. Results arrive in about a week. Placement matters more than people expect; see our notes on where to put a radon test before you start the clock.
For a faster, harder-to-fool result, a continuous radon monitor logs hourly readings and flags interference such as an opened window. Homeowner-grade units run $200 to $300; a certified measurement professional deploys one for roughly $200 to $400 including the visit. Our overview of radon testing costs compares the options, and the radon testing hub covers the broader Colorado context.
Reading your result
| Result | What EPA says | Practical next step |
|---|---|---|
| 4 pCi/L or higher | Action level. Mitigation strongly recommended. | Get a mitigation quote; a fan-and-pipe system typically drops levels below 2. |
| 2 to 4 pCi/L | Consider mitigating. | Many Front Range owners mitigate anyway, especially with basement bedrooms, because winter closed-house levels swing higher. |
| Under 2 pCi/L | Generally acceptable. | Retest every few years or after renovation, foundation work, or an HVAC change. |
There is no threshold below which radon is provably harmless, which is why the guidance uses “action” and “consider” rather than “safe.” For the fuller reasoning behind the numbers, see what counts as a safe radon level, and if your reading lands high, our explainer on radon mitigation covers what a fix involves.
Why one-and-done testing falls short
A single measurement captures a single moment. Radon responds to season, barometric pressure, occupancy, and how hard the furnace runs, so a summer reading with the windows cracked can badly understate a January closed-house level. The most defensible long-term approach is to test short-term every couple of years in heating season, or leave a long-term alpha-track detector or continuous monitor in place. The right cadence depends on your first result and how much variability you want to track.
Frequently asked questions
The FAQ below answers the questions readers ask most after deciding whether to test.
This guide reflects EPA, CDC, and CDPHE guidance current as of 2026 and is not a substitute for testing your own home. Front Range homeowners ready to test can connect with a vetted radon measurement professional for a 48-hour closed-house test with chain-of-custody documentation.