Whats Radon Testing: A Plain-Language Guide
This is the article for the homeowner who has just heard the word “radon” for the first time and is wondering what radon testing actually is. The answer matters because Colorado sits in EPA Zone 1 — the highest-radon-risk zone in the country — and CDPHE estimates about half of tested homes statewide read above the federal action level. This guide starts from zero: what radon is, why it matters, and what testing looks like. The information reflects EPA and CDPHE guidance current as of 2026 — consult a licensed mitigation professional for elevated results and your physician for any health concerns.
Part of our Radon Levels guide — start there for the full picture →
Whats Radon Testing: The Beginner Answer
Radon testing is the process of measuring the concentration of radioactive radon gas inside a home and comparing the result to the EPA’s action level of 4 pCi/L. The gas is colorless, odorless, and chemically inert — humans cannot smell or see it. It seeps from soil into homes through cracks in foundations, slab-wall joints, sump pits, and plumbing penetrations. Long-term exposure is the second leading cause of lung cancer in the United States after smoking. Testing identifies whether a home has a problem; mitigation fixes it. The whole testing cycle costs $15 to $250 depending on method and takes 3 to 12 days from purchase to result.
What Radon Actually Is
Radon is a naturally occurring radioactive element — element 86 on the periodic table. It is a noble gas, like helium or argon, meaning it does not chemically bond to other atoms. Radon-222, the relevant isotope for indoor air quality, has a half-life of 3.8 days. It forms from the radioactive decay of uranium and radium, both of which exist in trace amounts in nearly all soils, rocks, and groundwater. Colorado’s bedrock has higher-than-average uranium content, which is why the EPA designates the state as Zone 1.
As radon decays, it produces a sequence of short-lived radioactive daughter products: polonium-218, lead-214, bismuth-214, and polonium-214. These daughters emit alpha particles that can damage lung tissue when inhaled and deposited in the airways over years of exposure. The EPA estimates radon causes about 21,000 lung cancer deaths in the United States annually.
Why Indoor Radon Is a Concern
Soil gas containing radon migrates upward through the ground and into buildings driven by pressure differentials. Homes are usually slightly negatively pressured relative to the ground beneath the slab — particularly in winter when warm air rises and creates a “stack effect” that pulls soil gas in. The radon enters through any opening: foundation cracks, the joint where the slab meets the wall, sump pit perimeters, plumbing penetrations, and gaps around vent stacks.
Outdoors, radon dilutes quickly to background concentrations around 0.4 pCi/L. Indoors, in a tight modern home in winter, it can concentrate to 20, 40, or even 100 pCi/L. Colorado’s combination of high baseline uranium content and tight modern construction puts the state at the highest end of the national radon distribution. The pillar guide on radon testing in Colorado covers state-level context.
What the Numbers Mean
Radon concentration is measured in picocuries per liter (pCi/L). A picocurie is one trillionth of a curie, which is itself a measure of radioactive decay events per second. At 4 pCi/L, the EPA estimates lifetime exposure produces about a 1-in-200 chance of dying from radon-induced lung cancer for non-smokers, or 1-in-25 for smokers. The action level reflects what the EPA considers an actionable risk threshold given realistic mitigation costs and effectiveness.
Below 2 pCi/L the home is in the lower-risk band. Between 2 and 4 pCi/L is the consideration range. At or above 4 pCi/L the EPA recommends mitigation. No level is considered risk-free, but the standard inflection point is 4 pCi/L.
Why You Cannot Just Smell It
Radon-222 is a noble gas. Noble gases by definition do not react chemically and do not have an odor. At indoor concentrations of a few pCi/L, only a few hundred radon atoms exist in any liter of air at any moment. Even strongly-smelling molecules cannot be detected at that concentration; for a noble gas with no odor at any concentration, smell detection is physically impossible. Sight fails for the same reason — the gas is invisible at all relevant concentrations. The in-batch how do you test for radon gas guide explains the detection science.
How Testing Works in Plain Language
Method 1: Charcoal Canister
A small canister filled with activated charcoal is opened in the basement for 48 to 72 hours. The charcoal absorbs radon. The canister is sealed and mailed to a lab, which counts the radioactive decay products and back-calculates the average radon concentration during the exposure window. Cost: $15 to $30 including lab analysis. Result in 5 to 10 business days after shipping.
Method 2: Alpha-Track Detector
A small piece of polymer film inside a plastic housing is left in the home for 90 days to one year. Alpha particles from radon decay create microscopic damage tracks in the film. The lab etches the film and counts the tracks. Cost: $25 to $50. Best for an annual-average reading.
Method 3: Continuous Radon Monitor
An electronic device that reads radon hourly. Professional models cost $1,200 to $5,000 and are used by licensed measurement specialists for real-estate transactions. Consumer models cost $150 to $300 and provide ongoing visibility for personal use.
The in-batch how is radon tested methodology guide compares these methods in detail.
Who Should Test
Every home in EPA Zone 1 should be tested at least once and re-tested every two years thereafter. Colorado is entirely in Zone 1, so essentially every Colorado home is in scope. The EPA also recommends testing whenever a home is being bought or sold, after major construction changes, and any time a previously unmitigated home is reoccupied after vacancy. The in-batch who should test for radon guide covers occupancy-specific triggers.
DIY vs Professional Testing
A homeowner buying a DIY kit for personal screening can run the test, mail the canister, and read the result without involving any professional. The cost is $15 to $50 for a kit. A buyer in a real-estate transaction needs a professional measurement specialist with a calibrated continuous radon monitor and EPA Protocols compliance. The professional test costs $135 to $200 bundled with a home inspection. Both methods produce a pCi/L result; the difference is documentation and credential weight. The in-batch DIY radon testing decision framework explores this in depth.
What Happens After Testing
If the result is below 4 pCi/L the homeowner notes the result and re-tests in two years. If the result is at or above 4 pCi/L the homeowner commissions a confirmatory test (the EPA wants two short-term tests averaging above 4 pCi/L or one long-term test above 4 pCi/L before mitigating). Once confirmed, the homeowner calls a Colorado-licensed mitigator.
The standard mitigation system on the Front Range is active sub-slab depressurization: a 4-inch PVC pipe drawn through the basement slab into the soil-gas layer, an inline fan in the attic or garage, and a vent stack terminating above the roofline. The fan runs continuously and reverses the pressure differential, pulling soil gas out before it enters the home. Front Range install costs typically run $1,200 to $2,500. The in-batch home radon mitigation system guide covers installation.
Common Misconceptions
“Radon is only in older homes.” False. Modern construction can be tighter, which sometimes increases concentrations because there is less natural air exchange to dilute soil gas.
“I would smell it if I had it.” False. Radon is a noble gas with no odor at any concentration.
“My neighbor tested low so I am fine.” False. Radon varies house-by-house even on the same block because foundation construction, soil porosity, and building tightness all differ.
“It is only a basement problem.” Partially true — basements typically show the highest concentrations, but radon also rises through the home and exposure occurs on every floor where occupants spend time.
Why Colorado Specifically
Colorado’s bedrock — particularly along the Front Range — contains relatively high uranium content compared to many other U.S. regions. Uranium decays through radium to radon-222, and the resulting soil gas migrates upward into homes. Colorado is in EPA Zone 1, the highest-risk designation. All Colorado counties are in Zone 1 status. The combination of bedrock geology, sealed modern construction, and Front Range winter stack-effect dynamics produces the elevated indoor radon prevalence CDPHE has documented.
CDPHE has run public-awareness campaigns for two decades on Front Range radon. The state public health department distributes discounted or free DIY kits through county public health offices on a rotating basis. The agency also maintains a public list of licensed mitigators and measurement specialists.
What a Test Kit Looks Like in Your Hand
A typical short-term charcoal canister kit is the size of a small can of tuna. The canister contains activated carbon and is sealed inside a foil pouch. The kit ships with a printed chain-of-custody form, instructions, and a prepaid lab-return envelope. Total weight: a few ounces. Cost at a Front Range hardware retailer: $15 to $30 including lab analysis. Brands seen on Colorado shelves include Air Chek and AccuStar most commonly.
Opening the foil pouch starts the test. The canister is placed in the designated room per the placement rules. Closing the canister at the end of the test window stops it. The prepaid envelope goes to the post office. Email confirmation arrives when the lab receives the kit. Result email arrives 5 to 10 business days later.
What Happens If You Find Radon
Finding radon is not an emergency. The risk is from cumulative exposure over decades, not days or weeks. A homeowner whose test reads 8 pCi/L has time to commission a confirmatory test, get quotes from two or three Colorado-licensed mitigators, and schedule an install on a reasonable timeline. The typical mitigation timeline from confirmed elevated reading to verified post-install reading is 30 to 60 days. The in-batch what is radon testing in homes guide walks the full decision tree.
Cost of Testing vs Cost of Ignoring
A short-term DIY kit costs $20. Two seasonal short-term tests across a year cost $40. A long-term alpha-track costs $35. A pro CRM test bundled with home inspection costs $135 to $200. The total cost of comprehensive testing across a Colorado home’s first year of ownership is rarely more than $300.
The cost of ignoring radon is harder to quantify but is real. The EPA estimates radon causes about 21,000 U.S. lung cancer deaths annually. Mitigation, if needed, runs $1,200 to $2,500 — small relative to the cost of treating a lung cancer diagnosis decades later. The math heavily favors testing.
References
- A Citizen’s Guide to Radon — U.S. Environmental Protection Agency
- Colorado Radon Program — Colorado Department of Public Health and Environment
- About Radon — Centers for Disease Control and Prevention
- Radon and Lung Cancer — American Lung Association
Frequently asked questions
What is radon testing in plain language?
Radon testing is the process of measuring how much radioactive radon gas is inside a home. The gas is colorless and odorless, so testing is the only way to know. Results are reported in picocuries per liter, and the EPA recommends mitigation at or above 4 pCi/L.
How does radon get into my home?
Radon forms from naturally occurring uranium in soil. Soil gas migrates upward through cracks in foundations, slab-wall joints, sump pits, and plumbing penetrations. Homes are slightly negatively pressured relative to the ground beneath them, which pulls radon in.
Why does Colorado have such a radon problem?
Colorado bedrock contains higher-than-average uranium content, which produces more radon. The state is in EPA Zone 1 — the highest-risk zone — and CDPHE reports about half of tested homes statewide read above the 4 pCi/L action level.
Is radon testing required by law?
No federal or Colorado law requires testing of an existing home. Real-estate transactions commonly include testing in the inspection contingency. Some new-construction local ordinances require post-build testing as a code compliance item.
Front Range homeowners new to radon and wanting a connection to a licensed local specialist can reach out through our contact page.
Test your home for radon
Radon is invisible and odorless, so a test is the only way to know your level. A short-term kit gives a first reading in days; a digital monitor tracks it over time.
| Product | Why | Buy |
|---|---|---|
 AirChek Charcoal Radon Test Kit | Lab fee usually included; EPA short-term protocol. | Amazon — $21.95 |
 First Alert RD1 Radon Test Kit | Widely stocked; 48-hour charcoal test. | Amazon — $16.98 |
 Airthings Corentium Home | Digital monitor with a long-term average. | Amazon — $147.14 |