How to Test for Radon in Colorado

You can't smell radon. You can't see it. You can't tell from looking at your house whether your level is 0.8 pCi/L (safely below the action threshold) or 12.4 pCi/L (well above it). The only way to know is to test.

In Colorado, that's not a small thing. CDPHE estimates roughly half of Colorado homes test above the EPA action level of 4.0 pCi/L. In El Paso County, more than 40% of homes tested between 2005 and 2023 came back elevated.^[1][2] This is the plain-language guide to testing your home — what kind of test to use, where to put it, what your result means, and when to retest.

1. Short-term DIY kit (2 to 7 days)

A small activated-charcoal or alpha-track canister you place in the lowest livable level of your home, then mail to a lab. Cost is typically $15–$40 including lab analysis. Results come back in 1–2 weeks.

Use a short-term test when:

• You want a quick first read on your home.
• You're in a real estate transaction with a tight timeline (though a professional test is preferred — see below).
• You're confirming the result of a previous test.

2. Long-term DIY kit (90+ days)

An alpha-track detector that sits in place for at least 90 days. Long-term tests average radon levels across seasons, which matters in Colorado because winter levels (sealed-up homes, stronger stack effect) are typically higher than summer levels. A 90-day or year-long test gives a more accurate picture of your average exposure than a 2-day snapshot.

Use a long-term test when:

• You're not under a transaction deadline.
• You want a more accurate annual exposure picture.
• A short-term test was borderline (close to 4.0 pCi/L).

3. Professional measurement (continuous monitor)

A continuous radon monitor placed by a DORA-licensed, NRPP or NRSB certified professional. Records hourly readings; results typically returned in 48–72 hours. The standard for real estate transactions and any situation requiring a defensible result.

Use professional measurement when:

• You're buying or selling a home and need a defensible result.
• Your DIY test came back high and you want a third-party confirmation before mitigation.
• You're testing after mitigation (a post-mit test).

Professional measurement in Colorado Springs typically runs $150–$300. Full real-estate-testing walkthrough →

• El Paso County Public Health Laboratory. Short-term kits $15, long-term $42. Pickup at 1675 W. Garden of the Gods Rd, Colorado Springs. Phone (719) 578-3199 option 3.^[2]
• CDPHE state radon program. Periodically offers low-cost or free kits during National Radon Action Month (January). Check cdphe.colorado.gov/radon.^[1]
• Retail hardware stores. Home Depot, Lowe's, Ace Hardware, and Amazon stock EPA-listed short-term kits. Look for "EPA-listed" or "AARST-NRPP listed" on the packaging — these are the kits backed by accredited labs.
• Online radon labs. Many ship a canister and pre-paid return mailer with lab analysis included in one price.

A test placed incorrectly returns the wrong answer. The EPA placement guidance:^[3]

• Place the test in the lowest livable level of the home (a finished basement counts; an unfinished crawlspace does not).
• Place it 2–6 feet above the floor, away from drafts, fireplaces, exterior walls, and high-humidity areas like bathrooms.
• Keep windows and exterior doors closed for at least 12 hours before and during a short-term test. Normal in-and-out traffic is fine.
• Avoid placing the test next to running HVAC vents or in direct sunlight.
• Don't move the test once it's deployed.

Detail: where to place a test →

Result (pCi/L)	EPA guidance	What to do
< 2.0	Below "consider action" threshold	Retest every 2 years.
2.0–3.9	EPA suggests "consider mitigation"	Retest (long-term preferred) and decide. Many Colorado homes in this range still mitigate, because WHO recommends action at 2.7 pCi/L.
4.0 or above	Action level — mitigate	Confirm with a second test or a professional continuous monitor. Then get at least two written quotes from DORA-licensed Colorado contractors.
10.0 or above	Well above action level	Mitigate. Limit time in the lowest level until a system is in place.

Action level reference: EPA — Health Risk of Radon. WHO reference: WHO Guidelines for Indoor Air Quality (2010).

If you tested in the borderline range — say, 3.7 pCi/L or 4.1 pCi/L — you're not alone in feeling stuck. Most Colorado homeowners in this band wrestle with the same decision.

A few things to know:

• The EPA's 4.0 action level isn't a cliff. Risk is continuous. 3.9 pCi/L and 4.1 pCi/L are essentially the same exposure.
• WHO recommends action at 2.7 pCi/L, which is significantly lower than EPA. Many international guidelines fall in the 2.7–4.0 range.
• Colorado has significant seasonal swings. A short-term winter test reading at 3.7 may show 2.4 in summer, or vice versa. A long-term test (90+ days) averages across seasons.
• Risk is exposure-time dependent. Daily use of the lowest level (a finished basement bedroom, a home office) matters more than time spent on upper floors.

The decision tree most homeowners settle on:

1. Run a long-term test for 90 days to get the seasonal average.
2. If the long-term result is also above 3.5, most people mitigate — particularly if the lowest level is used daily.
3. If the long-term result drops below 3.0 and the lowest level isn't heavily used, retesting every 2 years is a reasonable choice.

• Every 2 years for a previously low result. EPA standard recommendation.^[4]
• After any major remodel that changes the foundation, basement, or HVAC.
• After mitigation — a post-install test confirms the system actually brought levels below 4.0 pCi/L.
• Before listing or buying a home.
• If your living patterns change — for example, finishing a basement that becomes daily living space.