Denver radon test kit questions, answered first

Radon is a radioactive gas that forms as uranium in soil breaks down. You cannot see it, smell it, or taste it, and it does not give you a same-day symptom you can use as a warning. CDPHE cites the Surgeon General: radon is the second leading cause of lung cancer in the United States, after smoking. EPA estimates about 21,000 radon-related lung cancer deaths a year. The practical response is a test of the house, not a guess from the year it was built.

Because Denver County is EPA Zone 1, and because a zone is not a result. CDPHE says Colorado soils carry high radon potential and that you should test even if a mitigation system is already installed. A mail-in kit is the cheapest, simplest way to learn whether your lowest lived-in room is near the 4.0 pCi/L action level. The test is about the slab, the sump, and how the house is run, not about the neighborhood’s reputation.

Denver, Adams, Arapahoe, Jefferson, Douglas, Boulder, and Broomfield Counties are Zone 1 in the EPA Map of Radon Zones data file (June 2024). Zone 1 means a predicted average indoor screening level above 4 pCi/L. CDPHE says about half of Colorado homes test above 4 pCi/L, and that high levels occur in every part of the state. Use that as a reason to test. Do not use it as a stand-in for your address. This guide does not invent neighborhood averages.

4.0 pCi/L is the level at which EPA says to fix the home. Between 2 and 4, EPA says to consider fixing. Levels under 4 are not a certificate of safety. EPA’s Citizen’s Guide says any exposure carries some risk and that many homes can be reduced to 2 pCi/L or below. CDPHE uses that same 4 pCi/L line when it talks about mitigation in Colorado.

Start with a short-term kit if you want a first screen. CDPHE says short-term tests take about 48 to 120 hours and long-term tests take 91 days to a year under normal living. EPA says a long-term test is the better estimate of the year-round average, and a second short-term test is the right follow-up when you need a faster decision. A sale usually needs a licensed professional and a continuous monitor, which is a different path from a hardware-store charcoal kit.

CDPHE says a minimum of two days, 48 hours, after the house has already been closed for 12 hours. Many charcoal kits are designed for 48 to 120 hours. Do not pull the kit early because the weekend got busy. Write the start and stop to the minute, and do not wait more than a day to ship it to the lab named on the package.

CDPHE says the lowest inhabitable level, including an unfinished basement if that is the level you are checking, on a surface 2 to 7 feet above the floor. Choose an open, central spot in a room someone uses. Do not use a crawl space, closet, kitchen, laundry room, or bathroom. Keep it off exterior doors, windows, and walls, away from vents, fans, and direct sun, and off granite counters or a slate pool table. For a sale, CDPHE points the professional test at the lowest area that could be finished into living space.

Close exterior windows and doors 12 hours before the test and keep them closed until it ends. You may come and go. Do not leave a door standing open. CDPHE says most heating and air-conditioning systems can run as usual. Do not run a whole-house fan. A short-term test is trying to see the house the way it operates when it is shut, which is the normal winter condition for a lot of Denver homes and a condition you have to create on a mild October day.

EPA says not to run a two- or three-day test during unusually severe storms or unusually high winds. A Front Range wind event is a reason to wait, not a reason to invent a correction factor. Rain and wind can change how soil gas moves. If the weather turns extreme after you have started, note it and consider repeating the short-term test rather than treating a storm weekend as the year-round number.

That band is a maybe. EPA’s own example is an average of 4.1 pCi/L, which they say leaves about a 50 percent chance the year-round average is somewhat below 4. Do not hire a mitigator on one kit that landed on the line, and do not file the kit in a drawer. Use a continuous monitor for a few weeks in the same room, then confirm with a second short-term test or a long-term alpha-track. If the follow-up stays at or above 4.0, move to a licensed mitigator.

Radon moves with the stack effect, the heating system, wind, and whether windows were actually closed. EPA says day-to-day and season-to-season changes are expected, which is why a single short test is a weaker picture of the year than a long-term test. A kit in a guest room is also not a kit in the basement family room. Compare tests that used the same location and real closed-house conditions before you decide the lab was wrong.

Use a mail-in kit for the first screen and for a lab number you can put in a file. Use a continuous monitor when the result is near 4, when the number jumps from season to season, or when you want to see what the furnace and a closed week actually do. A monitor shows a trend. A mitigation decision still needs a follow-up test, not a glance at one afternoon’s display. The Airthings links do not insert ARS10-10OFF. After your name and shipping are in the cart, type that code for 10% off. We may earn a commission if you buy through them. American Radon Systems does not install in Denver.

CDPHE says low-cost do-it-yourself kits from home improvement stores commonly run about $10 to $50, and that you must follow the maker’s instructions or the result is not valid. Buy a kit that tells you which lab analyzes it and how to ship on time. Be wary of a listing that hides the device type or the lab. For a sale, skip the anonymous listing and hire a DORA-licensed measurement professional.

Yes, with a limit. CDPHE offers one free kit per household per year while supplies last, plus discounted kits. Order from the testing page and check whether kits are currently in stock. If the state kit is gone, CDPHE says to ask your local public health agency. In early 2025 the department said it had distributed more than 12,500 free kits. Availability changes, so the form is the source of truth, not this page.

CDPHE encourages buyers to test during the inspection period and to hire a licensed measurement professional using a professional-grade continuous monitor or another approved device. The test location for a sale is the lowest area that could become living space. If the result is elevated, the buyer and seller negotiate the system. This guide is not a substitute for the contract or for a lawyer. Read CDPHE’s real-estate notes on the testing page and EPA’s home-buyer materials linked from the publications list.

Confirm the system with a short-term test after it is running, then retest on a schedule. CDPHE has told Colorado homeowners who already have a system to retest about every two years. Also retest after you finish a basement, add an addition, or change the heating system or the tightness of the house. A fan that is unplugged is not a mitigation system.

No. CDPHE says sealing is part of a mitigation job so conditioned air stays in the house, not a way to keep radon out by itself. It is impossible to find every crack, and sealant ages. EPA’s Consumer’s Guide says the same: sealing alone is not recommended. The reliable method is usually a soil-suction system under the slab or a membrane in a crawl space.

Someone licensed by the Colorado Department of Regulatory Agencies as a radon mitigation professional. CDPHE notes that listed contractors are certified by NRPP or NRSB and must hold the state license. Look them up on the DORA radon page or the license lookup. You can also search NRPP and NRSB. This guide does not recommend a company, and American Radon Systems does not install in Denver.

CDPHE says tenants may test their own units. As of August 7, 2023, Colorado landlords must disclose radon information when a tenant signs a lease, under SB23-206. Read the rental section of the CDPHE testing page and EPA’s tenant guide. A tenant test tells you about the unit. A building-wide fan is the owner’s decision. This page is not legal advice.

Test the air first. CDPHE says if your water is from a private well and the air test found a radon problem, test the water too. EPA’s Citizen’s Guide makes the same order: air first, then water if the supply is a private well and indoor air is high. A public water system is a question for the supplier, not a reason to skip the air test in the house.

CDPHE says all homes should be tested, including apartments. A ground-floor unit and a unit over a crawl space or a garage are the usual places to start, because soil gas enters low. Upper floors can still be tested. In a shared building, a mitigation system may need the association or the owner. Test the unit you occupy, and do not assume the unit across the hall has the same result.

Yes. EPA says every new home should be tested after people move in, even when radon-resistant features were built in. A passive vent without a fan is not a promise that the level is under 4. This guide does not claim a Denver building-code section it has not cited. If a builder says the house is radon-ready, ask what was installed, then test the finished house anyway. Colorado does require schools and child-care facilities to test and keep records, which is a different rule from single-family construction.

No. Radon has no odor, and a pet is not a detector. EPA’s reduction method is a soil-suction system, not a plant. Houseplants are not listed by EPA or CDPHE as a way to bring a house under 4.0 pCi/L. If you share the house with animals, that is another reason to know the number, not a way to measure it.

EPA says the risks combine: people who smoke and live with a higher radon level have an especially high lung-cancer risk. CDPHE’s health page says to avoid smoking or vaping indoors and to consider quitting. Fixing the house does not replace quitting, and quitting does not replace a test. The EPA risk page and the Citizen’s Guide are the national sources. This guide is not medical advice.

EPA says to test again if you start using a lower level of the house, such as finishing a basement, and CDPHE points people with a mitigation system toward a retest about every two years. A low first result is not a lifetime pass. Retest after renovations that tighten the house or change the heating system. Save the lab report so a future buyer is not starting from zero.

Use a DIY kit for your own information when you can follow closed-house rules and ship on time. Hire a licensed professional, around the figure CDPHE mentions of about $150, when the result has to hold up in a sale or when you want a third party to run the test. CDPHE’s FAQ makes that distinction. The license lookup is at DORA, not a list printed on this site.

These are published ranges, not a bid. CDPHE says do-it-yourself kits at home improvement stores run about $10 to $50, a licensed measurement is around $150, and a mitigation system in Colorado usually costs about $1,000 to $2,000 unless the design is difficult. The state also points to a low-income mitigation assistance program in its January 5, 2026 release. Get itemized bids from licensed contractors. This guide does not set prices.

CDPHE says it is always a good time if you can keep the house closed, and that some people find that easier in winter. EPA also says to avoid unusually severe storms and high winds for a two- or three-day test. A still, closed week in January is a fair short-term screen. A windy chinook day is a reason to wait. A long-term test that includes both heating and milder months is the better year-round picture if you are not in a hurry.

Yes, the room changes, the action level does not. A basement that people use is the usual test spot. A slab-on-grade house is tested in the lowest lived-in room, still 2 to 7 feet off the floor under CDPHE’s placement rules. Do not hang a homeowner kit in the crawl space itself. If a crawl space is the pathway, a mitigator looks at sub-membrane depressurization, which CDPHE describes on the testing page. The kit still belongs in living space.

Ask before the fan is ordered. A typical system exhausts above the roof, so the association may have a rule about penetrations, color, or where a pipe may show. That is a design conversation with the association and the licensed contractor, not a radon measurement. This guide does not claim a Denver ordinance about HOA pipes. Bring the association’s written rules to the bid so the contractor prices the route that is actually allowed.

Give them the lab report or the professional’s report, the dates, the device type, and where the test sat. Say whether the house was under closed conditions. If a system is installed, include the permit or invoice you have and the latest retest. EPA notes that a fixed house is often easier to sell than an unknown house. Do not summarize a 3.8 and a 6.2 as “we’re fine.” Hand over both pages. The realtor notes on this site are the longer version.