Radon Testing in Colorado Homes: A How-To

Radon is a colorless, odorless radioactive gas that comes from the breakdown of uranium in soil. It moves up through the ground and can collect in homes, especially in basements and lower levels. The Colorado Department of Public Health and Environment (CDPHE) says high radon levels have been found in all 50 states and in all parts of Colorado, and that about half the homes in Colorado have radon levels higher than the EPA's recommended action level of 4 picocuries per liter (pCi/L).

That's why a radon test is one of the cheapest and most useful things a Front Range homeowner can do.

Why your neighbor's result doesn't tell you yours

Radon levels vary from house to house, even on the same street, because they depend on the soil under the house, cracks and openings in the foundation, and how air moves through the building. The only way to know your level is to test your own home.

How to test

Short-term tests run from a couple of days to a few days. They're inexpensive and give a quick reading. Results can vary with weather and season.

Long-term tests run for months and give a better picture of your average exposure.

For a test to be meaningful:

1. Place it in the lowest level you use or plan to use, such as a basement family room or bedroom.
2. Keep it away from drafts, exterior walls, sump pits, kitchens and bathrooms.
3. For short-term tests, keep windows and exterior doors closed except for normal entry and exit, following the kit's instructions.
4. Mail it to the lab promptly, if it's a lab kit.

Many people run a short-term test first. If the result is at or above 4 pCi/L, follow up with a second test or a long-term test before deciding on mitigation.

When to test

• Before finishing a basement. It's far easier to install a mitigation system before the walls go up. See finishing a basement in Denver.
• When buying a home. Radon testing is a common part of inspections.
• After mitigation, to confirm it worked.
• After major renovations, such as additions, foundation work or HVAC changes, which can change air pressure and pathways.
• Every few years otherwise, since conditions can change.

What mitigation involves

The most common system is active soil depressurization: a pipe through the slab, a fan that pulls soil gas from under the house, and a vent that discharges it above the roof. Contractors also seal cracks and openings. HomeGuide's radon guide (updated February 5, 2026) says an active soil depressurization system costs $1,200 to $2,000 installed on average, and can cost more for larger homes.

Denver's residential permitting checklist for new homes and additions includes radon mitigation details: the vent pipe location, a pipe that extends up through the building and terminates above the roof, and that it may not be located in an exterior wall. Many metro cities require a permit for a radon system. Parker, for example, lists radon among the projects that need permits.

Choosing a mitigation contractor

• Ask how they'll route the pipe, where the fan goes and where the exhaust terminates.
• Ask whether a permit is required in your city and who pulls it.
• Ask whether they'll do a post-mitigation test, or whether you should hire an independent tester.
• Get a written description of the system, including fan model and warranty.
• If they're adding an outlet or circuit for the fan, it needs a licensed electrician.

Living with a system

Mitigation fans run continuously. Most systems have a gauge (a U-tube manometer) showing that the fan is pulling air. Check it occasionally and retest every few years. If the fan stops, call the installer.

For basement projects, see our basement finishing guide. Local notes for Denver and Boulder are on the area pages.