If you've searched "active soil depressurization," "active sub-slab depressurization," or "active subslab suction" and gotten three different explanations, you're not alone — they're all the same system with different names. Below is a plain-language breakdown of how it works, what it costs to run, and what counts as an acceptable radon level if you're testing a home in Arvada, CO or elsewhere along the Front Range.
What is an active soil depressurization system?
An active soil depressurization (ASD) system is a radon reduction method that uses a fan-powered vent pipe to pull radon gas from beneath a home's foundation and exhaust it above the roofline before it can enter living space. It's the system the U.S. Environmental Protection Agency (EPA) identifies as the most common and effective radon fix for existing homes.
The word "active" distinguishes it from a passive system, which relies only on natural air pressure differences and lacks a fan. Nearly every radon system installed by the licensed operators in our network in Colorado today is active, because passive systems alone rarely pull radon levels below the EPA's action guideline.
How does active sub-slab depressurization work in a Colorado home?
Active sub-slab depressurization works by drilling one or more suction points through the basement or slab floor, inserting PVC pipe into the soil or gravel beneath it, and running that pipe through a continuously operating in-line fan to the exterior, where it vents above the roof edge. The fan creates negative pressure under the slab that intercepts radon before it seeps indoors.
- Suction point: Usually a 4- to 6-inch hole through the slab, sealed airtight around the pipe once installed.
- Fan placement: Typically mounted in an attic, garage, or exterior wall — never inside a living space, per manufacturer and code guidance, so any leak vents outdoors, not indoors.
- Manometer: A small U-tube gauge installed near the pipe shows at a glance whether the fan is running, so a homeowner can do a 5-second visual check anytime.
In homes with multiple foundation types — a common situation in older Jefferson County and Denver neighborhoods where additions were built over crawlspaces or slab extensions — more than one suction point or a secondary fan may be needed to depressurize the whole footprint evenly.
What's the difference between active subslab suction and a passive radon system?
Active subslab suction uses an electric in-line fan running 24/7 to continuously depressurize the soil under a foundation, while a passive system relies only on natural stack effect and has no fan. Passive systems are sometimes built into new construction but are rarely sufficient on their own to bring an existing home's radon level down reliably.
Because Colorado's Front Range sits on soils and geology known for elevated radon potential, most retrofit installations here start as active systems from day one rather than being upgraded later from passive.
What is an acceptable radon level in Colorado?
The EPA recommends taking action to reduce radon when a home's average level is 4 picocuries per liter (pCi/L) or higher, and considers 2–4 pCi/L worth reducing when practical. Colorado does not set a separate state action level — homes here are measured against the same EPA guideline used nationwide.
Radon levels can vary significantly between rooms, floors, and seasons, so a single short-term test result should be treated as a screening tool, not a final verdict. For a deeper look at typical readings by area, see our guide to average radon levels in Arvada and Boulder.
Why do radon levels change with the seasons in Colorado?
Radon levels in Colorado homes often rise in winter because closed windows, running furnaces, and stronger indoor-outdoor pressure differences (the "stack effect") pull more soil gas into the house. Short-term tests done in winter tend to read higher than the same home tested in mild spring or fall weather.
This is one reason the EPA recommends closed-house conditions during testing regardless of season — windows and exterior doors kept shut except for normal entry and exit — so results are comparable no matter when a test is run.
How do I get a radon test done in Arvada, CO?
A radon test in Arvada, CO typically involves placing a short-term test device (charcoal canister or continuous monitor) in the lowest livable level of the home for 48 hours under closed-house conditions, then reading or lab-analyzing the result. Homeowners can buy a DIY kit or have a professional place a continuous monitor for a more tamper-resistant reading, especially during a real estate transaction.
Colorado does not currently license radon measurement or mitigation professionals through a state board, but the Colorado Department of Public Health & Environment (CDPHE) directs residents to hire contractors certified through the National Radon Proficiency Program (NRPP) or National Radon Safety Board (NRSB) — the same national certifying bodies the licensed operators in our network hold credentials through.
What does an active soil depressurization system cost to install and maintain?
Installation cost for an ASD system varies by home size, foundation type, and number of suction points needed, so get a written, itemized quote after an in-person or photo-based evaluation rather than relying on a phone estimate. Ongoing cost is mainly electricity for the fan, which runs continuously, plus occasional fan replacement — most in-line radon fans are rated for roughly 5-10 years of continuous use before needing replacement.
A functioning system should show steady negative pressure on its manometer at every check; a reading that flattens out or reverses is the clearest sign the fan has failed and the system needs service.
This article is educational and does not replace a site-specific radon test, an in-person system evaluation, or guidance from the Colorado Department of Public Health & Environment. Radon test results and mitigation needs vary by property; always confirm current requirements with your municipality and a certified radon professional before making a testing or mitigation decision.