What Happens During a Radon Mitigation Installation? A Step-by-Step Guide
Your home tested high for radon. Now what?
If you have read our guide on why radon matters in Missouri homes, you already know the short answer: mitigate it. The EPA action level is 4.0 pCi/L, and Missouri has one of the highest rates of elevated-radon homes in the country, especially across Saint Francois County, Jefferson County, and parts of the St. Louis metro.
Learn more about professional radon mitigation before you hire — certification and system design matter as much as price.
But most homeowners have never watched a radon mitigation system get installed and don't know what they're actually buying. This walkthrough covers what happens, start to finish, so you can go in with realistic expectations.
How Radon Mitigation Works (Quick Primer)
Radon is a radioactive gas that seeps up from soil into homes through foundation cracks, sump openings, crawlspaces, and utility penetrations. Once inside, it gets trapped and concentrates.
The most effective and widely-used mitigation method for Missouri homes is Active Soil Depressurization (ASD). The idea is simple: install a continuously-running fan that pulls air from under the home and vents it safely outside, creating slight negative pressure beneath the slab or in the crawlspace. Radon follows the suction out instead of rising into the house.
When installed correctly by a certified mitigation contractor, an ASD system typically reduces indoor radon by 85-95%.
Here's how the installation goes.
Step 1: Site Assessment
Before any work starts, a certified mitigation specialist visits the home to assess:
- Foundation type (slab, basement, crawlspace, or a mix)
- Sub-slab conditions (gravel bed, soil type, existing drainage)
- Existing sump pumps or radon pathways
- Ideal suction point (usually in the basement or under a slab, out of the way)
- Best venting path (up through the home to the roof, or along the exterior wall)
- HVAC system (to make sure the mitigation fan doesn't create pressure issues)
This walkthrough usually takes 30-45 minutes. The contractor will explain where pipes will run, where the fan will mount, and what the finished system will look like.
Step 2: System Design
Based on the assessment, the contractor designs a custom system:
- Suction point location (often through the basement slab or into the crawlspace vapor barrier)
- Pipe routing (interior up through a closet or garage, or exterior along the side of the home)
- Fan placement (typically mounted outside above the roofline, or in an attic or garage)
- Manometer placement (a small U-tube gauge visible to the homeowner that confirms the system is running)
A good contractor will walk you through the design before installation day so there are no surprises.
Step 3: Installation Day
Most single-family Missouri homes take 4 to 8 hours for a standard mitigation installation. Here's the typical sequence:
- Core-drill the suction point. A 4- to 6-inch hole is cut through the basement slab or sealed into the crawlspace vapor barrier.
- Install the sub-slab pipe. 3- or 4-inch PVC pipe is sealed into the suction hole with specialized sealant.
- Route the pipe upward. Pipe is run through the home (enclosed in closets or chases) or along the exterior wall, up to the fan location.
- Mount the radon fan. The fan is installed outside above the roofline (most common) or in an attic or garage. Fans are sealed, UL-listed, and designed for continuous operation.
- Install the exhaust. Exhaust pipe extends above the roof eave to vent radon safely away from windows and people.
- Install the U-tube manometer. This gauge lets you verify the system is running just by looking at it.
- Seal foundation cracks and openings. Any visible crack or penetration in the slab or crawlspace gets sealed to improve system efficiency.
- Test system operation. The fan is turned on, suction is verified, and the manometer is checked.
Most installations are finished the same day. There's some drilling noise and some dust, but it's not a teardown.
Step 4: Post-Installation Testing
After the fan runs for at least 24 hours, a follow-up radon test confirms the system is working. You'll get the new reading — for most Missouri homes, the post-mitigation number drops to below 2.0 pCi/L, often below 1.0.
If the first test doesn't hit target, a certified contractor will make adjustments (sealing additional cracks, adjusting fan size, adding a secondary suction point) at no additional cost under a standard workmanship warranty.
Step 5: Long-Term Follow-Up
A radon mitigation system is low-maintenance but not zero-maintenance:
- Retest every 2 years (or after any major home renovation) to confirm the system is still effective
- Check the manometer monthly. Both sides of the U-tube should read at different levels. If they read the same, the fan has failed and needs service.
- Replace the fan every 10-15 years. They run continuously, so they eventually wear out.
What It Costs
For a typical Missouri single-family home, expect:
- $1,000 to $1,500 for a basic basement installation with a standard fan
- $1,500 to $2,000 for homes needing longer pipe runs, exterior routing, or larger fans
- $2,000 to $2,500+ for crawlspace systems, split foundations, or homes needing multiple suction points
Most jobs land in the $1,200-$1,800 range.
What It Looks Like When It's Done
The only visible pieces are:
- A white 3- or 4-inch PVC pipe running up through a closet, garage, or along the exterior
- A small box-shaped fan (about the size of a shoebox) mounted outside above the roofline or in the attic
- A small U-tube manometer mounted somewhere visible, usually in the basement or utility room
Interior-routed systems are nearly invisible once the closet door is closed. Exterior-routed systems look like a standard plumbing stack.
Why Certification Matters
Radon mitigation in Missouri is regulated. Installation must be done by a contractor certified through either the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB). Uncertified installations may not meet EPA standards and won't hold up under inspection.
Always ask for certification credentials. Any legitimate contractor will provide them without hesitation.
When to Call Eagle Air
Eagle Air provides certified radon mitigation services across Saint Francois County, Jefferson County, Madison County, Washington County, and the greater St. Louis area. Every installation starts with a free site assessment, includes post-install retesting, and comes with a workmanship warranty. If your test came back high, the next step is the easiest part of the whole process — scheduling that first visit.