When a Huntsville home tests at or above the EPA's 4 pCi/L action level, the fix is almost always a radon mitigation system: a sealed pipe, a fan, and some careful sealing that together lower the air pressure under the house so soil gas goes up the pipe instead of into your living room. This page explains how those systems work, what a good installation looks like, what affects the price, and what to ask before you hire someone.
How active soil depressurization works
Houses tend to sit at slightly lower air pressure than the soil beneath them. Warm air rising inside, exhaust fans, and dryers all create a gentle suction that pulls soil air through any gap in the foundation. A mitigation system reverses that. A fan creates stronger suction in the soil than the house does, so radon follows the pipe and is released outdoors, above the roofline, where it quickly dilutes.
The EPA's term for this family of methods is active soil depressurization, and it is the most widely used approach for existing homes. The specific design depends on what's under the floor:
- Sub-slab depressurization for basements and slab-on-grade homes. A suction hole goes through the slab and a pipe connects it to the fan. See sub-slab depressurization.
- Sub-membrane depressurization for crawl spaces. A heavy plastic barrier is sealed over the dirt floor and the system draws from beneath it. See crawl space mitigation.
- Drain tile or sump suction, where a house already has perimeter drains or a sump pit that can serve as the suction point.
- Block-wall depressurization, for hollow concrete-block foundation walls that act like chimneys for soil gas.
Many Madison County homes combine two of these. An older house with a basement under the original structure and a crawl space under a later addition may need a system that draws from both.
The parts of a typical system
- Suction point. A hole through the slab, usually with a small pit dug out beneath it so the fan can reach a wider area.
- PVC vent pipe. Schedule 40 pipe runs from the suction point to the fan and then to a discharge point. Pipes can run inside, through a closet or garage, or outside along an exterior wall.
- Inline radon fan. Mounted in the attic, garage, or outside, never in the living space or basement, because the pipe after the fan is under positive pressure.
- Discharge above the roof. The exhaust should vent above the roof edge and away from windows and doors so the gas doesn't re-enter the house.
- Manometer. A U-tube gauge on the pipe that shows the system is pulling suction. If the liquid levels even out, the fan has stopped.
- Sealing. Caulk or foam at accessible cracks, the sump lid, and floor-wall joints so the system pulls from soil, not from your basement air.
What good work looks like
Industry standards, specifically the ANSI/AARST soil gas mitigation standards used by certified mitigators, cover pipe slope, fan location, labeling, electrical work, and discharge placement. A careful installer will:
- Do a diagnostic before quoting, often a vacuum test at a test hole to see how air moves under your slab.
- Label the pipe and leave you instructions on reading the manometer.
- Seal around the pipe where it passes through the slab and walls.
- Route pipe neatly, with attention to appearance on the outside of the house if it runs up an exterior wall.
- Recommend a post-mitigation test no sooner than 24 hours after the system starts and within the first 30 days.
Since Alabama doesn't license radon contractors, ask if the installer holds NRPP or NRSB mitigation certification. Those national programs require training, an exam, and continuing education.
What mitigation costs
Prices vary from house to house. Angi's 2026 data, based on 1,184 projects, puts the typical national cost of an active suction system at about $805 to $1,326, with an average around $1,043. Larger homes, multiple suction points, crawl spaces that need a full membrane, and long interior pipe routes can push a job higher. Permits, where required, are usually a small addition.
These are typical national ranges, not Huntsville prices. We don't set prices, and every professional we connect you with quotes their own work after seeing the house.
What changes the price
- Foundation type. Plain slabs are usually simplest; crawl spaces add membrane material and labor.
- Sub-slab material. Clean gravel under a slab lets one suction point cover a large area. Dense clay, which is common in north Alabama soils, may need more suction points or a stronger fan.
- Pipe routing. An interior route through a closet into the attic costs more labor but looks cleaner; an exterior route is often faster.
- Electrical. The fan needs a dedicated outdoor-rated circuit or an existing one nearby.
- Finished basements. Carpet, built-ins, and drywall limit access to the slab.
Running costs and maintenance
A radon fan runs around the clock. Most residential fans draw a modest amount of power, so electricity is usually a small monthly cost. The bigger factor in Huntsville can be conditioned air: in some houses the system draws a little indoor air into the soil, which can slightly increase heating and cooling loads. Ask the installer about it.
Fans typically last many years but don't last forever. Check the manometer every few months. If it reads zero or the fan is silent, call for service. Retest the house every two years or so, and again after any big renovation.
Will it get my level below 4 pCi/L?
In most homes, a well-designed active system brings radon well below the action level, and many installers guarantee a result below 4 pCi/L. Get that guarantee in writing, along with the fan warranty and what happens if the post-mitigation test is high.
Questions to ask before you hire
- Are you NRPP or NRSB certified for mitigation, and can I verify it?
- Will you do a diagnostic before quoting?
- Where will the fan and pipe go, and can I see a sketch?
- What reduction do you guarantee, and what happens if the retest is high?
- What's the fan warranty, and who services the system?
- Who handles the post-mitigation test, and is it independent of the installer?