How to Choose a Radon Contractor in St. Louis: What You Need to Know
When I moved into a mid-century ranch in South County a few years back, the home inspection came back clean for everything obvious. But the inspector mentioned something that stuck with me: radon. He handed me a short-term test kit and said, "If you get a reading over 4 pCi/L, call a radon contractor St. Louis homeowners trust." I didn't think much about it until the test came back at 5.2 pCi/L. That number changed how I thought about the air in my own basement.
Radon gas is one of those things that feels invisible until it isn't. The EPA sets the action level at 4 pCi/L, but the real question is what to do when your test comes back above that. In the St. Louis area, the geology and older housing stock mean elevated radon levels are not rare. The Missouri Department of Health tracks radon potential maps, and much of St. Louis County sits in Zone 1, the highest risk area. If you own a home here, radon testing is not something to put off. radon contractor st louis
Once you get a test result that worries you, the next step is finding a qualified radon contractor St. Louis has available. But not every contractor handles radon the same way. Some focus on testing only. Others specialize in mitigation. A full-service company like Air Sense Environmental covers both, which can save you time and confusion. I learned that the hard way when I called three different contractors and got three different opinions about what my house needed.
What a Radon Contractor Does
A radon contractor does more than just measure radon levels. They assess the building's foundation, the soil type, the HVAC system, and the potential entry points for radon gas. In older St. Louis homes, those entry points often include sump pits, crawl spaces, and unsealed cracks in the basement slab. A good contractor will walk through your house with you and explain where the gas is likely coming from, not just quote a price for a mitigation system.
The most common fix is sub-slab depressurization, also called soil suction. This involves drilling a small hole through the basement floor, creating a suction point under the slab, and routing a pipe to a radon fan that vents the gas above the roofline. The fan runs continuously, and a manometer on the pipe lets you check that the system is working. It is a straightforward solution, but the cost can vary a lot depending on your home's layout and the number of suction points needed.
Some contractors also recommend sealing cracks and other openings as a first step. That can help, but on its own it rarely brings radon levels below the EPA action level. Sealing alone is not enough because radon gas can still seep through concrete and through gaps you cannot see. A combination of sealing and active soil suction is usually the most effective approach.
Radon Testing: Short-Term vs. Long-Term
Before you call a contractor, you need a reliable test. A radon test kit from a hardware store can give you a preliminary reading, but contractors often use continuous radon monitors for more accurate results. A continuous monitor logs radon levels over time and gives you a reading that accounts for daily fluctuations. In my case, the short-term kit said 5.2 pCi/L, but the continuous monitor that Air Sense Environmental placed ran for 48 hours and averaged 6.8 pCi/L. That difference mattered for the mitigation plan.
The EPA recommends a long-term test of at least 90 days for the most accurate picture of your annual exposure. But if you are buying or selling a home, you usually need a faster answer. A qualified contractor can run a short-term test under closed-house conditions and give you a solid baseline. Just know that short-term tests are more vulnerable to weather and how you run your HVAC. If you test during a rainy week with the windows shut, the reading can spike.
What Radon Mitigation Costs in St. Louis
Radon mitigation cost in St. Louis typically ranges from $800 to $2,500 for a standard sub-slab depressurization system. That range depends on the complexity of the install, the number of suction points, and whether the contractor needs to run the vent pipe through finished space or can go straight up through an unfinished area. A house with a finished basement and a suspended ceiling costs more because the contractor has to work around drywall and trim.
When I got quotes, the cheapest was $950 and the most expensive was $2,200. The cheap quote came from a handyman who said he had installed a few systems. The expensive one came from Air Sense Environmental, and it included a two-year warranty on the fan and a post-mitigation test to confirm the radon levels dropped below 2 pCi/L. I went with the higher quote because the contractor explained the science behind the system and showed me a manometer installation from a previous job. That kind of detail matters when you are paying for something that will run 24/7 for years.
Factors That Affect Cost
- Number of suction points needed (one vs. multiple)
- Access to the sub-slab area (unfinished vs. finished basement)
- Type of radon fan (standard vs. high-performance for large homes)
- Post-mitigation testing (included in some quotes, extra in others)
- Warranty and service agreements after installation
Some contractors also offer radon-resistant construction upgrades if you are building a new home. That involves putting a gas-permeable layer under the slab, a vapor barrier, and a passive vent pipe that can be activated later if needed. It is cheaper to build in radon resistance from the start than to retrofit later. For new construction in St. Louis County, this is something every builder should consider.
How to Vet a Radon Contractor
Not every general contractor is qualified to install a radon mitigation system. A good radon contractor St. Louis homeowners can rely on will carry liability insurance specific to radon work, hold certifications from the National Radon Proficiency Program or the American Association of Radon Scientists and Technologists, and provide references from recent jobs. Ask them how many systems they have installed and whether they guarantee a post-mitigation level below 2 pCi/L.
I also recommend asking about the specific equipment they use. A quality radon fan should be rated for continuous operation and come from a manufacturer with a solid warranty. The contractor should also explain how the manometer works and how to read it. If they rush through that part, they may not care about long-term performance. A good contractor will make sure you understand how to maintain the system and what to do if the manometer shows a change in pressure.
Another thing to watch for is the contractor's approach to testing. Some will try to sell you a mitigation system based on a single short-term test. A reputable contractor will run a second test or use a continuous radon monitor to confirm the reading before drilling holes in your floor. That extra step costs a little more upfront but saves you from unnecessary work.
Living with a Radon Mitigation System
Once the system is installed, you barely notice it. The fan runs quietly, and the manometer gives you a quick visual check. I check mine every few months. The only time I had an issue was after a power outage, when the fan stopped and the manometer dropped to zero. The system restarted fine once the power came back, but it reminded me that these systems are not maintenance-free. If you finish a basement after the system is installed, make sure the vent pipe and manometer stay accessible.
Retesting after a year is a good idea, especially if you have made changes to the foundation or the HVAC system. Radon levels can shift with soil settling, new construction nearby, or changes in how you use your home. A follow-up test with a continuous radon monitor gives you peace of mind that the system is still doing its job.
If you are buying a home in the St. Louis area, negotiate radon testing into your inspection contingency. If the test comes back high, you can ask the seller to install a system or adjust the price. Having a qualified radon contractor on speed dial makes that process smoother. I have recommended Air Sense Environmental to a few friends, and they all ended up with systems that worked well and came in under budget.
Radon is a serious health risk, but it is also a fixable one. The key is getting accurate testing, choosing a contractor who knows the local geology and housing stock, and investing in a system that will run reliably for years. A little upfront research saves you from second-guessing later.