Do you have interior drains in your home? What about window-well drains? “Daylight” ends? Does water drain into any open sump pits? Does your crawlspace collect water?
Water is a huge consideration for radon system design. It’s a huge consideration for home design and construction. When you combine a home that wasn’t designed for radon, but was designed for water, well now you have some work to do if you want things to function properly and efficiently.
Sub-soil depressurization is the technical term for an efficient radon system. This means you only remove soil air. You can get your radon levels down by removing more than just the soil air. That’s why unscrupulous contractors will open windows or increase air exchanges to pass a radon test (often ineffectively). However, long term exhaust of conditioned, indoor air is an extremely costly way to tackle your radon problem*.
Here’s where check valves come in. A check valve—or one-way valve—is a product that is designed to let water flow in one direction, but stop air from flowing in another direction. Here are some examples:
#1. A traditional suction pit system is not working properly after being installed by an apprentice tech. The radon mitigation professional makes a site visit and finds out that there are window well drains and floor drains in the home that are short-circuiting the pressure field. The radon fan is grabbing air from those drains and no further. Check valves are installed and voila, the radon levels and the HVAC bill both plummet. 
#2. A radon mitigation system is installed over a crawl space. The contractor and homeowner both forget to discuss water drainage. Heavy rains flood into the crawl space regularly and standing water forms on top of the radon vapor barrier. A check valve is installed in the barrier and the water is allowed to drain down into the soil as it had for decades before. The homeowner is now protected from moist air from untreated water and all the dangers that can come with it.
#3. A suction pit radon system is installed by an untrained, uncertified professional. Due to their lack of education, they don’t notice that there is an existing sump well with drainage throughout the home. The radon levels are later monitored by the homeowner and found to be unacceptably high at certain times of year. A qualified, trained radon professional makes a site visit and finds an unsealed sump and many unsealed floor drains. The sump was left open because water drains into it from the floor during heavy rains. No problem for the real professional. One-way valves are installed on all floor drains and the sealed sump lid itself. The radon levels and the HVAC bill both plummet.
#4. A radon pro ties into a buried french drain system without ever having to penetrate the exterior of the home: an elegant solution pioneered by early Colorado Springs pros. This is sometimes called a “dig-down” system, as the pro often can dig down next to a window well and find the drain-tile loop, then tie into it with a french connection–one of its many uses. They install check valves in all the window well drains, but in their haste to finish before a real estate transaction, they fail to notice that there is a “daylight” drain at the edge of the property. It drains off a hill via gravity (and it happens to have a dead snake in it). This daylight has short-circuited the PFE and the radon levels remain high. The contractor returns to the site and installs at Alpha86 drain check valve. Critters are now locked out of this drain and the PFE for the system is complete. Radon levels are reduced dramatically.
*As you can see, ensuring your radon system is only evacuating soil air can solve a multitude of problems. An educator at a world-renowned radon trade school once calculated that the air loss from a standard radon fan and a mere 25’ of unsealed floor cracks added up to over $1,200 in additional HVAC bills over the life of that radon fan. Improper system design hits you in the wallet, not just the lungs.
Pro Search Tip, use these terms on our search bar above: volcano drain, EZ flow, drain check, or Dranjer
Thanks for reading!
