--- title: Passive vs. Active Radon Systems canonical: "https://radonmitigationyorkpa.net/radon-guide/passive-vs-active-radon-system/" pubDate: "2026-10-01T00:00:00.000Z" updatedDate: "2026-10-03T00:18:00.000Z" author: Radon Mitigation York PA description: "Passive radon systems rely on natural draft; active ones use a fan. Compare how well each works, costs, upkeep, and when to switch." --- # Passive vs. Active Radon Systems The difference between a passive vs. active radon system is the fan. A passive system is a pipe from under the slab to the roof that relies on natural draft. An active system adds a fan that creates steady suction under the slab, and [adding a fan to a passive system](/services/passive-radon-system-activation/) turns one into the other. EPA says passive suction is generally less effective, and many passive homes still test above 4.0 pCi/L. ## How each system works Both systems start with the same idea: give soil gas under your basement floor an easier path out of the house than through cracks and openings. **Passive system.** A PVC pipe runs from the gravel under your slab, through the house, and out the roof. Warm air rising in the pipe creates a weak draft. That draft pulls some soil gas up and out. **Active system.** The same kind of pipe, plus an in-line fan located in the attic or outside. The fan creates lower pressure under the slab than inside the house, so soil gas flows into the pipe instead of into your home. EPA calls this active sub-slab suction, also known as sub-slab depressurization. ## Side-by-side comparison | Feature | Passive system | Active system | |---|---|---| | Fan | None | In-line fan in attic or outside | | How it moves soil gas | Natural draft (stack effect) | Steady fan suction | | Effect of weather | Large: weaker in mild weather | Small: suction stays steady | | Warning device | Usually none | Manometer and often an alarm | | Electricity | None | About as much as a light bulb or two | | Moving parts to replace | None | Fan, every several years | | Typical use | New construction, low radon | Homes testing at 4.0 pCi/L or higher | ## Does a passive system work without a fan? Sometimes, partially. A passive stack can lower radon in some homes, especially in cold weather when the draft is strongest. But EPA's [Consumer's Guide to Radon Reduction](https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf) states that passive sub-slab suction is "generally not as effective in reducing high radon levels as active subslab suction." Many homes with passive systems still test at or above the EPA action level of 4.0 pCi/L. That is the reason passive systems are designed so a fan can be added. EPA's guidance for new home buyers says that if you test at 4 pCi/L or more, "a vent fan can easily be added to the passive system to make it an active system and further reduce radon levels." The only way to know how your passive system performs is to test. ## Pros and cons ### Passive **Pros** - No electricity or noise. - No fan to wear out. - Lower cost when built in during construction. **Cons** - Weak and changes with the weather. - No built-in way to see if it is working. - Often not enough in high-radon homes. ### Active **Pros** - Steady suction all year. - A gauge and alarm show that it is working. - Can be tuned with a larger fan or extra suction points. **Cons** - Uses a small amount of electricity. - The fan will need replacing at some point. EPA notes fans may last five years or more. - Makes a low hum near the fan. ## When to switch from passive to active Add a fan if: - Your radon test is 4.0 pCi/L or higher. - Your test is between 2 and 4 pCi/L and you want it lower. EPA says to consider fixing at this level. - You are finishing the basement or will spend more time on the lowest level. - You are selling and the buyer's test came back high. Before activation, confirm what you actually have. The pipe should run from below the slab all the way out the roof. Our guide on [how to tell if your house has a radon pipe](/radon-guide/how-to-tell-if-house-has-radon-pipe/) shows what to look for. ## What activation looks like Activating a passive system usually means: 1. Adding a fan in the attic or outside, never in living space. 2. Running power to the fan on a circuit with no wall switch. 3. Adding a manometer and often an alarm. 4. Sealing accessible cracks and the sump lid. 5. Running a clearance test no sooner than 24 hours after the fan starts and within 30 days. ## Passive vs. active in York York County is in EPA Radon Zone 1, the highest-potential group. See the [EPA map of radon zones](https://www.epa.gov/radon/epa-map-radon-zones-and-supplemental-information). In a high-radon area, a passive stack's weak draft is often not enough. Pennsylvania's statewide code does not require radon-resistant construction, so whether a newer York home has a passive pipe depends on the builder. ## Key takeaways - The difference is the fan: passive uses natural draft, active uses a fan. - EPA says passive suction is generally less effective than active suction. - Many passive homes still test at or above 4.0 pCi/L. - A fan can usually be added to a passive stack. - Test to know which one your home needs. ## Frequently Asked Questions ### Is an active system noisy? A well-installed fan makes a low hum near the fan and is barely heard indoors. The fan sits in the attic or outside. ### Can a passive system be enough? If your home tests low, below 2 pCi/L, and stays there on retests, a passive stack may be all you need. Keep retesting every two years. ### Does activation require a new pipe? Usually not. The existing stack is used if it is intact and properly routed. ## Ready to add a fan? If your passive system isn't keeping radon low, we can activate it. Call [(717) 356-3035](tel:+17173563035) any time for a same-day callback.