Active vs. Passive Radon Mitigation Systems
If you are buying new construction or upgrading a home in EPA Zone 1, you might hear the term "passive radon system." But what actually makes a system active vs passive, and why does one cost so much more to run?
The Passive Radon System (RRNC)
A "passive system," more accurately known as Radon-Resistant New Construction (RRNC), is a PVC vent pipe routed naturally from beneath your basement floor slab directly up through the walls and out of your roof.
How it works: Passive systems rely entirely on the "stack effect." Warm air naturally rises up through the home, theoretically carrying the radon gas up through the pipe from the gravel pit below and safely discharging it above the roofline.
Does a passive system work?
Sometimes. If soil permeability is high and the natural draft is strong, it can reduce levels by up to 50%. However, the EPA strongly advises that passive systems frequently fail to drop levels below 4.0 pCi/L in highly concentrated areas, particularly during the winter when house stack drafts alter.
The Active Radon System (ASD)
An "active system," known as Active Sub-Slab Depressurization (ASD), takes the exact same PVC pipe network but aggressively powers it with an inline radon mitigation fan (typically mounted in the attic or exterior).
How it works: The fan creates a permanent negative pressure vacuum under the concrete slab. Instead of relying on a weak natural draft, the fan aggressively sucks the radon out of the dirt and blasts it out the roof. Active systems are highly reliable and regularly reduce toxic indoor air levels by 80–99%, pulling readings down to 1.5 pCi/L or lower.
Can you upgrade passive to active?
Yes! The brilliance of modern new construction building codes is the "Activating a Passive System" process. If you test your new home and the passive pipe isn't cutting it, a certified mitigator simply cuts a section of the existing PVC in the attic, glues in a $200 radon fan, wires it to a junction box, and places a u-tube manometer in your basement. Boom—your system is now active for a few hundred dollars.
Cost Comparison
- Passive Installation (During Building): $300 - $600. It's incredibly cheap during the drywall stage before walls are painted.
- Active Installation (Retrofit on existing home): $1,200 - $1,800. Labor-intensive because they must core concrete and hide pipes.
- Activating a Passive System: $250 - $450. Adding the fan to an existing stack.
- Annual Electricity: The fan draws 40-80 watts, costing about $40 to $70 per year on your electric bill. Passive is $0.
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