A West Chester new build with a passive radon stack: when fan-only activation is the right answer

The setup

A 2018 home in West Chester, 2,650 sqft, full unfinished basement, slab-on-grade attached garage. The builder had included radon-resistant new construction (RRNC) features. The home had a 4-inch PVC vent stack stubbed through the slab, routed up through a utility-room chase, terminated through the roof with a proper boot. Capped at the top with a PVC cleanout plug.

The buyers ran a hardware-store charcoal kit during the third month after move-in, placed in the basement family room. Result: 5.2 pCi/L. EPA action level is 4.0. They called our dispatch line to ask why the stack the builder installed wasn't doing its job.

Why "passive" rarely clears the action level in Greater Cincinnati

A passive radon stack relies on stack effect alone. Warm air inside the home rises and exits through upper-level penetrations, creating slight negative pressure at the foundation that pulls soil gas up the stack instead of into the home. In theory, a properly sealed slab and well-routed passive stack moves enough soil gas out to keep the home below 4.0 pCi/L.

In practice, a passive stack often falls short. The reasons:

1. Natural draft varies with the weather. The pull on a passive stack depends on the temperature difference between inside and outside, so it is weakest when that difference is small. 2. EPA's own figures favor a fan. EPA's Consumer's Guide to Radon Reduction rates passive subslab suction at typical reductions of 30 to 70 percent, compared with 50 to 99 percent for active subslab suction. 3. Soil gas varies by lot. Ohio Department of Health test data shows about 37 percent of reported Butler County tests above 4.0 pCi/L, so many lots start high enough that a partial reduction is not enough.

That is why EPA says every new home should be tested after occupancy, even if it was built radon-resistant, and why a passive stack is best treated as a head start for an active system rather than a finished one.

The on-site assessment

The Cincinnati-area mitigator confirmed the existing stack was correctly routed: through-slab penetration sealed properly, no offsets or 90-degree elbows that would impede airflow, terminated above the roofline at proper height (above the eave plus 12 inches per IRC). The stack diameter met current code. The home had no crawl space, no sump pit, and no obvious slab cracks beyond hairline settling.

The diagnosis was simple: the passive stack just needed a fan. Adding suction would convert the stack from "moves whatever air stack-effect can pull" to "actively pulls 130-140 cubic feet per minute of soil gas to the roofline."

The quote

$850 fixed, including: 1. Cut and remove the existing PVC cleanout cap 2. Install an inline radon fan (Radonaway RP145 (rated up to 166 CFM at 0" w.c.; typical operating flow ~100 CFM at 1.0" w.c.)) in the attic chase about 12 inches above the second-floor ceiling line (rated location for fan placement per ANSI/AARST SGM-SF-2023 standards) 3. Reconnect the stack above and below the fan with foam-and-clamp couplings 4. Install a manometer in the basement at the bottom of the stack with a labeled fan-failure indicator 5. Run a dedicated 15A electrical circuit from the basement panel up to the fan location 6. 48-hour post-install verification monitor with closed-house-conditions documentation 7. 12-month follow-up retest

For comparison, a complete new-system install on a home without an existing stack runs $1,200-$2,400. Activation of an existing passive stack is typically $700-$1,200.

Install day

Crew on site at 8:00 AM. Stack cap removed and fan position located by 8:45. Electrical run from basement panel to attic took about 90 minutes (the home had reasonably accessible chases). Fan mounted and wiring connected by 11:00. Manometer placement and labeling done by 11:45. Power up at 12:00 noon. Initial manometer reading: 0.85 inches of water column of negative pressure, healthy for this stack length and fan model. Total time on site: 4 hours, well under the quoted 5-hour scope.

The 48-hour retest

Continuous radon monitor placed in the basement family room (same location as the original charcoal kit). Closed-house conditions documented and signed by the homeowner. 48 hours later:

1.1 pCi/L average. Down 79% from pre-activation. Below the 2.0 pCi/L EPA-recommended post-mitigation target.

What the homeowner paid

Total: $850. Compared to the $1,200-$2,400 alternative of installing a new system from scratch on a non-RRNC home, this homeowner saved $350-$1,550 because the builder's passive stack provided the routing infrastructure for free. Annual electricity for the fan: about $95 on Duke Energy residential rates.

What to do if your home has a passive radon stack

Look for the passive stack first. Some newer homes in Mason, West Chester, Loveland, and Milford subdivisions were built with one, depending on the builder. Where it exists, the stack is visible as a 3-inch or 4-inch PVC pipe rising through a closet or utility-room chase, sometimes terminated visibly through the roof. If you can see a stack and your radon test reads above 4.0 pCi/L, fan-only activation is almost always the right answer.

Things to confirm with the local mitigator during the assessment: - The existing stack diameter (must be 3 inches or 4 inches; not all builders meet code) - The stack routing (must terminate above roofline; some builders leave inadequate clearance) - Slab penetration sealing (must be soil-gas-tight; 1990s-2000s builds sometimes leak) - Existing sump pit configuration (sealed lid + integration into suction is bonus value)

If any of those flags come back wrong, the activation quote may grow toward the $1,200 end of the range, but it is still cheaper than a new install from scratch.