Existing systems
Passive Radon System Activation
Some newer homes were built with radon-resistant piping already in place. If a test comes back elevated in one of those homes, the question is whether that existing pipe can become an active, fan-driven system — and that is an evaluation, not a foregone conclusion.
What a passive system is
A passive system is a sealed vent pipe running from beneath the slab up through the building and out above the roof, installed during construction. It relies on the natural stack effect: warmer air rising in the pipe creates a slight draw.
That draw is weather-dependent and unverified. There is no fan and usually no indicator showing whether anything is happening.
The scenario this page addresses
The home already contains passive piping, a radon test has come back elevated, and the homeowner wants to know whether adding a fan solves it. Frequently it does — but only after a professional confirms the pipe is suitable for the job it would then be asked to do.
What gets inspected before a fan is added
- Where the pipe originates beneath the slab, and how it was terminated below.
- Whether the sub-slab connection can support the airflow an active system needs.
- Pipe diameter, material and whether joints are properly sealed.
- The full routing path, including sections hidden in walls or the attic.
- Whether the exhaust terminates above the roofline and away from openings.
- Whether the sub-slab area communicates well enough for one point to serve the foundation.
- Access and a suitable location for the fan outside occupied space.
- Availability of a code-compliant electrical supply.
What activation involves
| Step | What happens |
|---|---|
| Evaluation | The existing pipe and sub-slab conditions are assessed, often with diagnostic measurements. |
| Fan selection | A fan is chosen to match measured sub-slab conditions rather than pipe size alone. |
| Installation | The fan is fitted into the pipe outside occupied space, with sealed connections. |
| Monitoring | A manometer or equivalent indicator is added so operation can be observed. |
| Electrical | A suitable circuit and disconnect are installed to code. |
| Verification | A post-activation radon test documents the result. |
Electrical requirements
A radon fan runs continuously and needs a permanent, code-compliant supply — not an extension cord. Where a passive pipe was roughed in, an electrical junction may already have been provided nearby; where it was not, the electrical work becomes part of the scope and the price.
Testing after activation
Once the fan is running and conditions have stabilized, a follow-up test confirms the outcome. If the level remains elevated, the finding usually concerns suction coverage beneath the slab rather than the fan itself.
Cost factors
- Whether the existing pipe is usable as installed or needs rework.
- Fan location, access and mounting.
- Electrical supply — existing junction versus new circuit.
- Whether an additional suction point is required.
- Monitoring device and any labeling or documentation work.
Request a passive system evaluation
Share your test result, foundation type and project details. We pass your request to independent radon professionals — we do not perform the work ourselves.