What the problem is
A radon system that looks correct is not the same as a radon system that works. Suction can be insufficient for the soil, a suction point can be poorly placed, an unsealed sump or floor-wall joint can short-circuit the vacuum, or the fan can be under-sized. None of these are visible. Only a measurement after the system runs tells you what actually happened to the concentration in the house.
When verification testing is needed
- Immediately after any new mitigation system is installed.
- After a fan replacement or a change to the pipe routing.
- After a system repair or the addition of a suction point.
- When a buyer or lender requires documentation that a system is effective.
- Every two years as a routine confirmation that performance has held.
How the test is performed
- 1The system runs continuously for at least 24 hours before the test begins.
- 2Closed-house conditions are established 12 hours in advance.
- 3A continuous radon monitor is placed on the lowest lived-in level, in the same general area as the original test where possible.
- 4The measurement runs a minimum of 48 hours with hourly logging.
- 5The report compares pre- and post-mitigation values and records fan operation and manometer reading.
Expected timeline
| Step | Timing |
|---|---|
| System runtime before testing | 24 hours minimum |
| Closed-house period | 12 hours before start |
| Measurement | 48 hours |
| Report delivered | Same day the monitor is retrieved |
What result to expect
A properly designed active sub-slab system in a typical home should bring the level well below 4.0 pCi/L, and most land under 2.0 pCi/L. If the post-mitigation number is still elevated, the honest answer is that the design needs revision — commonly an additional suction point, a higher-capacity fan, or sealing that was missed.
EPA radon action levels
Scale shown in picocuries per liter (pCi/L).
Green is at or below the typical US indoor average. Amber is the range where the EPA suggests considering mitigation. Red is at or above the 4.0 pCi/L action level, where the EPA recommends fixing the home.
What affects the cost
- Whether the test is bundled with the installation or ordered separately.
- Number of test locations for multi-foundation homes.
- Continuous monitor versus lab-analyzed passive device.
What happens after the test
You receive a document that states the pre-mitigation level, the post-mitigation level, the device used, and the test conditions. Keep it with your home records — it is the single most useful document you can hand a future buyer, and it is what turns 'there is a system' into 'the system works.'
Related services
Keep learning
- EPA Radon Action Levels ExplainedTwo numbers drive nearly every radon decision: 4.0 pCi/L, where the EPA recommends action, and 2.0 pCi/L, where it suggests considering it. Here is what sits behind them.
- How Radon Mitigation Actually WorksA mitigation system does not filter radon. It reverses the pressure difference that pulls soil gas into your home in the first place.