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.
- 0.4pCi/LOutdoor average
- 1.3pCi/LUS indoor average
- 2.0pCi/LConsider action
- 4.0pCi/LEPA action level
- 10+pCi/LWell above action level
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.