Post-Mitigation Retesting in Salt Lake City, UT

An Installed System Proves Nothing

This is the whole argument for retesting, and it is worth stating bluntly. A mitigation system that is working and a mitigation system that is failing look exactly the same from the garden. Both have a white pipe on the wall. Both have a fan that hums. The manometer next to the riser tells you the fan is moving air — it does not tell you the pressure field reaches the far corner of the basement, and it certainly does not tell you what the air in the house is measuring. The only evidence that exists is a second reading.

When It Runs

A post-mitigation test goes in after the system has been running continuously for at least twenty-four hours, and it runs for the usual 48 under the same closed-house conditions as the original. Testing it the hour the fan is switched on measures a house mid-transition and produces a number that means very little. Matching the conditions to the original measurement is what makes the two readings comparable, and comparability is the entire point of the exercise.

If It Has Not Come Down Far Enough

Sometimes it has not, and that is a normal part of this work rather than a scandal. The usual causes are known: the pressure field is not reaching part of the slab, a second sub-slab area was never connected to the first, a seal has been missed, or the fan is undersized for the ground it is pulling against. On the tighter west-side soils the first of those is the common one. The response is diagnosis, adjustment and another test — an additional suction point, more sealing, or a different fan — and that is the job rather than a change order.

Systems Somebody Else Installed

We will test an existing system regardless of who put it in, and it is a sensible thing to do when you buy a house that already has one. A system installed a decade ago may have had a fan fail silently, had an extension built over a suction point, or had its discharge altered during a roof job. Fans are consumable parts with a finite life. Nothing about the age of the pipe tells you the current reading, and where a system needs work rather than replacement that is covered under system repair.

Testing Again Later

Even a system that was verified and is still running deserves a fresh reading every couple of years, and after anything that changes how the house handles air — a new furnace, replacement windows, a basement finished out, an extension, or significant foundation work. Buildings are not static and neither are their readings. The original measurement is described on the testing page.

How long does it take? The same 48 hours, run at least 24 hours after the fan has been switched on so the sub-slab pressure field has settled.

Questions People Ask First