Negative air machine

What it means

A negative air machine is a fan unit fitted with a HEPA filter. During remediation it is ducted to pull air out of the sealed work area and push it, filtered, outside the building.

Pulling air out makes the pressure inside the work area slightly lower than in the rest of the house. Air then leaks in through any gaps, not out, which keeps spores and dust from spreading. EPA’s remediation guide says full containment “must be maintained under negative pressure,” and that this can be done with a HEPA-filtered fan unit exhausted outside.

Why it matters to your home and your bill

Negative air is one of the clearest signs that a mold job is being done properly. Controlling pressure differentials is one of the competencies the IICRC lists for its Mold Remediation Specialist credential. Ask how the company will confirm the work area stays under negative pressure, how often it checks, and whether it will record those checks. Equipment is usually billed by the day, so the number of machines and days should match the size of the work area. Our mold remediation process page explains the full setup.