Equipment guide
Negative air machine vs air scrubber
They are often the same piece of equipment. What changes is where the clean air goes.
Side by side
| Air scrubber | Negative air machine | |
|---|---|---|
| Airflow | Draws air in, filters it, returns it to the same room | Draws air in, filters it, exhausts it outside the containment |
| Main goal | Lower the airborne particle count | Keep contaminated air from escaping the work area |
| Setup | Free-standing, no duct needed | Lay-flat duct through a window, door or barrier port |
| Checked with | Particle counter, ACH math | Manometer: about −0.02 in. w.c. (−5 Pa) |
| Typical jobs | Post-cleaning air cleanup, odor, occupied rooms | Mold remediation, asbestos and lead abatement, healthcare construction |
Why the same unit can do both
Most commercial HEPA air scrubbers have an inlet on one side and a duct collar on the outlet. Run it loose in the room and it is a scrubber. Attach duct and route the exhaust out of the containment and it becomes a negative air machine, because the containment is now losing more air than it takes in. Variable-speed units make the switch easier — high speed to establish pressure, lower speed for quiet scrubbing.
When you need negative air
- Contaminants must not spread to occupied parts of the building — mold remediation, abatement, hospital work.
- The project specification or a clearance test requires a documented pressure differential.
- You are demolishing contaminated material, which releases far more particles than cleaning does.
If you only need to clean the air in a room after the work is done, or reduce odor in an occupied space, a scrubber recirculating in place is simpler and keeps conditioned air in the building.
How big?
Size both the same way: room volume times target air changes per hour, divided by 60, then allow for filter and duct losses. The air scrubber sizing calculator does this and gives you a unit count. For negative air, a well-sealed containment reaches pressure at that airflow; a leaky one needs more.
CFM = volume (ft³) × ACH ÷ 60 ÷ (1 − loss)Affiliate link. We may earn a commission at no cost to you.
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