Some of the most important equipment on a mold remediation or water damage job is also the least dramatic. It does not pump water or roar like a drying fan. It sits quietly in a corner or at the edge of a plastic enclosure, drawing air through a filter. HEPA air scrubbers and negative air machines protect the rest of a building while contaminated materials are cleaned or removed, and they protect the people doing the work.
This article explains what these machines do, how HEPA filtration works, the difference between scrubbing air and creating negative pressure, and how professionals decide how many units a space needs. It also covers the practical details of setup and filter changes that determine whether the equipment actually does its job.
What this covers
- What an Air Scrubber Does
- What HEPA Filtration Means
- Airflow Ratings and Air Changes
- Scrubbing Versus Negative Air
- How Containment Works With Negative Air
- Where These Machines Are Used
- Calculating How Many Units a Space Needs
- Filters, Pre-Filters and Maintenance
- Setup Details That Matter
- What Equipment Discussions Often Miss
- Short Answers on Air Scrubbers
What an Air Scrubber Does
An air scrubber is a portable filtration machine. A fan draws air from the room through a series of filters and blows the cleaned air back out. The filters capture particles such as dust, mold spores, soot and debris created by demolition. Running an air scrubber lowers the concentration of airborne particles in the work area and reduces the amount that settles on surfaces.
Air scrubbers are sometimes confused with air purifiers sold for home use. The principle is similar, but professional units move much more air, have heavier construction and are designed to run continuously on job sites.
What HEPA Filtration Means
HEPA stands for high-efficiency particulate air. A true HEPA filter is designed to capture at least 99.97 percent of particles 0.3 microns in diameter, a size often cited because it is among the hardest for filters to trap. Larger and smaller particles are generally captured at even higher rates.
Mold spores typically range from a few microns to tens of microns in size, which puts them well within the capability of HEPA filters. One Los Angeles equipment provider describes the Dri-Eaz Defender HEPA 500 air scrubber as filtering at 500 cubic feet per minute and capturing particles as small as 0.3 microns, including mold spores, asbestos fibers and fine dust.
Airflow Ratings and Air Changes
Air scrubbers are rated by airflow, usually in cubic feet per minute, often shortened to CFM. Airflow determines how quickly the machine can process the air in a room.
Professionals often think in terms of air changes per hour: how many times the entire volume of air in a space passes through the machine each hour. The calculation is simple. Multiply the machine’s CFM by 60 to get cubic feet per hour, then divide by the room’s volume in cubic feet.
|
Example |
Calculation |
Result |
|
Room volume |
20 ft x 15 ft x 8 ft |
2,400 cubic feet |
|
Air scrubber at 500 CFM |
500 x 60 |
30,000 cubic feet per hour |
|
Air changes per hour |
30,000 / 2,400 |
12.5 air changes per hour |
In practice, real airflow is lower than the rated figure once filters load with dust and ducting is attached, so professionals build in a margin.
Scrubbing Versus Negative Air
The same machine can often be used in two ways.
When used as a scrubber, the machine sits inside the room and recirculates the air, filtering it repeatedly. This reduces airborne particles but does not control where air flows.
When used as a negative air machine, the machine exhausts filtered air out of the contained work area, usually through a duct to the outdoors or to another part of the building. Because more air leaves the containment than enters it, the air pressure inside drops slightly below the surrounding areas. Air then flows into the work area through any gaps rather than out of it, which keeps contaminants from escaping.
|
Mode |
Air path |
Main purpose |
|
Recirculating scrubber |
Room air in, filtered air back to the same room |
Lower particle levels in the space |
|
Negative air |
Room air in, filtered air exhausted outside containment |
Keep contaminants from spreading |
Some jobs use both: negative air machines to control the containment and additional scrubbers in adjacent areas to clean any particles that escaped before containment was built.
How Containment Works With Negative Air
Containment is typically built from plastic sheeting taped and sealed to floors, walls and ceilings, with a zippered or flap entry. Negative air turns that enclosure into a controlled space. A visible sign that it is working is that the plastic walls bow slightly inward.
Containment and negative air work together. A well-built enclosure with no negative air can still leak contaminants when people move in and out. A negative air machine without a good enclosure pulls air from everywhere, not just the work area. Both need to be in place.
Where These Machines Are Used
Air scrubbers and negative air machines appear on many kinds of jobs:
- Mold remediation, to control spores during removal and cleaning
- Water damage restoration, especially when wet drywall and insulation are removed
- Sewage and other contaminated water cleanups
- Fire and smoke restoration, to capture soot
- Renovation and demolition, to control construction dust
- Some regulated abatement work, under the specific rules that apply to it
In each case, the goal is the same: keep what is disturbed in the work area from reaching occupants and clean parts of the building.
Calculating How Many Units a Space Needs
Professionals typically start with the volume of the containment area and a target number of air changes per hour, then divide by each machine’s effective airflow. Larger or more heavily contaminated jobs call for more air changes and therefore more units or higher-capacity machines.
A few other factors adjust the estimate: how dusty the work will be, how often people will enter and leave, whether ductwork is needed to exhaust air, and whether the space has high ceilings or complex layouts that trap air. Many jobs add a unit beyond the minimum for margin.
Filters, Pre-Filters and Maintenance
Air scrubbers typically use several stages of filtration. A coarse pre-filter catches large debris. An intermediate filter captures medium particles. The HEPA filter handles the finest particles. Pre-filters are inexpensive and are changed often, sometimes daily on dusty jobs, to protect the more expensive HEPA filter and maintain airflow.
Filters that are clogged reduce airflow, which lowers air changes and weakens negative pressure. Many units have indicator lights or gauges that show when filters need attention. Used filters from mold or contaminated jobs are bagged and disposed of carefully.
Setup Details That Matter
Small setup choices affect performance. Machines should sit where they can draw air from across the work area rather than tucked into a corner. Exhaust ducts should be as short and straight as possible, since long or kinked ducts reduce airflow. Electrical circuits must handle the load of several machines along with dehumidifiers and air movers.
Some units are designed to be stacked or daisy-chained electrically, which simplifies setup on larger jobs. Planning the layout before the equipment arrives saves time on the first day.
Noise and heat are practical considerations as well. Air scrubbers produce a steady hum that can be noticeable in occupied homes and offices, and several machines running together raise the temperature of a small room. Placing units where the noise is least disruptive, and checking room temperature during the first day of operation, helps keep the job site workable for everyone.
What Equipment Discussions Often Miss
Discussions of air scrubbers often focus on the HEPA filter itself. They tend to miss airflow in real conditions. A HEPA filter only helps if enough air passes through it, and airflow drops as filters load and ducts lengthen.
They also miss the difference between scrubbing and negative pressure. Running a scrubber inside a room lowers particle counts but does not stop contaminants from drifting out through open doors.
Finally, discussions rarely mention the end of the job. Machines are usually left running for a period after work stops, so that particles still in the air are captured before containment is removed and clearance testing takes place.
Short Answers on Air Scrubbers
Contractors and property owners comparing remediation equipment hire in Los Angeles can ask about airflow ratings, filter types and available ducting. LA Restoration Rentals, listed on its Google Business Profile, is one of the local suppliers renting HEPA air scrubbers, including the Dri-Eaz Defender HEPA 500 and an Abatement Technologies negative air unit, alongside dehumidifiers and air movers, by the day across Los Angeles County.
What does HEPA mean?
High-efficiency particulate air, a filter designed to capture at least 99.97 percent of 0.3 micron particles.
What is negative air?
Exhausting filtered air out of a contained area so air flows in, not out, keeping contaminants inside.
How are air changes per hour calculated?
Multiply CFM by 60 and divide by the room’s volume in cubic feet.
How often are pre-filters changed?
Often daily on dusty jobs, to protect the HEPA filter and maintain airflow.
HEPA air scrubbers and negative air machines are the quiet safeguards of remediation and restoration work. Sized correctly, set up carefully and maintained throughout the job, they keep contamination where it belongs and protect everyone else in the building.
