Air Scrubber: What It Does and What It Cannot Do

Quick answer

An air scrubber is a portable filtration machine that draws room air through a series of filters, such as a pre-filter and a HEPA filter, and returns it to the room to remove airborne particles while restoration work is under way.

It cleans the air. It does not dry a building, fix a leak, remove the source of mold or make a contaminated space safe on its own. EPA says air cleaners are a supplement to source control and ventilation, not a replacement.

Quick facts

The key facts about Air Scrubber, with sources:

What it filters: Airborne particles; carbon filters can be added for odors ¹
Typical stages: Pre-filters, an optional carbon filter and a final HEPA filter ¹
HEPA definition: At least 99.97% removal of 0.3-micron particles, per EPA and the DOE handbook ⁵⁶
Air scrubber or negative air machine: A scrubber recirculates air in the room; a negative air machine ducts air out of a sealed containment ¹
Sizing idea: Air changes per hour: room volume times the target, divided by 60, gives CFM ¹
EPA position: Filtration can be an effective supplement to source control and ventilation, and cannot remove all pollutants ³
On mold: Portable air cleaners do not address the cause of mold and musty odors ⁴

Key takeaways

An air scrubber filters particles out of room air through stages, ending in a HEPA filter ¹.
It is a supplement. EPA says the most effective approach is to reduce or remove pollutant sources and ventilate, with filtration added on top ³.
It does not remove the cause of mold. EPA says air cleaners do not address the cause of mold and musty odors; the moisture must be fixed ⁴.
A scrubber recirculates air in a room. A negative air machine pulls air out of a sealed containment. They are not the same job ¹.
Sizing is arithmetic on room volume and air changes per hour, and the maker’s numbers are guidance, not a legal standard ¹.

What an air scrubber is, in plain English

Restoration work stirs up the air. Drying uses strong airflow. Demolition makes dust.

A manufacturer’s guide notes that the airflow needed for drying stirs up particles trapped in carpet or settled on materials, and that jobs involving sewage, mold or fire damage generate significant particulates ¹.

An air scrubber is a machine that pulls that air through filters and puts it back cleaner.

The Dri-Eaz guide puts it simply: an air scrubber is a portable filtration system that draws in air from the surrounding environment and passes it through a series of filters ¹. EPA calls the household version a portable air cleaner, designed to filter the air in a single room or area ³.

It is easy to expect too much. EPA states that filtration can be an effective supplement to source control and ventilation, and that air cleaners cannot remove all pollutants from the air ³. A scrubber cleans the particles that are airborne at that moment. It does not dry a wall or stop a leak.

Our pages on HEPA filtration and the negative air machine cover the filter and the containment version.

How an air scrubber works, step by step

The air scrubber stages follow the manufacturer’s guide ¹.

Air is drawn in. A blower pulls room air through the filter stack.
Pre-filters catch the large particles. The guide says pre-filters capture most larger particles, from visible down to about 10 micrometers, and extend the life of the more expensive final filter.
An optional carbon filter takes odors. Activated carbon adsorbs gas- and vapor-phase molecules that the nose detects as odors.
A HEPA filter catches the smallest particles. The final stage removes particles as small as 0.3 microns, and HEPA media is laboratory-tested to capture at least 99.97% of them at a set airflow.
Filtered air returns to the room. A plain air scrubber stands alone in the room with no ducting, and the air it filters is recirculated.
Filters are changed when loaded. The guide advises changing the primary filter between every job to avoid cross-contamination.

Layers What air passes through, in order

Pre-filtersLarger particles, in increasing efficiency
Optional carbon filterOdor and vapor molecules
HEPA filterFinal stage for the smallest particles
BlowerPulls air through and returns it to the room

Each stage protects the next. Without pre-filters, the HEPA filter loads sooner and airflow falls. Source: [1]

Air scrubber, negative air machine and household air cleaner compared

The two terms are easy to mix up. The manufacturer’s guide says the two restoration terms refer to very different applications.
Machine	How it is used	What it controls
Air scrubber	Stands in the center of a room with no ducting and recirculates the air it filters ¹	General air quality of the jobsite ¹
Negative air machine	Uses ducting to remove contaminated air from a sealed containment and exhaust it outside, creating negative pressure inside ¹	The spread of contaminants to other areas ¹
Household portable air cleaner	Designed to filter the air in a single room or area ³	Particles in that room; not every pollutant ³
Furnace or HVAC filter	Designed to filter air throughout a home ³	Whole-house particles, at the filter’s rating

Many scrubbers can become negative air machines

The guide says many air scrubbers can also be used as negative air machines, but this requires being ductable in and out, a sealed housing, precise airflow adjustment and a variable-speed blower to maintain containment ¹.

Example: sizing an air scrubber by air changes per hour

The method comes from the manufacturer’s guide: find the room’s volume, multiply by the air changes per hour (ACH) you want, and divide by 60 to get cubic feet per minute (CFM) ¹.

The room is the guide’s own example, 500 square feet with an 8-foot ceiling.

The ACH targets are illustrative: the guide recommends at least 6 as a general rule, and a sizing sheet from the same maker uses a minimum of 4 in its worksheet ¹².

The guide also says there are currently no standards for the minimum ACH for water damage restoration, and that existing ACH numbers come from other industries and vary widely ¹.

Step	At 6 ACH	At 4 ACH
Room volume	500 × 8 = 4,000 cubic feet	4,000 cubic feet
Cubic feet to filter per hour	4,000 × 6 = 24,000	4,000 × 4 = 16,000
Convert to CFM (divide by 60)	24,000 ÷ 60 = 400 CFM	16,000 ÷ 60 = about 267 CFM

Chart Clean air delivery rate for the same 450 CFM machine at three filter efficiencies

In the manufacturer’s illustration, a machine moving 450 CFM has a clean air delivery rate of 450 CFM with a true HEPA filter, 360 CFM with 80% efficiency and 0 CFM with no filtration.

Clean air delivery rate for the same 450 CFM machine at three filter efficiencies (cubic feet per minute of cleaned air)
Item	Value (cubic feet per minute of cleaned air)
99.97% (true HEPA)	450 CFM
80% efficiency	360 CFM
0% (no filtration)	0 CFM

Data period: Illustration in the Dri-Eaz Guide to Air Scrubbing, CADR section, read 2026-10-14

Source: [1]

This is the maker’s sizing arithmetic, not a code. The guide also warns that a machine’s CFM number says little about filtration quality, and that a filter that passes a laboratory HEPA test at a slow rate may not perform the same at the job airflow.

It recommends comparing machines by clean air delivery rate (CADR) where available ¹.

Where you see an air scrubber on a job

In the middle of the affected area. For water damage, the guide says to place the scrubber in the center of the affected area, and in large or divided spaces to use several units ¹.

Beside air movers and dehumidifiers. Drying airflow stirs particles, and the guide says a scrubber helps keep dirt from coating dehumidifier coils or clogging air mover intakes ¹. See air movers and the dehumidifier page.

In sewage, mold and fire jobs. Our service pages on mold remediation and sewage cleanup explain where containment and filtration fit.

On the invoice. Equipment appears by unit and by day. The cost guide explains how the line is built.

Ask what the scrubber is for

A good answer names the job: dust from demolition, particles from drying airflow or containment. “It is part of the package” is not a reason you can check.

What an air scrubber helps with, and what it does not

What it helps with

Reduces airborne particles stirred up by drying and demolition ¹.
Helps keep dust out of equipment. The guide says it captures debris that might coat dehumidifier coils or clog air mover vents ¹.
Adds a carbon option for odors ¹.
Works as a supplement to source control and ventilation, as EPA describes filtration ³.

What it does not do

Remove the cause of mold or musty odors. EPA says air cleaners do not address the cause ⁴.
Remove all pollutants, including all gases. EPA notes there are no widely used rating systems for portable cleaners that remove gases ⁴.
Dry the building, stop a leak or clean contaminated surfaces.
Replace containment. A recirculating scrubber does not keep contaminants from spreading to other rooms ¹.

Limits of air scrubbers

Source control comes first. EPA says the most effective way to improve indoor air is to reduce or remove pollutant sources and ventilate with clean outdoor air, with filtration as a supplement, and that no air cleaner or filter will eliminate all pollutants ³⁴.

For mold, the fix is to get rid of the moisture source and clean up the mold ⁴.

Particles only, mostly. EPA says there are no widely used rating systems for portable air cleaners designed to remove gases, and that activated carbon is the usual choice, working best in large amounts ⁴. A carbon stage helps with odors, but it is not proof that a gas is gone.

Lab ratings do not equal job ratings. The manufacturer’s guide warns that not all HEPA-media filters provide the same performance on the jobsite as in the laboratory, because airflow rate affects results ¹.

Placement matters. The guide notes that stale pockets of air can remain out of reach, and that several smaller units can serve a space better than one large unit ¹.

The air-change numbers are the maker’s guidance. The guide itself says there are no standards for minimum ACH in water damage restoration ¹.

What drives air scrubber cost, and how long filters last

We publish no prices and no source we loaded gives one. The cost drivers are the number of units, the number of days, filter changes and any ducting for containment.

Filters are a real part of the cost. The guide says the best practice is to clean the unit and replace pre-filters and the primary filter after every job, and that the cost of filters should be considered part of the cost of restoration ¹.

A carbon filter is optional and its life depends on the type and concentration of odor ¹.

For a household unit, the measure is CADR and the filter schedule in the manual. King County’s guidance suggests a CADR of 65 for every 100 square feet of room space, assuming an 8-foot ceiling ⁷. The estimate checker helps you review an equipment line, and the drying time tool shows what affects duration.

How a company runs one, and what you can do

The company runs the equipment. These steps follow the guide and give you things to check ¹. No permit is normally needed for a portable unit.

Start with a clean unit and new filters. The guide says to thoroughly clean the unit and replace filters after every job.
Place the unit in the center of the affected area so it draws surrounding air and returns filtered air to the same space.
Add units for large or divided areas to avoid stale pockets of air.
Run it while drying and demolition create particles. Change filters when pressure drop rises and filtration begins to suffer.
Ask what the unit is rated at and how the company sized it. The guide’s method uses room volume and air changes per hour.
At the end of the job, ask that filters are replaced and the unit cleaned before it goes to another site.

Care of a unit

Air scrubber upkeep points come from the Dri-Eaz guide and the King County health guidance for HEPA air cleaners ¹⁷.

Replace pre-filters as they load. Pre-filters may be replaced several times in the life of one primary filter.
Do not clean HEPA filters. A sizing sheet from the same maker says not to clean filters and to replace them when loaded or after use in any area with cross-contamination risk ².
Wear protection when changing filters. King County advises an N95 or KN95 mask, unplugging the unit and removing dirty filters outdoors or in a well-ventilated area ⁷.
Keep intakes clear. King County advises keeping walls, furniture and curtains away from the intake and outlet.
Keep a log. Record when filters were changed and when they are due.

Warning signs and when to call a professional

A musty smell that returns. EPA says air cleaners do not address the cause of mold and musty odors, so the moisture source is still there ⁴.
A scrubber used as a substitute for drying or repairs. It cleans air only.
Features that make ozone. EPA says to avoid portable air cleaners that intentionally produce ozone, and that no federal agency has approved them for use in occupied spaces ⁴.
Dirty filters never changed. A loaded filter cuts airflow and filtration.
Visible mold or sewage. That calls for professional containment and cleanup, not a scrubber alone.

A scrubber does not make a contaminated space safe

Never enter a flooded or fire-damaged building before it has been judged safe. Mold, sewage and fire residue need professional assessment and containment where the assessment calls for it. A filter machine does not remove the source, and one test cannot certify a building mold-free.

Standards, ratings and guidance

No law sets an air-change number for water jobs. The manufacturer’s guide says there are currently no standards for the minimum ACH on water damage restoration and that numbers come from other industries and vary by application and jurisdiction ¹.

HEPA is defined by a test. The DOE nuclear air cleaning handbook defines a HEPA filter by a minimum 99.97% removal of 0.3-micrometer particles, with a resistance limit and a rigid casing ⁶.

The guide says the industry follows recommended practices from the Institute of Environmental Sciences and Technology, which are not government regulations ¹.

Ratings for portable cleaners. EPA explains CADR as the measure of how many particles the cleaner can filter and the area it can serve ⁴.

Restoration standards. ANSI/IICRC S500 and S520 cover water and mold work. They are purchased voluntary standards, and this page does not reproduce them or say what they require about scrubbers ¹⁰.

Your contract. Equipment terms vary by company.

Air scrubber compared with related terms

Term	What it means	How it differs from an air scrubber
HEPA filter	A filter type rated 99.97% at 0.3 micrometers ⁵	A part of the scrubber, not the whole machine
HEPA vacuum	A vacuum with a HEPA filter, recommended by NIH for final cleanup after materials are dried ⁸	Cleans surfaces; a scrubber cleans air
MERV rating	Measures capture of particles from 0.3 to 10 micrometers, mainly for HVAC filters ⁵	A different rating system
Ozone generator	Intentionally produces ozone	EPA says avoid them ⁴
Dehumidifier	Removes vapor from the air ⁸	Dries air; a scrubber filters particles

Side by side Air scrubber vs negative air machine

Air scrubber

Stands alone in the room
No ducting; recirculates filtered air
Improves general jobsite air
Can run alongside drying equipment

Negative air machine

Ducted in and out of a sealed containment
Exhausts outside; creates negative pressure
Limits spread to other areas
Needs a sealed housing and variable speed

Source: [1]

Common myths about air scrubbers

Myth An air scrubber gets rid of mold.: Reality EPA says air cleaners do not address the cause of mold and musty odors. The moisture must be fixed and the mold cleaned up ⁴.
Myth Any “HEPA” label means the same thing on the job.: Reality The manufacturer’s guide says not all HEPA-media filters provide the same performance on the jobsite as in the laboratory ¹.
Myth A bigger CFM number means cleaner air.: Reality The guide says CFM tells little about filtration quality and recommends CADR ¹.
Myth An air scrubber and a negative air machine are the same.: Reality The guide says they are used for very different applications ¹.
Myth Ozone or ionizing features add safety.: Reality EPA says to avoid air cleaners that intentionally produce ozone and that no federal agency has approved them for occupied spaces ⁴.

Where you live changes the particles

The regional variable is outdoor air quality. King County’s guidance advises closing windows and doors while a HEPA cleaner runs during high outdoor pollution, such as wildfire smoke ⁷.

The same logic applies to restoration jobs in smoke-prone regions: a scrubber that recirculates indoor air works best with the space closed. Humid regions add a second issue.

EPA describes outdoor air with a dew point above 70°F in Miami through most of a typical year, so moisture control matters more than filtration for preventing mold there ⁹. Filtration is a supplement everywhere.

When an air scrubber matters, and what to do next

An air scrubber matters when drying or demolition stirs up dust, when someone is sensitive to particles, and when sewage, mold or fire residue is involved. It matters less on a small, clean water job that dries without demolition.

The next step is to ask what the scrubber is for and what is being done about the moisture source. See moisture control and mold prevention for the order that works, and how restoration works for the usual sequence of a job.

Decision guide Is an air scrubber the right tool?

If Dust or particles from demolition or drying: Then A scrubber can help; ask how it is sized
If A musty smell that keeps returning: Then Look for the moisture source; a scrubber will not fix it
If Contaminants must not reach other rooms: Then Ask about containment and negative air, not a plain scrubber
If A product claims ozone or ionization: Then Avoid it for occupied spaces, per EPA

Questions about Air Scrubber

What does an air scrubber do?

It draws room air through a series of filters, such as pre-filters and a HEPA filter, and returns it cleaner.

A manufacturer’s guide describes it as a portable filtration system that removes particles stirred up by drying and demolition.

It cleans the air at that moment and does not dry a building or fix a leak.

Does an air scrubber remove mold?

No. It can capture mold spores that are airborne, but EPA says portable air cleaners do not address the cause of mold and musty odors, which is moisture. The fix is to get rid of the moisture source and clean up the mold. A single filter or test cannot certify a building mold-free.

What is the difference between an air scrubber and a negative air machine?

An air scrubber stands alone in the room and recirculates filtered air. A negative air machine uses ducting to pull air out of a sealed containment and exhaust it outside, creating a slight vacuum inside so contaminants do not spread. The manufacturer’s guide says the two terms refer to very different applications.

How many air changes per hour does an air scrubber need?

The sources we loaded give guidance, not a rule. The manufacturer’s guide recommends a minimum of 6 as a general rule and says no standard sets a minimum for water damage restoration. A sizing sheet from the same maker uses a minimum of 4. Ask the company how it sized the unit for your space.

How do you size an air scrubber?

Multiply the room’s volume in cubic feet by the air changes per hour you want, then divide by 60 to get CFM.

For a 500 square foot room with an 8-foot ceiling, that is 4,000 cubic feet; at 6 changes per hour, 24,000 cubic feet per hour or 400 CFM. The guide also recommends comparing machines by CADR.

Is an air scrubber the same as a HEPA air purifier?

They share the HEPA filter. EPA calls household units portable air cleaners that filter a single room. Restoration scrubbers are built for tougher use, with pre-filter stages and higher airflow. HEPA means at least 99.97% removal of 0.3-micron particles under test, but job performance depends on airflow and fit.

Do air scrubbers remove odors?

Only with a carbon filter. The manufacturer’s guide says an optional carbon filter captures gas- and vapor-phase molecules the nose detects as odors, while EPA says there are no widely used rating systems for portable cleaners designed to remove gases. An odor that returns can mean the source is still there.

How frequently should filters be changed?

Change them when loaded and between jobs. The guide advises replacing pre-filters and the primary filter after every job to avoid cross-contamination and changing filters during a job when pressure drop rises. A sizing sheet says not to clean filters. Household units follow the maker’s manual schedule.

Are ozone-producing air cleaners safe?

EPA says to avoid portable air cleaners that intentionally produce ozone, and that no federal government agency has approved these devices for use in occupied spaces. Ask the company whether any equipment it plans to use produces ozone, and decline it in an occupied home.

Where should an air scrubber be placed?

For water damage, the manufacturer’s guide says to place it in the center of the affected area so it draws surrounding air and returns filtered air to the same space, and to use several units in large or divided spaces to avoid stale pockets. Keep walls and furniture away from the intake and outlet.

Sources

Legend Brands (Dri-Eaz), Guide to Air Scrubbing, retrieved October 14, 2026.
Legend Brands (Dri-Eaz), Air Scrubber Selection and Sizing Guide (HEPA 700 specification sheet, 2022), retrieved October 14, 2026.
U.S. EPA, Air Cleaners and Air Filters in the Home (page updated August 3, 2026), retrieved October 14, 2026.
U.S. EPA, Guide to Air Cleaners in the Home, 2nd edition (archived snapshot of epa.gov, 19 January 2025), retrieved October 14, 2026.
U.S. EPA, What is a HEPA Filter?, retrieved October 14, 2026.
U.S. DOE, DOE-HDBK-1169-2003 Nuclear Air Cleaning Handbook, Chapter 3: Filters for the Nuclear Industry, retrieved October 14, 2026.
King County Public Health, HEPA air cleaners (indoor air quality and mold), retrieved October 14, 2026.
National Institutes of Health, Moisture and Mold Remediation Standard Operating Procedures (2023), retrieved October 14, 2026.
U.S. EPA, Moisture Control Guidance for Building Design, Construction and Maintenance (EPA 402-F-13053, December 2013), retrieved October 14, 2026.
IICRC, ANSI/IICRC S500 Standard for Professional Water Damage Restoration (standard page), retrieved October 14, 2026.

Expert review

Written by the HyreRestore Research Desk. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.

How the numbers were checked: Machine descriptions, filter stages, sizing arithmetic, CADR illustration and the statement that no ACH minimum exists for water damage restoration come from the Dri-Eaz Guide to Air Scrubbing and a companion sizing sheet, which are manufacturer documents and not neutral research.

EPA statements are from its Air Cleaners page and the archived Guide to Air Cleaners in the Home (second edition). The HEPA definition is from DOE-HDBK-1169-2003 Chapter 3 and EPA.

The sizing example is the maker’s own worked method and is not a code. IICRC S500 and S520 are purchased and were not read, and the guide’s quotation of S520 air-change figures was not verified, so none is given. No prices and no durations are given.

Suggest a correction. We fix errors and say what changed.