Air scrubber calculator
Work out how many HEPA air scrubbers a mold, Category 3 water or demolition work area needs from its size and the air changes an hour you want, with the equipment days for the estimate.
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Work area
How the number of air scrubbers is worked out
The volume of the work area is the length times the width times the ceiling height of each room inside the containment, added together. Only the contained space counts: a scrubber cleans the air it can reach.
Air changes an hour (ACH) is how many times the scrubbers move the whole volume of air through their filters in an hour. The airflow needed is the volume in cubic feet times the ACH, divided by 60 to turn it into cubic feet a minute (CFM). Divide that by one unit's CFM and round up to whole scrubbers. The calculator starts at 4 air changes an hour and 500 CFM units; change both to match your equipment and the job.
Take a 32' × 28' basement and a 10' × 8' laundry room with 8' ceilings: 7,808 cubic feet. At 4 ACH that is 7,808 × 4 ÷ 60 = about 521 CFM, so two 500 CFM scrubbers, which together give about 7.7 air changes an hour.
Airflow ratings are usually measured with clean filters and nothing attached. As the pre-filter and HEPA filter load, and once lay-flat duct is attached for negative air, the real airflow drops. Many contractors plan on less than the rating: type a lower CFM to allow for it.
These are the same 4 air changes an hour and 500 CFM as the HEPA air scrubber line in vPlan AR's Water mitigation pack. The pack adds scrubber days room by room; this calculator sizes the whole contained area, since one scrubber can serve several rooms inside the same containment. Either way it is a starting count: the remediation plan or protocol for the job decides the real setup.
Tips
- Size for the space inside the containment, not the whole house, unless the whole house is the work area.
- For negative air, duct the exhaust out of the containment and check that the poly is drawn in; use a manometer if the protocol asks for a pressure reading.
- Change pre-filters often: a loaded pre-filter cuts the airflow and shortens the life of the HEPA filter.
- Keep the scrubbers running through cleaning until the post-remediation check, if the job has one, and log the days for the invoice.
Do this from a scan instead
Scan the work area or draw it, tag the damage, and on Pro the Water mitigation pack in Scope adds HEPA air scrubber days to each room from its volume, along with air movers and dehumidifiers. The scope and cost estimate export to PDF, CSV or Excel with the codes and formulas.
Frequently asked questions
How many air scrubbers do I need for 1,000 square feet?
With 8' ceilings, 1,000 square feet is 8,000 cubic feet. At 4 air changes an hour that needs 8,000 × 4 ÷ 60 = about 533 CFM, so two 500 CFM scrubbers: one alone gives only 3.75 air changes an hour.
How do you calculate air changes per hour?
Multiply the airflow in CFM by 60 and divide by the room volume in cubic feet. One 500 CFM scrubber in a 6,000 cubic foot area gives 500 × 60 ÷ 6,000 = 5 air changes an hour, at its rated airflow.
How many air changes per hour for mold remediation?
There is no single figure everyone uses. 4 air changes an hour is a common minimum for a contained work area, and many remediators run more. If the remediation plan or protocol for the job gives a figure, use that.
What is the difference between an air scrubber and a negative air machine?
Often it is the same HEPA machine set up two ways. As an air scrubber it filters the air and returns it to the room. As a negative air machine its exhaust is ducted out of the containment, so the work area is kept at lower pressure and dust and spores are drawn in, not pushed out.
Guides
- Mold Remediation Documentation Checklist for ContractorsMold jobs get questioned more than most. This checklist covers what to record before, during and after remediation, and how to keep it organized room by room on a measured floor plan.
- Water Damage Categories and Classes Explained: Category 1–3, Class 1–4Every water loss gets a category (how contaminated the water is) and a class (how much is wet and how hard it is to dry). Here is what each one means, how to work out the class from a room's measurements, and how both change the scope.
- How to Create a Water Damage Scope-of-Work Report from a Phone ScanScan the affected rooms, tag the damage, and export a professional scope-of-work report — with floor plan, room-by-room condition schedule, and photos — straight from your iPhone.