Air Scrubber Calculator

CFM Required and unit count depend entirely on Room Volume and Target Air Changes/Hour, since those two figures determine how much air needs to move through the space regardless of what kind of filter medium is doing the filtering. Filter Type only changes how quickly the filter media itself becomes loaded and needs replacement — HEPA media handles particulates differently than carbon media handles gaseous VOCs and odors, so their typical service-life hours differ even when both are installed in units delivering identical airflow. These filter-life hours are representative planning baselines for each media type; they don't adjust for how contaminated the air actually is, how large the space is, or how many units are running, all of which affect how fast a filter actually loads in the field — treat the estimate as a starting point for budgeting replacement filters, not an exact schedule.

ANSI/IICRC S520 specifies 4 air changes per hour as the minimum within containment for general remediation — that's the one figure the standard itself sets. 6 or more ACH shows up widely in restoration trade and vendor guidance as a step up for more aggressive active remediation (heavier contaminant load, active demolition), but it isn't itself an S520-mandated number the way the 4 ACH minimum is. Treat 4 ACH as the standard's floor and 6+ ACH as common industry practice above that floor, not as a second IICRC-specified figure.

Since CFM Required scales directly with the volume you enter, underestimating volume by ignoring a taller section of ceiling will undersize your air-changes-per-hour rate for the space you're actually treating — you'll get fewer real air changes per hour than the number you set as your target. Calculate volume as square footage times the true average ceiling height for irregular spaces, or split a space with very different ceiling heights into sections and size each one separately for an accurate result.

500 CFM is used here as a representative nameplate capacity for a standard commercial HEPA air scrubber, but real units on the market commonly range from around 500 up to 2,000 CFM depending on model and size, so a job renting larger units could need fewer of them than this calculator's unit count suggests. This calculator also derates that nameplate figure to about 70% (roughly 350 CFM delivered per unit) to account for real-world airflow loss from filter loading and containment leakage rather than assuming a brand-new, unloaded unit performs at full nameplate CFM throughout the job. Check your actual equipment's rated CFM and derate it similarly if your units differ meaningfully from the 500 CFM assumption used here.