How to choose a HEPA air scrubber for water-damage restoration (ACH, CFM, daisy-chain, UV-C)

Water-damage work puts particles in the air on purpose. Air movers strip dust, insulation, and microbial fragments off wet structure. If you are cutting drywall or disturbing mold, those particles need a destination other than the rest of the building. That destination is a HEPA air scrubber, ducted as a negative-air machine when the job is contained.

This is for IICRC water and mold contractors and facility managers who buy machines instead of renting every loss. Numbers below are manufacturer-published figures for SKUs Germaphobix stocks. No invented DOP tests. Germaphobix is the supplier, not a ranked “#1” contractor.

Start with cubic feet, not a square-foot badge

ACH = (CFM × 60) / room volume in ft³

CFM needed = (target ACH × ft³) / 60

A contained 20 × 15 × 8 ft room is 2,400 ft³. Four air changes per hour needs 160 CFM delivered; six ACH needs 240 CFM. That looks easy until you remember catalog CFM is usually clean-filter, short-duct. Load the HEPA, add flex, pinch layflat, and delivered air falls.

AlorAir’s Max 970 coverage line is 7,500 cubic feet at 750 CFM — volume, not floor area. 7,500 ft³ at 750 CFM is 6 ACH only if the machine is truly moving 750 CFM. PuriSystems lists the S1 at 1,100 sq ft and the S2 at 2,500 sq ft. Treat those as manufacturer area claims, then still run the ACH math on the contained volume.

Contractors commonly keep mold containments at several ACH with the outlet ducted out of the plastic so the space stays negative to adjacent rooms. IICRC S500/S520 are the standards; they do not collapse to one ACH for every Category 1 bath. Size up, then use variable speed so you are not beating poly off the walls.

Match CFM class to the truck

When two cabinets share 550 CFM, buy the collar that matches the flex on the truck. AlorAir: Max 870 uses a round 8 in exhaust; Pro 870 uses a rectangular exhaust and a 16 in intake (Max family is 14 in). Max 870 also publishes 2.8 in. H2O static. Those are the real 870 vs 870 differences — not CFM.

Daisy-chain is amp math

AlorAir: Pro 870 and Max 870 link up to 3 units on a 15 A UL-rated GFCI duplex at 2.5 A each. Three fans are 7.5 A before a 10.3 A dehumidifier. PuriSystems publishes “up to 3” on the S1 (also 2.5 A). The S2 is 5.5 A alone. BioMatrix does not publish a duplex. Add every nameplate on the string and leave headroom for a wet, high-amp dehu.

UV-C vs not

UV-C here is a lamp in the airstream. It does not vacuum spores off a stud. AlorAir puts a lamp in the box for Pro 870, Max 870, and Max 970. Max 770 highlights and box list omit it. Germaphobix’s S2 is the non-UV black unit; UV-C is the separate S2 UVIG SKU. If the RFQ requires UV-C, do not quote Max 770 or black S2. If the RFQ is HEPA CFM and collars, skip the lamp and buy pre-filters.

What “HEPA” means on these sheets

AlorAir PureAiro: MERV-10 pre-filter plus HEPA/activated carbon. The Max 870 spec PDF says up to 99.95% at 0.3 µm — use that on the Max 870, not an invented 99.97%. PuriSystems S2: 24 × 24 × 11.5 in HEPA/carbon and 99.97% of particles larger than 0.3 µm. BioMatrix: “HEPA MERV-13” and 0.3 microns; MERV-13 and true HEPA are different systems, so do not upgrade BioMatrix to 99.97% in a bid. Change pre-filters on dirty demo. For mold, AlorAir tells you to change filters between critical jobs so you do not drag contamination to the next house.

Negative air machine vs air scrubber

On a restoration truck these are often the same HEPA cabinet in two setups.

Scrubbing (recirculate): intake and exhaust both stay inside the work area. Air passes HEPA and returns to the room. Use this when you need particle capture without pulling outdoor makeup air through the containment.

Negative air (ducted exhaust): intake inside containment, exhaust ducted outside the plastic so the space stays slightly negative to adjacent rooms and dust stays in. Put a manometer on the poly. Catalog CFM does not prove pressure.

Same machine class. Different ducting. Collar sizes on Germaphobix AlorAir cabinets still apply (Pro 870: 16 in intake / 8 in exhaust; Max 770/870/970: 14 in / 8 in). Stack rotomolded cabinets for transport; do not use them as step stools.

PuriSystems S1 and S2 cannot ship to California. AlorAir lists CARB EO# G-20-259 and EPA Est. No. 99216-CHN-1; that establishment number is not a pesticide registration.

Germaphobix ships most items free in 2–3 days nationwide, (866) 312-1777. Own the filters. A cabinet without a pre-filter on the truck is a paperweight.

FAQs

Is a negative air machine different from an air scrubber?

Usually the same HEPA cabinet. Negative air means exhaust is ducted out of containment so the space stays under negative pressure to the clean side. Scrubbing means filtered air returns to the room.

Do I need a manometer for negative air?

For contained negative-air work, yes. A manometer on the poly shows whether the space is actually negative. Published CFM alone does not.

How many 550 CFM units for a 2,000 ft² house?

You cannot answer from square feet. Contained cubic footage only. A 2,000 ft² house at 8 ft ceilings is 16,000 ft³; four ACH is about 1,067 CFM delivered. You usually scrub contained rooms, not the whole house.

Does UV-C mean I can skip HEPA?

No. The filter captures. UV-C is extra.

Can I daisy-chain Max 970s like 870s?

“Up to 3” is explicit on the 870 pages. The 970 table lists the GFCI duplex. Confirm the 970 spec sheet before writing three-unit daisy-chain into an SOP.

Why not always buy the S2?

119 lb, 5.5 A, no CA shipping, 1-year PuriSystems warranty versus AlorAir’s 10-year language, and you still need small stackables for baths.

Shop related: Live HEPA scrubbers — AlorAir PureAiro Max 870, Pro 870, Max 770, Max 970, PuriSystems S1, S2, and HEPA 600 UVIG. Air movers for evaporation: Zeus 900 / Zeus Extreme.

Related: AHAM vs saturation dehumidifier pints.