Restoration contractors ask us the same questions every day: how many air movers does this room need, how many dehumidifiers, and what will the rental run? Here are the straight answers, with the IICRC S500 math behind them. If you’d rather skip the arithmetic, our free water damage equipment calculator does all of it in about thirty seconds.
The IICRC S500 standard puts it at one air mover per room as a baseline, plus one for every 50 to 70 square feet of wet floor, plus one for every 100 to 150 square feet of wet wall above the two-foot line. In practice a standard 12 by 12 bedroom with a saturated floor takes about four air movers. Add offsets, closets, and bathrooms as their own rooms — each one needs at least a unit of its own because air won’t turn corners for you.
Class of loss drives the count. A Class 1 loss where only part of the floor is wet needs far fewer units than a Class 3 where water came from overhead and the walls and ceiling are saturated.
The working benchmark is one large LGR dehumidifier per 1,000 square feet of affected floor on a moderate Class 1 loss, tightening to one per 700 square feet at Class 2, one per 500 at Class 3, and one per 250 square feet for Class 4 bound-water specialty drying where moisture is trapped in hardwood, plaster, or concrete.
Two rules override that math. First, keep roughly one dehumidifier for every four air movers running — air movers push moisture into the air, and your dehumidification has to keep up or you’re just moving wet air around. Second, every sealed drying chamber needs its own dehumidifier, no matter how small it is. A closed-off bathroom can’t share a unit with the living room.
The S500 also provides a volume-based method: divide the affected cubic footage by the class factor (100 for Class 1, 50 for Class 2, 40 for Class 3 and 4) to get required pints per day, then divide by your unit’s AHAM rating. Our calculator will run it either way.
At National Drying Equipment, an extra-large LGR dehumidifier rents for $60 a day or $300 a week. Centrifugal air movers are $12 a day or $60 a week, axial air movers $15 a day, and HEPA 500 air scrubbers $85 a day or $305 a week. Three-day minimum on all rentals.
For a real-world number: a single saturated 12 by 12 room running four air movers and one dehumidifier for three to five days lands somewhere around $325 to $550 in equipment. A whole-floor Class 3 loss runs into the thousands. Call (800) 213-0638 for an exact quote on your job.
Any time the water is contaminated. Category 2 grey water — washing machine overflow, dishwasher discharge, tub drains — warrants roughly two air changes per hour of HEPA filtration. Category 3 black water from sewage or rising flood water calls for about four air changes per hour, along with containment and full PPE. Clean Category 1 supply-line water generally doesn’t need scrubbers unless the job sat long enough to grow something.
To size them: multiply the room’s cubic footage by the air changes per hour you need, divide by 60, and that’s the CFM your filtration has to move. Divide by your scrubber’s rating — 500 CFM for a HEPA 500 — for the unit count.
Typical field ranges run two to three days for a Class 1 loss, three to five days for Class 2, four to six for Class 3, and five to seven days for Class 4 specialty drying. Category 3 contamination usually adds a day for demolition and containment.
Those are planning numbers, not promises. The S500 deliberately doesn’t fix drying times, because the only thing that actually determines when you pull equipment is daily moisture readings showing materials have hit dry standard. Document those readings every day — it’s what protects your invoice when an adjuster questions the equipment duration.
Almost always because the scope has no formula behind it. “We used sixteen air movers” invites an argument. “Sixteen air movers per IICRC S500 placement guidance — one per room plus one per 70 square feet of wet floor across four affected rooms” ends one. Show the standard, show the math, and back the duration with a daily drying log carrying temperature, relative humidity, GPP, and moisture content readings.
Insurance reimburses the same equipment line whether you own the machine or rent it, so ownership doesn’t earn you more per job — it just ties up capital. Renting lets you scale a fleet up for a storm event and back down when it passes, without carrying idle machines, maintenance, or storage between losses. Read the full breakdown on our why rent versus buy page.
Yes. National Drying Equipment processes orders the same day and delivers same or next day throughout the Eastern United States — Florida to Michigan, Texas to New England. We answer 24 hours a day, 7 days a week, including holidays, because water losses don’t wait for business hours. We keep hundreds of air movers and LGR dehumidifiers staged and ready to go out the door.
Call (800) 213-0638 or size your job with the calculator first and tell us what you need.
