Free Tool For Restoration ContractorsThe Air Mover Calculator
Stop counting linear feet. Count wet surface. Then have the receipts when the adjuster asks why you put nine fans in a living room.
Area-method sizing built on Airmover Calculations in Structural Drying Projects, the IICRC S500 Consensus Body white paper, July 2014. Free, no signup on this page, and it prints. Every number it gives you comes with the formula behind it.
Fair warning before you use this. The white paper this thing is built on says right on
page one that it “is not, and should not be construed as, part of the industry standard of care.”
It points you back to the S500 itself. So this is a sizing aid for day one, not a substitute for the standard,
your meter, or your own eyes. Confirm against whichever S500 edition you are working under. If you paste a
number off this page into an estimate and cannot explain where it came from, that is on you, not on the
calculator.
page one that it “is not, and should not be construed as, part of the industry standard of care.”
It points you back to the S500 itself. So this is a sizing aid for day one, not a substitute for the standard,
your meter, or your own eyes. Confirm against whichever S500 edition you are working under. If you paste a
number off this page into an estimate and cannot explain where it came from, that is on you, not on the
calculator.
Dimensions
| Room | L (ft) | W (ft) | Offsets | Air movers | |
|---|---|---|---|---|---|
| TOTAL | 0 | ||||
Totals
Initial placement
0
air movers, day one
Total wet surface
0
square feet across all rooms, the basis for the count
2006 linear foot method
0
superseded, shown for comparison
This is an initial placement number, and that is the part everybody skips.
The paper is explicit that the count covers day one and that airflow gets adjusted throughout the project.
So place to this number, monitor, and step equipment down as the readings show rooms drying out. Write down
the reading and the date that triggered each change. A drawdown tied to a dated moisture reading is nearly
impossible to argue with. A drawdown tied to a schedule falls apart the second somebody asks where the
schedule came from.
The paper is explicit that the count covers day one and that airflow gets adjusted throughout the project.
So place to this number, monitor, and step equipment down as the readings show rooms drying out. Write down
the reading and the date that triggered each change. A drawdown tied to a dated moisture reading is nearly
impossible to argue with. A drawdown tied to a schedule falls apart the second somebody asks where the
schedule came from.
Estimate output
Room-by-room quantities and a variable formula for each, ready to paste into an estimating platform.
The reasoning
Why linear feet was always the wrong measurement
Water leaves a material at its face. Faces are measured in square feet. So when you size airflow off theperimeter of a room, you are measuring the shape of the box instead of how much wet stuff is in it. The
Consensus Body said it in one line:
Since evaporation occurs at the surface of materials, air movement needs to be related to and directed at wetHere is why it matters to you and not just to the nerds. The perimeter method fails in both directions. Big
surface area.
Airmover Calculations in Structural Drying Projects, IICRC S500 Consensus Body, July 2014, p.11
open great room with a wet field of floor? Small perimeter, not enough fans, job runs long and you eat the
days. Little compartmented bathroom with a damp corner? Fans everywhere, and now you are explaining an
equipment bill you cannot defend. The paper's own words for the two failure modes are underutilization on some
projects and abusive overuse on others. Neither one is good for you.The area method fixes both, and it does it with a number you can actually point at.
Where 60 to 120 SF comes from, so you can say it out loud
Dri-Eaz ran the testing in the fall of 2013 and the Consensus Body put it in the paper at pages 8 and 9.They measured what area a normal restoration air mover actually covers at a given air speed. At 600 FPM or
better, one air mover covers 60 to 120 SF of wet surface. That is the range this calculator sizes to, and it
is the wet part of the job, when there is still free liquid water in and on the material.One catch you should know about before somebody else tells you. Those numbers came off smooth, unobstructed
concrete. The paper calls them the absolute maximum potential coverage. Your actual job has furniture, corners,
toe kicks, and a sectional nobody wants to move. On a cluttered or complicated space, expect to land at the
heavy end of the range rather than the light end.And this is not fan-company marketing. The paper backs the velocity ranges with five peer-reviewed sources,
Lamb, Steiner, Simpson, Mujumdar and Perry, all landing in the same neighborhood: roughly 200 to 600 FPM is the
useful range, you stop getting much benefit past 400 to 600, and below about 100 to 250 the drying rate starts
to suffer. Blowing harder is not a strategy. Covering the wet surface is.
What class is really doing here
Class does not change the math. It changes what you feed the math. The whole point of the area method isthat the count follows wet surface, so class just tells you which surfaces to count. That is why class sits at
the top as one setting instead of living in every row.
- Class 1. Least water. Part of a floor, not much wicking up the wall.
- Class 2. More water, wicking up the walls but staying low.
- Class 3. It came from overhead. Floor, walls and ceiling are all in play.
- Class 4. Deeply held water in stuff that does not want to give it up. Concrete, plaster,
hardwood, masonry.
around between S500 editions and the white paper does not publish a class table at all. So use the preset to
get moving, then set the wet percentage and the wicking height to what you actually measured and photographed.
Six months from now when somebody asks where your number came from, “I measured it” ends the
conversation. “The software filled it in” starts a much longer one.Class 4 gets its own warning because the area method is sizing airflow for surface evaporation, and Class 4
is defined by water that is not at the surface. Once the bottleneck is moisture diffusing out from deep inside
a material, blowing more air across the face of it stops helping much. On a Class 4 the number this thing gives
you is a minimum, not a maximum allowed. Expect specialty drying, heat, and extended dry times, and expect to
document why you needed them.
Why the old 10 to 16 linear feet number is still on this page
The 2006 third edition raised air mover counts to the level of the standard of care and gave everybody aperimeter rule: one air mover for every 10 to 16 linear feet of wall, outlets all pointed the same direction,
plus consider at least one for each small bathroom, closet or other offset or inset. That is S500 third
edition 12.1.20, quoted in the white paper at page 5.It is on this page because plenty of estimates, reviewers and software presets still run on it, and sooner
or later you will be on the phone explaining why your number and their number are different. When the two
counts diverge hard, that divergence is usually the whole story: a big open room where the perimeter method
starves the middle of the floor, or a chopped up little space where it piles on fans nobody needed. Being able
to show both numbers and explain the gap is worth more than being right quietly.The offset and inset allowance carried forward into this calculator as its own input, because that part of
the old guidance was correct. Air does not turn corners by itself.
Who made this
Know the number. Know where it came from.
I am Andrew McCabe. I work property damage claims from the insurance side and I do expert witness work for plaintiff's attorneys, which mostly means I get hired after the fight over equipment days has already started. This calculator exists because I keep reading mitigation files where the drying was fine and the documentation was not.If you own a restoration company and you are tired of defending your invoice line by line, that is the thing I work on with people. Same idea as this page: know the number, know where it came from, be able to say it in one sentence.Share this page with anyone who needs it.
