Why 15-30 Microns Is the Most Important Number on a Disinfection Sprayer's Spec Sheet in 2026
Last updated: 6 Sep 2026 | 3 Views |
Understanding droplet size in 2026
Why 15-30 Microns Is the Most Important Number on a Disinfection Sprayer's Spec Sheet in 2026
The one number that decides whether mist fills the room, falls within a metre, or simply drifts away.
A disinfection sprayer's spec sheet has dozens of numbers on it, but only one decides whether the machine solves your problem or simply makes things wet: droplet size. Here is why the 15-30 micron band is the range that actually works indoors.
When people compare disinfection sprayers, what gets discussed is usually tank size, wattage and price. Droplet size is often overlooked, or not stated at all — even though it is the number that most determines the outcome.
The reason is simple. Droplet size determines how far the disinfectant travels. Too large and it falls before reaching the target. Too small and it drifts away without doing any work. The right band is the one that carries solution to every point in the room and then settles evenly.
This article explains why the 15-30 micron band is the working range, and how to test for yourself whether the machine you have or are about to buy is really in it. Our reference machine is the AIROFOG U260: a German-engineered ULV cold fogger with an 800-watt motor, an adjustable nozzle, and 15-30 micron droplets.
The story
Three machines in the same room, three completely different results
Picture a sixty-square-metre meeting room with a three-metre ceiling, a long table, twenty chairs, a ceiling-mounted projector and two air vents. Now fog it with three different machines.
The first produces droplets below ten microns. They are so light they rise and get carried out through the return vent by the air conditioning before settling on anything. The room looks beautifully misty and most surfaces receive almost no solution.
The second produces droplets above fifty microns. They are heavy enough to fall to the floor within a metre of the nozzle. The floor along your walking route is wet, but the ceiling, the vents and the corners get nothing — and you have to wipe the floor afterwards.
The third produces droplets in the 15-30 micron band. They stay airborne long enough to spread through the room, reach the ceiling and the vents, and then settle across every surface as a thin film that dries by itself within minutes.
Why below 10 microns is not as good as it sounds
Many people assume smaller is always better, because it sounds as if finer mist reaches every corner. That is only half true.
Very small droplets weigh so little that gravity has almost no effect on them. They drift with the airflow from air conditioning and fans, and in a room with the air conditioning running, a portion is drawn into the return vent and leaves the space before doing any work.
Very small droplets also evaporate faster. In Thailand's hot, relatively dry conditions, the water in a droplet can evaporate before the droplet reaches a surface, meaning less solution actually lands than it should.
This is why choosing a machine by looking for the smallest droplets is the wrong approach. The goal is not to produce visible fog; it is to get solution onto real surfaces.
Why above 50 microns becomes spraying water
Conversely, droplets above fifty microns are heavy enough that gravity quickly overcomes air resistance. They travel in a downward arc, exactly like water leaving a spray nozzle.
In practice that means most of the output lands on the floor within a metre of the nozzle. Anything above waist height receives almost nothing, and the ceiling and air vents — the hardest places to reach — receive nothing at all.
The side effect is damage: damp carpet, wet paperwork, slippery floors and water sitting on electrical equipment. This is the main reason many organisations abandon a sprayer after only a few uses.
High-pressure agricultural sprayers sit in this group. That does not make them bad machines; they are excellent for what they were designed for — applying product to leaves in a field, where you want the droplets to land quickly on target and not drift.
The 15-30 micron band is where both conditions are met
In the 15-30 micron band, droplets are light enough to stay airborne long enough to spread through the room's volume and reach surfaces above head height, and heavy enough to eventually settle rather than drifting away.
In practice this is what gives a properly fogged room three characteristics at once: floors dry within minutes, items on desks are not wet, and the ceiling corners genuinely receive solution.
It is also why an adjustable nozzle matters more than tank size. Even within the band, setting it towards fifteen microns suits rooms with electrical equipment and paperwork, while setting it towards thirty suits bathrooms and tiled floors.
A machine that states this band on its spec sheet and offers an adjustable nozzle can therefore serve every zone in a building from a single unit.
What it actually costs
Choose droplets too small and the solution never reaches surfaces
Below ten microns, droplets drift with the airflow and can be drawn into the air conditioning return before settling. The room looks misty while surfaces receive less than they should.
Choose droplets too large and you get damage instead of results
Above fifty microns, droplets land within a metre: damp carpet, wet paperwork, slippery floors — while the ceiling and vents receive nothing at all.
A spec sheet with no droplet size tells you nothing
Many machines on the market state only wattage, tank size and output in litres per hour, with no droplet size at all — leaving the buyer no way to know how the machine will behave in their room.
A machine that damages things gets abandoned within a few uses
Most organisations that stop using a sprayer do not stop because it broke. They stop because the first use damaged documents or equipment and nobody dared use it again.
Why the usual fixes fail
Looking at output in litres per hour instead of droplet size
Output rate tells you how much solution leaves the machine per unit of time, not where that solution goes. A machine with high output and large droplets simply wets the floor faster.
Assuming smaller droplets are always better
Droplets that are too small drift out of the space and evaporate quickly in hot air, so less solution reaches surfaces. The goal is solution landing on surfaces, not attractive-looking fog.
Judging by how much fog you can see in the room
Visible fog density does not tell you whether solution reached the ceiling. A room full of thick visible fog may simply be one where large droplets are on their way to the floor.
Using an agricultural machine indoors because it is more powerful
Agricultural machines are designed to land droplets on target fast and not drift — the opposite of what a building needs. More power does not help; it just produces damage faster.
Buying a machine with a fixed nozzle because it is cheaper
One building contains both rooms full of computers and tiled bathrooms. A fixed nozzle suits one or the other, and you will end up buying a second machine anyway.
How to test for yourself whether a machine is in the right band
You do not need laboratory droplet-sizing equipment, because droplet behaviour in the correct band is observable with the naked eye in ordinary use. There is a simple three-part test.
First, after a pass the floor should be dry within minutes and not slippery. If there are puddles or you have to wipe afterwards, the droplets are too large.
Second, items on desks — paperwork, keyboards — should show no water marks. Third, the ceiling corners and air vents should genuinely have received solution, visible as a faint film while still drying, or verified with indicator paper placed before the pass. If all three pass together, your machine is working in the right band.
10 reasons the AIROFOG U260 solves it
1. 15-30 microns is the balance point between drifting and settling
Light enough to spread through the room's volume and reach the ceiling, heavy enough to eventually settle on surfaces. Both conditions have to be met at once for the treatment to work.
2. Floors dry fast enough to use the space again immediately
The thin film droplets in this band leave dries by itself within minutes, which is the condition that makes fogging between uses genuinely possible in schools, clinics, shops and offices.
3. It lets you fog rooms containing electrical equipment
Droplets in this band set towards the drier end leave no water sitting on equipment, so server rooms, computer rooms and counters with tills can be treated — something large-droplet machines cannot do.
4. It reaches ceilings and vents that nobody ever wipes
In almost every building, the surfaces that never get cleaned are the ceiling and the air vents. Droplets in this band rise to reach them and settle there, which is the main reason fogging differs from wiping.
5. Floors are not slippery, which matters where people walk
A thin film is not a puddle, so floors are not slippery — a necessary condition for care homes, hospitals, shops and public buildings with elderly people walking through.
6. It uses far less solution than spraying
Because the mist distributes through the volume rather than pooling in one place, the amount of solution used per area is significantly lower than spraying, which cuts the cost per pass considerably.
7. It works fast enough to be done routinely
The speed at which this band covers a space means a sixty to ninety square metre room takes only a few minutes — the condition that turns fogging into a daily routine rather than a monthly event.
8. It can be adjusted within the band for each zone
Set towards fifteen microns for rooms with equipment, towards thirty for bathrooms and tiled floors. A machine that adjusts serves a whole building from one unit.
9. It works with a wide range of disinfectants
A machine working in this band is a delivery system, not a lock-in to one chemical brand. You can use the product your organisation has approved, and change it later without changing machines.
10. It is a verifiable specification you can cite in documentation
When an organisation has to submit documentation to a customer, an inspector or a supervising authority, stating a clear droplet size carries weight — unlike simply writing that a disinfection sprayer was used.
Before and after
Before
- Comparing machines on wattage, tank size and price, with no attention to droplet size
- Believing that smaller droplets are always better, or that more output is always better
- Using large-droplet machines indoors: damp carpet, wet paperwork, slippery floors
- Ceilings and air vents never receiving any solution despite every pass
- Having to wipe the floor after every pass, until fogging became a burden
- Abandoning the machine within a few uses because it damaged things
After
- Choosing a machine with droplet size as the first specification checked
- Using the 15-30 micron band, which fills the room and settles as a thin film
- Floors dry within minutes and not slippery, so the space is usable immediately
- Paperwork and electrical equipment undamaged, so rooms with contents can be fogged
- Ceilings and air vents genuinely treated on every pass
- A few minutes per room, so fogging became a daily routine
How we get you started, in 3 steps
1. Check the droplet size specification before anything else
Before looking at price or tank size, check whether the specification states a droplet size at all, and what band it gives. If it is not stated, that is a signal you have no way to know how the machine will behave in your room.
2. Run the three-part test in your own space
After a pass, the floor should be dry within minutes and not slippery, items on desks should show no water marks, and the ceiling corners and vents should genuinely have received solution — verifiable with indicator paper placed before the pass. Pass all three and your machine is in the right band.
3. Have us set the nozzle for each of your zones
Being in the right band is a property of the machine; being set correctly for each zone is a property of the installation. We set the nozzle towards the drier end for equipment zones and normal for tiled zones, work out the dilution, and train your team.
What a customer says
“When I bought my first machine I only looked at wattage and tank size. It was only in real use that I learned the most important number is droplet size, because it decides whether the solution reaches the ceiling or lands on the floor in front of you. These days when somebody asks me what machine to buy, my first question back is whether the spec sheet states a droplet size at all.”
Facilities manager — An organisation using ULV fogging daily
What a micron is, and why a few microns changes everything
A micron is one millionth of a metre, or one thousandth of a millimetre. A human hair is about seventy microns thick, so a thirty-micron droplet is about half the thickness of a hair.
The reason a few microns changes droplet behaviour so completely is that a droplet's weight increases with its volume, which scales as the cube of its size, while air resistance increases with its cross-sectional area, which scales as the square.
So when droplet size doubles, weight increases eightfold while air resistance increases only fourfold. Droplets therefore fall far faster than the size ratio alone would suggest.
That is the physical reason why a thirty-micron droplet and a sixty-micron droplet behave like completely different things, even though the numbers look only twice apart.
Why Thailand's climate makes this band matter even more
In hot, relatively dry air, small droplets evaporate faster than they would in cool, humid air — which means droplets that are too small can evaporate entirely before reaching a surface.
Conversely, air-conditioned rooms in Thailand are usually set cold with strong circulation, so very light droplets are carried along with the airflow and can be drawn into the return vent before doing any work.
The 15-30 micron band therefore suits Thai operating conditions particularly well: it has enough mass not to evaporate away in hot air, and is not so light that the air conditioning removes it before it settles.
In practice this is why a machine stating this band with an adjustable nozzle works both in air-conditioned rooms and in semi-open spaces such as canteens and building lobbies — the two conditions most common in Thai buildings.
Frequently asked questions
What droplet size suits indoor work?
The 15-30 micron band: light enough to spread through a room and reach the ceiling, heavy enough to settle as a thin, fast-drying film.
Why are droplets below 10 microns not better?
Because they are too light: they drift with the airflow and can be drawn into the air conditioning return before settling, and in Thailand's hot air they evaporate quickly, so less solution reaches surfaces.
Why can droplets above 50 microns not be used indoors?
Because they land within about a metre, wetting floors and making them slippery, damaging paperwork and equipment, while ceilings and vents receive nothing at all.
What if the specification does not state a droplet size?
Ask the seller directly and request the manufacturer's specification sheet. If that information does not exist, assume you have no way to know how the machine will behave in your room — a risk not worth taking.
Can I test for myself whether a machine is in the right band?
Yes. Use the three-part test: after a pass the floor should be dry within minutes and not slippery, items on desks should show no water marks, and the ceiling corners should genuinely have received solution — verifiable with indicator paper placed beforehand.
What does an adjustable nozzle add if the machine is already in the band?
Even within the band, setting towards fifteen microns suits rooms with electrical equipment and paperwork, while setting towards thirty suits bathrooms and tiled floors. One adjustable machine serves a whole building.
Does droplet size affect how much solution I use?
Considerably. Droplets in the correct band distribute through the volume instead of pooling in one place, so they use significantly less solution per area than spraying, which reduces the cost per pass.
Can droplet size be cited in reporting documentation?
Yes, and it should be. Stating a clear droplet size gives documentation submitted to customers, inspectors or supervising authorities far more weight than simply writing that a disinfection sprayer was used.
If you can only check one number on the spec sheet, check droplet size
Of all the numbers on a disinfection sprayer's specification, droplet size is the one that decides whether solution reaches the ceiling, lands on the floor in front of you, or drifts away without doing any work.
The 15-30 micron band is what makes three things true at once: floors dry fast, nothing is damaged, and ceilings and vents genuinely receive solution — the three conditions that decide whether fogging becomes routine or gets abandoned.
If you are choosing a machine, or want to know where the one you already own sits, send us its specification and your building layout and we will tell you which of your zones it suits.
See the AIROFOG U260 ULV cold fogger, specifications, droplet range and price
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