Thermal fogger vs cold (ULV) fogger: which dry-fog machine to choose?
Thermal foggers make dense, visible fog; cold ULV foggers are safer indoors. Compare the two technologies and pick the right dry fog unit.
If you are choosing a dry fog unit for car interiors or room odour treatment, the decision usually comes down to two technologies: the thermal fogger and the cold (ULV) fogger. Both create dry fog, but they generate it in very different ways.
Short answer: a thermal fogger heats the liquid until it vaporises and then condenses into a dense, highly visible fog of roughly 10µm droplets with excellent penetration — but it produces heat and a little exhaust, so you ventilate afterwards and don't stay inside. A cold fogger uses air pressure with no heat to atomise the liquid into 5–30µm droplets, making it safer for enclosed indoor use, though the fog is thinner and less visible. In both cases this new technology relies on the same glycol-based dry fog that behaves like a gas.
What is dry fog and how does it remove odour?
Dry fog is an ultra-fine aerosol of 5–20µm droplets. Unlike the wet mist from a sprayer or steamer, it does not leave surfaces damp. Because the droplets are so small, the fog stays airborne for minutes and behaves like a gas: it penetrates the ventilation system, A/C ducts, fabrics, carpet backing and the gaps between seats.
There it binds odour molecules at their source instead of masking them. The result:
- no moisture, streaks or residue
- reaches places a cloth or spray bottle cannot
- works against smoke, mould, pet and food odours
A typical treatment runs 45–60 seconds of fogging, followed by 15–20 minutes sealed so the aerosol can settle everywhere.
How is dry fog different from wet spraying?
A regular sprayer or steamer produces larger, wet droplets that fall quickly onto surfaces and leave moisture and streaks. Dry fog droplets are tens of times smaller, so they:
- stay airborne and fill the space evenly
- penetrate hidden cavities and ducts
- dry without a trace, without damaging the surface
That difference is exactly what makes a fogger more effective at odour removal than spraying by hand.
How does a thermal fogger work?
A thermal fogger feeds the liquid into a heated chamber, where it vaporises and condenses the moment it hits the air. This creates a very dense, visible cloud of uniform droplets around 10µm.
Strengths:
- maximum density and penetration — ideal for strong, deeply embedded odours
- the visible fog lets you check coverage by eye
- high throughput in a short time
Limitations:
- the unit heats the liquid and can give off a slight exhaust smell
- you must not stay inside during treatment; ventilate afterwards
- noise and heat are higher than with a cold fogger
How does a cold (ULV) fogger work?
A cold fogger, or ULV unit (ultra-low volume), uses air pressure and a nozzle rather than heat to create the fog. Droplet size usually falls between 5–30µm and is often adjustable.
Strengths:
- no heat and no exhaust — safer for enclosed indoor use
- generally quieter and easy to handle
- adjustable droplet size for different jobs
Limitations:
- the fog is thinner and less visible, so visual control is harder
- for very deeply embedded odours it can fall short of dense thermal fog
Thermal fogger vs cold fogger: comparison table
| Feature | Thermal fogger | Cold / ULV fogger |
|---|---|---|
| Method | heats liquid (vaporise + condense) | air pressure, no heat |
| Droplet size | uniform ~10µm | 5–30µm, adjustable |
| Fog density | very dense, visible | thinner, less visible |
| Indoor safety | ventilate after, don't stay inside | better for sealed rooms |
| Best use | strong, deep odours, high volume | sensitive spaces, frequent use |
| Noise / heat | higher | lower |
Which one should you choose for a car interior?
For car-interior odour treatment both technologies are used — the choice depends on throughput, indoor constraints and budget:
- A thermal fogger suits you if you treat many cars in a row or fight very strong odours and can ventilate afterwards.
- A cold fogger suits you if you work in enclosed spaces, want quieter operation and frequent use without exhaust smell.
Self-service terminals typically use a thermal-type generator, because it delivers a fast, visible and powerful result with minimal manual work.
How to make the final choice?
Weigh four factors: throughput (how many jobs per day), indoor constraints (can you ventilate), tolerance for noise and heat, and budget. Both foggers leave a residue-free, lasting result with no moisture or streaks — the difference is in the workflow, not the quality of the outcome.
Frequently asked questions
Does dry fog leave marks or moisture? No. Correctly dosed dry fog leaves no moisture, streaks or residue — the droplets are too small to wet surfaces.
How long does a treatment take? Fogging takes 45–60 seconds, after which the space stays sealed for 15–20 minutes.
Can I sit in the car during thermal fogging? No. A thermal fogger gives off heat and a little exhaust, so you should leave the space and ventilate afterwards.