Thermal vs. ULV (Cold) Foggers Diffrence - 7stories®
Thermal vs. ULV (Cold) Foggers
Thermal foggers, as the name suggests, use heat in the fogging process. Thermal foggers use heat to vaporize a fogging solution and spray it out in form of a fog. Thermal foggers are equipped with a heat barrel that is preheated to high temperatures using either a propane gas or electricity depending on the type of a fogger. The fogging solution is in a liquid form, and when it gets pumped into the heat barrel, it instantly is vaporized. This allows the fogger to produce large count of particles in extremely small size, which all together forms a dense cloud of fog. 

An ULV fogger operates using cold fogging techniques. To produce fog into small droplets foggers are equipped with motors that produce a high power, low pressure air stream. Same as with thermal foggers, the fogging solution is stored into a tank and when fogger is operating the fogging liquid gets pumped out of the tank. Solution then gets pumped into a special nozzle that is construed in such a way to give the air flow a swirling motion. A high air pressure produced by the motor helps to spray the fogging liquid trough the nozzle separating it into tiny particles. The liquid solution gets sprayed out of the nozzle in form of a fog or a fine mist. The particles size ULV fogger produce can be adjusted to output a precise sized particles, which allows to use the fogger in different applications. Also, because ULV foggers use cold fogging techniques and do not get heated to high temperatures, they can be used both indoors and outdoor
Particle sizes
The particle size produced by thermal and cold foggers will vary based on the model of the fogger. However, thermal foggers generally will produce smaller in size particles, averaging from 0.5-10 micron range, while ULV foggers will output a bit larger in size particles, averaging from 5-30 micron range.The heating technique thermal foggers use allows to produce extremely tiny particles, as small as 0.5 microns, which can penetrate very small areas indoors and outdoors. Insecticide or other solution is vaporized to produce a dense and thick cloud of fog. The fog produced by a thermal fogger is easily visible, which allows to better control the direction of the fog. Different ULV foggers will produce different sized droplets, based on the use of the fogger. While thermal fogger can produce extremely small particles, their size is inconsistent meaning that particles a fogger outputs will range dramatically from 0.5 up to 30 microns in size. ULV foggers at the same time can produce a very consistent particle size and particle size of these foggers can be adjusted by adjusting the flow rate. This is especially useful if you need to fog different areas or use the fogger for various purposes, for example getting rid of molds or unpleasant odors indoors or killing insects and other pests outdoors. ULV foggers also need less diluent, so they can produce more concentrated fogging solutions, which make some type of chemicals cheaper to use.

The usage of both thermal and ULV foggers is similar in many ways, as both devices are generally foggers or misters and are used to spray out either a water or oil based fogging solutions. Both types of foggers are used in such applications as insect control, odor and mold control in indoor areas, for disinfection, to apply pesticides to plants, getting rid of pests in warehouses and other similar uses. Besides these places, there are other areas, where thermal foggers are better suited than ULV foggers and other way. Thermal foggers have advantage of producing particles in smaller size than ULV foggers and the fog is also easily visible, which makes them better in such applications as:

Mosquito and insect control. Because of small droplets a thermal fogger produce, they are good for mosquito and other smaller insect control. For mosquito control the best droplet size is from 5-20 microns, and most thermal foggers will produce particles in this range. Controlled outdoor fogging. Because fog that a thermal fogger produce is thick and easily visible, you can more easily control the direction of fogging. This will make an outdoor fogging more controlled, because most ULV fogging devices produce hardly visible fog.
Fogging obstructed areas. Because of small particle size, fog produced by a thermal fogger can reach in very small places such as floor gaps, cracks in walls and similar places indoors, or into thick bushes, long grass, high tree tops and other hard to reach outdoor places. ULV foggers in opposite do not use extensive heat in fogging process, so they can be used indoors without fire risks. Also,  allow to adjust particle size, so they can be used in more applications than thermal foggers. ULV foggers are used:

In any indoor place. As mentioned above, ULV foggers use cold fogging techniques, so they are safe to use indoors.
For odor control and disinfection. ULV foggers are often used to disinfectant houses and large warehouses as well as control unpleasant odors in such areas. ULV fogger can be left to work automatically and there isn’t need for a person to operate the fogger all the time as with thermal foggers.To get rid of molds. ULV foggers are also used with special chemicals to get rid of molds in indoor areas. On plants and greenhouses. Because ULV foggers allow to adjust particle size, they can also be used outdoors or in greenhouses to spray different solution on plants.
Indoor and outdoor pest control. ULV foggers are the best pest control method for indoor areas, however, they are also used outdoors, for example to control mosquitoes. Although ULV foggers cannot produce such small particles as thermal foggers, some ULV foggers can produce particles from 5-20 micron range, which is effective for mosquito control.