Differences between thermal and ULV foggers

Insect foggers can be categorized into two large categories – cold foggers or ULV foggers and thermal foggers. You may have come across one or both of these terms if browsing insect fogger products. While the purpose of both fogger types is the same, actually they use pretty different fogging techniques and also require different types of fogging liquids.


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 gets 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 thermal fogger heat barrel.

l, it instantly is vaporized. This allows the fogger to produce a large count of particles in extremely small size, which altogether forms a dense cloud of fog. As mentioned there are two types of thermal foggers – gas and electric. They are pretty similar when it comes to their appearance, but gas fogger uses gas (mostly propane) to preheat the heat assembly, so a gas cylinder needs to be mounted to the fogger, while electric foggers use electricity to heat the assembly, so it comes with an electrical cable that needs to be plugged into an electric outlet. Gas powered foggers are fully portable and you can use them in any place, as no electric cables are needed to operate the fogger, but electric foggers are subject to the length of the electric cable or extension cord. But gas fogger has larger operational costs, because the gas cylinder empties and needs to be changed, which will cost more than the cost of electricity an electric will consume.

A ULV fogger, in opposite to thermal fogger, is a cold fogger type, so it 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 in a tank and when fogger is operating the fogging liquid gets pumped out of the tank. The solution then gets pumped into a special nozzle that is construed in such a way to give the airflow a swirling motion. A high air pressure produced by the motor helps to spray the fogging liquid through 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. ULV foggers mostly work on electricity, which is needed to power an electrical motor. The particles size ULV fogger produce can be adjusted to output precise sized particles, which allows you 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 outdoors.

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.

Average particle sizes in microns

The heating technique thermal foggers use allows it 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 the particles the 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 vice versa. Thermal foggers have the advantage of producing particles in a 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 treetops 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, ULV foggers produce almost invisible fog and 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 you to adjust particle size, they can also be used outdoors or in greenhouses to spray the 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. One disadvantage of using ULV foggers outdoors is that they produce almost invisible fog, so it is going to be harder to control the direction of the fog.

Main website editor at InsectCop.net. Expert in mosquito foggers!


  1. Dear Karen,
    Can I use outdoor cold fogging solution ( to be mixed in water) in a sprayer(as fogging machines are very expensive) What results will I get.

    1. Hi Kalpana.
      You can use cold fogging solution in a sprayer, however there are few disadvantages when compared with cold ULV fogger which you need to be aware of:
      1) A regular sprayer cannot atomize fogging solution in such small particles as ULV fogger so it won’t cover as much area and won’t be able to penetrate smaller gaps and holes because of the larger particle size.
      2) Most cold ULV foggers have pretty powerful electric motors so they can output solution in much greater distances than hand sprayers, but this won’t be a problem if you need to fog a small area.
      Other than that, you can use a cold fogging solution in a sprayer.

      Let me know if you have any other questions.
      Regards, Karen.

      1. Dear Karen
        Thanks for the prompt reply and very helpful answer.Please let me know what is the difference in solution /contents used for outdoor cold fogging vs indoor cold fogging.

        1. Hi Kalpana.
          Glad that my previous answer was useful to you!
          As for your question, I think that the main difference between outdoor and indoors cold fogging solutions is their content. If you want to fog an indoors space chances are that it will be your home or a place where you spend a lot of time so you should look for a solution that is more natural and isn’t as potent, because it will be safer for you as well as it will be easier to air out the space after fogging. A good option is Pyrethin based solution diluted with water.
          But for an outdoors space a solution you can either simply use a Pyrethrin based solution, because it is natural enough so that you can spend time in the sprayed area soon after fogging but it will still kill all of the mosquitoes, or really any other solution that is meant for cold fogging in outdoors environment, because outside you don’t have to worry too much about residue or airing out the space.
          Hope this helps!

          Regards, Karen.

          1. I am looking to use a fogger to help control or get rid of bird mites in my home. I am looking at Kleen Green Natural Enzyme as it is not toxic. Spraying the entire house using a hand spray bottle is not practical. However, the Kleen Green is only effective while wet and leaves no residual effect. Would it come out of the fogger wet enough to help? I would appreciate some advise in this. Would using a humidifier be a better solution? I would rather use a fogger if this would work. Thank you.

          2. Hi Jane,
            I agree that spraying the whole house with the Kleen Green Natural Enzyme using a hand sprayer bottle isn’t practical, however, since the label says that the product needs to be applied wet and then wiped off, I am not sure that using a fogger would be your best course of action. I would suggest getting a manual pump sprayer, like this one for example, that will still distribute the product wet, but at higher rates than regular spray bottles, so it will be much easier for you to spray your whole house with the product in small amount of time.

  2. I’ve been researching thermal foggers for use around my home this spring and summer for mosquitos, biting gnats and biting flies. I live on about 30 acres surrounded partially by a swamp. I anticipate fogging about a 5 to 10 acre area with the fogger on the back of a utility vehicle. I will be fogging around my home and a three acre pond that I occasionally fish and we eat the fish. So I need something efficient and environmentally safe. I am looking at several models/brands in the 2-3 thousand dollar range(hopefully 2).

    Any suggestions would be helpful. Would you suggest water or oil based for the pond? What size should be adequate? Is there a particular brand/company that stands out? thanks

    1. Hello.
      First of all, lets start with the pond. In general, there is no difference whether you use a water or oil based product when it comes to fish, what matters is the active substance used in the solution, some of these substances can be very harmful to fish while others are less. The important thing is to always read the label and gather as much information as possible of the insecticide your are going to use. In general, insecticides advertised as bio or natural are going to be less harmful to fish.

      Another thing when comparing oil and water based solutions is that oil insecticides are going to provide a longer effect, because they last for much longer time on the fogged surface than water based solutions, which is great for mosquito control. Oil based solutions can also be applied in more windy conditions.

      However, when we consider safety of the environment, water based products are better because they evaporate faster, which, for example, is better for fish, because they stay in contact with the chemical for much less time.

      When talking about foggers there are few great options available, ones that can output water based solutions, oil based, or even both. You have done a good research to choose thermal foggers, because practically all of them can output particles at 5-30 micron size, which is the most effective for insect control. From companies, I would suggest either VectorFog or Curtis Dyna-Fog, both of these make highest quality thermal foggers for large area fogging.

      From foggers that can output oil based solutions I can recommend this:
      Golden Eagle fogger by Curtis Dyna-Fog -> http://amzn.to/1LDHQtz

      And there are also some high quality foggers that can output water and oil based solutions such as:

      Regards, Karen.

  3. Ratio of cedarwood oil and hydrated silica use in fogger machine to rid off from mold. Can I use thermal fogger to make fog of cedarwood oil and hydrated silica or cedarwood oil and ethyl lactate. Pls suggest.

    Your advice will help to make one house mold free.

    1. Hi Vicky,
      Well it depends on what type of solution you are using.
      If you are referring to a store bought product like the Wondercide Natural Indoor Pest Control Spray for example then you should check the label of that products and see what it says, since it should be stated there what type of application this product is suitable for (in the case of the previously mentioned Wondercide spray, the label of it clearly says that it is suitable for spray or fog application).
      But if you are mixing the ingredients yourself, then you need to see if your fogger is suitable for them. As long as your fogger can be used with oil based solutions, since you are mixing cedarwood oil with other ingredients, it should be fine to use the solution with you fogger machine to make your house mold free.
      If you have any more questions, don’t hesitate to use the contact form on the website to contact me directly!

      Hope this helps!

  4. Hello, quite interesting questions and answers, i’m to work on a vessel (ship) and also industrial office spaces. I am buying ULV Cold fog for the vessels/plateform and a thermal fog machine for out door uses. I reside in tropical countries (Nigeria, Africa).
    1. can this machines serve pest cointrol in this region
    2. can the solution used for thermal fog machine be used for the ULV COLD FOG
    3. If i am to used a ULV COLD FOG what is the solution quantity i will use to fumigate a building of 30m*30m and the height is 15m

    1. Hi Paul,
      To answer your questions:
      1. Both the ULV and the thermal fogger will be useful for pest control, especially in tropical countries. You just have to make sure that you get a fogging solution, that is suited for the pests that you want to combat.
      2. It depends on what solution it is. There are some that can be used with both and some that are suited for only one type of fogger. I would recommend to check the label of the solution (on the solution bottle or on the Internet) and see what type of fogging machines it is suitable for, since that information should be mentioned somewhere.
      3. Again, it depends on the solution and this information should be mentioned on the label or in the user guide if it has one. If not then I would say a gallon of solution should be enough for a 30 by 30 meter since the space isn’t that large, especially if it is an indoors space. Just remember to also check if the solution you buy can be used indoors, since there are some that can only be sprayed outdoors.

      If you have any more questions, don’t hesitate to use our contact form on our Contact Us page, to contact me directly.

  5. Hi karen
    It is very knowledgeable questions and answers done by you. I have one little question, that what is the quantity of insecticides in ulv fogger sprayer in outdoor if I used 500ml of any Insectiside in 200 litter of water for one acre of land by knapsack sprayer, if I using ulv sprayer it consume only 20 litter of water for one acre. So what is the quantity of insecticides for ulv fogger .

    1. It depends on the insecticide you are using. Instructions and the insecticide to water proportions should be noted on the label of the insecticide.

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