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Fog Machines heat propylene glycol to create fog. The heating of the fog juice has the drawback that warm fog tends to rise. Warm fog also tends to dissipate or float away quickly. To combat the problem of fly away fog, it can be chilled. Chilling the fog keeps it from rising immediately, instead it hugs the ground. The ground hugging fog also has a little more creepy feel than a cloud of smoke, which is sometimes more desirable. Also, a low fog tends to hang around longer.
The concept is easy, connect the output of a fog machine to a device to remove heat from the fog as it flows past. A simple way to achieve this is to adapt a ice chest or trash can. The fog enters the ice chest full of ice, cools down and comes out the other side nice and cool.
The first consideration is that the output nozzle on a fog machine is very hot. The connection made to the fog machine must ensure that no direct contact is made with the nozzle. The next consideration is that the pressure of the fog coming out of the fog machine is limited. If you try to run the fog through too much pipe or around too many bends, the pressure will be lost and it won't make it all the way to the output hose. The final consideration is that the more contact with ice the smoke makes, the more effective the fog chiller will be.
Many designs for fog chillers exist, some use ice chests, some use trash cans, some involve recirculating water through a coil. You could even use a cardboard box if with the right design. Avoid using a container that is too small. The fog needs room for initial expansion and room for lots of ice surface contact. A small space can cause the fog juice to recondense and yield disappointing results.
For our design, we like a plastic trash can. Some people think the ice chest is best because it keeps the ice insulated, but you are running hot fog over the ice, that melts it much faster than anything else. Any size trash can you want to use is fine to suit your purposes, but it needs to big large enough to coil the hose inside and still have room for ice.
We used a 30 gallon plastic trash can and cut a four inch diameter hole in the side, a couple inches up from the bottom. Next we inserted a short piece of rigid 4" dryer ducting through the hole and bent down the fins to secure it in place. Inside the can we placed a 4" ducting band clamp over a 15 foot section of flexible aluminum dryer ducting and connected the ducting to the rigid duct through the side of the trash can. We tightened down the band clamp to secure the ducting in place. We then repeated this process just under the top rim, on the opposite side from the top opening (although this was to suit our layout, you can place the hole anywhere to suit your needs).