Water Only Fog Machine
Everybody loves fog, Theatrical Fog that is - Especially at Halloween, and there are many ways to make it:
1. Dry Ice was my first introduction to fog - Dry Ice dropped into hot water provided LOTS of dense low-lying fog. It was great, but you had to go get the dry ice and be very careful handling it. When I lived in San Jose, California there was a company called Able Carbonic near the airport that had a Dry Ice Drive Through around Halloween - it was great!. You could pull your car right into their warehouse and purchase however much dry ice you wanted without leaving your car.I've built a couple of contraptions to make using dry ice fog easier.
A safety note - Dry Ice is Carbon Dioxide and in addition to being extremely cold (-109.3°F or -78.5°C), causing instant cold 'burns' on contact (use insulated gloves), it can present a suffocation hazard because the carbon dioxide gas evaporating off of it will displace the normal air around you and deprive you of oxygen. I once had a small room filled with dry ice fog and it became apparent by the coughing and faster breathing that there was too much carbon dioxide in the room - Exit NOW if you find yourself in such circumstances!
2. Heated 'Fog Machines' that heat glycol-based or glycerin-based 'Fog Juice' to spray out a plume of white smoke/fog. I like to think of these as smoke machines more than fog machines. These are used at concerts to make the beams of light/lasers show up, and traditional low lying fog too . My commercial photographer friend introduced me to this type of 'fog' machine. He had a professional Rosco unit that was really built like a tank and pumped out tons of smoke. I eventually purchased a Rosco unit and have since purchased consumer 'fog machines' of various sizes at big box retailers on clearance after Halloween so that now I have 3 (or more, not really sure how many I have ;-).
'Fog Machine' fog tends to disperse all around you as if in a London Fog, so if you want it to hang near the ground you have to chill it. There are tons of Insturctables how to build one of these fog chillers.
3. Here is the new fog method - Ultrasonic Atomization. This is where a piezoelectric disk is electrically pulsed to vibrate at ultrasonic frequencies with a shallow layer of water over it. The surface of the water breaks up into fine droplets; fog. Ultrasonic humidifiers use this method to produce the visible mist being blown out of them. Many years ago I saw the fog potential of ultrasonic humidifiers and 'plumbed' the output of one of them via a hose into a jack-o-lantern to have fog creeping out of its mouth.
Fast forward to today. You can get high capacity pond foggers that will produce large amounts of fog (using >2 liters of water an hour). These high output atomizers are not cheap (~$200) but dump out tons of fog, low lying fog, without any carbon dioxide gas. No consumables but water and electricity!