HOW TO MAKE FOG For each 15-minute period put 5 to 10 pounds of Dry Ice into 4 to 8 gallons of hot water. This will make lots of fog depending upon the temperature of the water and the size of the pieces of Dry Ice. Hotter water will make more fog. Very hot water will add its own rising steam to the vapor cloud. If there is no steam the fog will flow down hill and in the direction of any air movement. A small fan can help control the direction. Smaller pieces of Dry Ice with more surface area produce a greater volume of fog and cool the water down much faster. In both cases the result is more fog for a shorter amount of time. Keep the water hot with a hot plate, electric skillet, or some other heat source to produce fog for a longer time. Otherwise when the water gets too cold it must be replaced to continue the fog effects. If the container is completely filled with water the fog will flow over the sides the best. But the Dry Ice sublimation will vigorously bubble the water and splash it out. Even a ¾ filled container will splash some so place the container where spilled water will not ruin anything. The water vapor fog will also dampen the area it flows across. Be careful because after some time floors do get slippery.