A Not-So Chilling Tale Of Halloween Fog

The past few years our annual Halloween display included fog effects augmented by the use of “chillers” to cool the output of the fog machines. This year we tried a new design for fog chillers. This is a little report on the differences, and why the new design was something of a disappointment.

The process of making artificial fog using a water & glycerine solution involves using heat to transform the solution into a vapor. The fact that its warm makes the fog tend to rise…which is exactly what you don’t want for spooky fog-creeping-along-the-ground-effects.

A few years ago we found a design for a fog chiller that was based around a common ice chest. The principle was simple enough, use some common PVC plumbing fittings to turn a cheap cooling chest into a chamber that could be filled with ice. Then blow the fog through that chamber hopefully cooling it enough so that when emerges on the other side it creeps along the ground.

Our first pass at these fog chillers worked, but not very well. The trouble was two-fold; the fog passed only a short distance through the cooler in contact with the ice, so it wasn’t cooled dramatically. Further, the ice kept melting and he to be replenished frequently.

The following year we enhanced the chillers by creating a more complex path through the cooler. The longer path for the fog made the a bit more effective at cooling.

The greatest improvement we found by switching from standard ice to dry ice. Dry ice is somewhat hazardous to handle but is so very cold that it dramatically cooled the fog, and resulted in some outstanding creepy fog.

The problem with dry ice is that it’s more difficult to procure. Supermarkets carry it but only in limited qualities. If Halloween is a popular event in your area you may find that their supply gets bought up by people throwing parties. Also, it costs about $2 a pound, and we found that we could use around 30-50 pounds for the night…so there’s a cost consideration, too.

This year Stella found a promising looking new approach to fog chillers. Instead of using coolers it was based upon 30 gallon plastic trash cans. Then the author used aluminum dryer vent hose to create a 24 foot spiral path for the fog, from the top to the bottom of the can.  He then back filled the trash can with normal ice.

Since the cost of the supplies to make a couple of these was going to be about the same as the cost of dry ice for the night I decided to give them a try. It also helped that one of our neighbors has an industrial ice machine. He would happily provide up to 500 pounds of ice for free, I just had to move it down the street.

It happens that two wheel barrow loads of ice filled both our fog chillers with a little left for spare. I’m guessing that it was around 250 pounds of ice.

The fog effects throughout the evening were just ok…not outstanding…but adequate. The fog machines were on auto timers so they cycled on/off on their own. The picture above catches a moment when the fog was not especially dense.

We also had some wind that evening, which tends to cause the fog to blow away fairly quickly. Usually as the evening goes on the wind drops away, so later in the night the fog effects are generally better.

When we finally ran out of candy around 9pm I checked one of the fog chillers and was surprised to find that it was still very full of ice. It would be long into the next morning before it would melt away.

The lesson from all of this I realized while looking at a freezer full of dry ice at a supermarket. There was a sign that declared, “Dry ice has five time the cooling power of normal ice.” That seems about right. Our new fog chillers held about 4-5 times the normal ice that our older, smaller coolers could hold. Thus the newer and much larger fog chillers were nearly as effective as the older one when we used dry ice.

I think that I’ll try an entirely new approach next year, because I want something that’s dramatically more effective than anything we’ve achieved to date.