How to Make a Fog Machine for Halloween: Chillers and Dry Ice

Updated September 2026 · Home Project Resources

If you want to know how to make a fog machine for Halloween that produces the thick, low fog you see creeping across a graveyard in the movies, the secret is cold. A store-bought fogger makes hot fog, and hot fog rises and drifts away. Push that same fog through a cooler packed with ice and it comes out heavier than the air around it, so it hugs the ground and rolls. The other route is dry ice dropped into hot water, which makes a dense, bright white fog with no fogger at all, but it comes with real safety rules that you have to follow every time.

This guide covers building a cooler chiller around a fogger, a larger trash can chiller, the dry ice and hot water method, choosing fog fluid, placing fog so the wind works for you, and the safety rules for dry ice, slick residue, and smoke detectors.

Updated September 2026

Sizing the fog zone? Measure the graveyard, walkway, or porch you want covered with our free square footage calculator. The area tells you how many fog outlets you need, as the worked example below shows.

Dry ice safety comes first

Read this section before you buy a single pound. Dry ice is frozen carbon dioxide at about minus 109 degrees Fahrenheit, and it is the one Halloween material that can hurt someone badly in seconds.

The fog you see is not the gas that matters. Dry ice fog is water vapor condensed by the cold. The carbon dioxide itself is invisible, and it keeps collecting after the visible fog has cleared. One pound of dry ice becomes roughly 8 to 9 cubic feet of gas. In an open yard that disperses harmlessly. In a closed basement, a small room, or a car, it builds up.

Know the warning signs. Headache, dizziness, fast breathing, and confusion are signs of too much carbon dioxide. Get everyone into fresh air right away. A carbon monoxide alarm does not detect carbon dioxide, so a silent alarm tells you nothing about dry ice gas.

Transporting it home. Carry dry ice in a cooler in the trunk or cargo area, with a window cracked, and go straight home. Buy it the same day you use it, since a cooler loses a sizable share of a block every day as it turns to gas.

How the two methods compare

For most front yards the chiller is the better choice. Dry ice is a great accent at a single spot, such as a cauldron by the door, for the busiest hour of trick-or-treating.

How fogger fog becomes low-lying fog

A fogger pumps fluid into a heat exchanger that vaporizes it. The vapor hits cooler air and condenses into the fine droplets you see. Because that plume leaves the nozzle hot, it rises and thins out within a few feet.

Chilling the fog changes its density. Cold air is heavier than warm air, so fog cooled well below the outdoor temperature sinks and spreads along the ground until it warms up. That is all a chiller does: it gives the fog a long path past ice before it reaches the open air.

Some fluids are made for low-lying effects and hang lower on their own, but even those work better with a chiller. A regular fluid with a good chiller beats a special fluid with none.

How to make a fog machine for Halloween with a cooler chiller

This is the classic build, and it takes about an hour with basic tools.

Materials

Tools

A drill with a spade bit or a hole saw close to 4 inches, a jigsaw or a utility knife for cleaning up the holes, a marker, and safety glasses. Plastic chips fly when you cut cooler walls, and the foam inside the wall crumbles, so work outside over a drop cloth.

Building it

1. Cut the inlet hole. On one end of the cooler, mark a circle about 4 inches across, centered a few inches below the lid line. The fog needs to enter above the ice.
2. Cut the outlet hole. On the opposite end, mark a second circle low on the wall, about an inch above the floor of the cooler. The fog has to travel the full length of the box and drop down to leave, which gives it the most time against the ice.
3. Fit the ducts. Push a short stub of duct into the inlet hole and a longer run into the outlet hole. Seal around both with foil tape inside and out.
4. Install the shelf. Set the hardware cloth or wire shelf inside on a couple of blocks or cans so it sits about 3 inches above the floor. The ice goes on the shelf. Fog flows over, through, and under it, and meltwater drips to the floor where the drain plug can release it.
5. Load the ice. Pile ice on the shelf, leaving a clear gap right in front of the inlet so the fog is not blocked. A mix of block ice for staying power and cubes for surface area works best. Frozen water bottles last longest and make no meltwater mess. A few cups of rock salt on the cubes lowers the temperature of the melt and chills the fog further.
6. Aim the fogger. Set the fogger outside the cooler with its nozzle an inch or two from the inlet, not jammed inside it. The fogger needs air around it to cool its own housing, and the nozzle gets hot enough to soften plastic.
7. Close the lid, but do not latch it on dry ice. With plain ice the lid can close normally. If you ever add dry ice to a chiller, rest the lid loosely so gas can escape.

Running it

Foggers heat up for several minutes, fog for a short burst, then reheat. Short bursts work better than a constant stream anyway. A long continuous run warms the ice box quickly, the fog comes out lukewarm, and it rises again. A timer or remote set for a burst of 10 to 20 seconds every minute or two keeps the fog cold and low and makes the ice last.

Check the ice every hour or so and drain meltwater when it reaches the shelf. Never let meltwater run back toward the fogger.

A bigger trash can chiller for long nights

For a large yard or a long evening, a lidded plastic trash can holds far more ice than a cooler.

1. Cut an inlet hole near the top of the can and an outlet hole near the bottom on the opposite side.
2. Run 10 to 15 feet of flexible dryer vent duct in a loose coil inside the can, connecting the inlet to the outlet.
3. Pack ice around the coil all the way up.
4. Drill a few small drain holes in the base, or set the can on a couple of bricks over a gravel bed, so meltwater escapes.

The coil gives the fog a very long cold path, and the fog never touches the ice directly, so the duct stays cleaner. The tradeoff is weight. A trash can full of ice is heavy, so build it where it will sit.

The dry ice and hot water method

Dry ice fog is the thickest fog you can make at home. It is also the most hands-on. Reread the safety table at the top of this page before you start.

What you need

Making the fog

1. Set up outdoors on stable, level ground, away from the path where trick-or-treaters walk and away from steps.
2. Fill the pot about halfway with hot water. A little space at the top keeps bubbling water from spilling.
3. Add dry ice with tongs, a piece or two at a time. A pound or so in a couple of gallons of hot water gives a strong billow for several minutes.
4. Keep the water hot. As the dry ice chills the water, the fog weakens. Swap in fresh hot water every batch or two, or keep a second pot ready. For a continuous effect from one container over an hour, plan on several pounds of dry ice and a steady supply of hot water.
5. Hide the container, inside a cauldron prop, behind a tombstone, or under a stack of hay with gaps for the fog to spill out. Leave the top open so gas can escape.

Do not use dry ice fog indoors for a party, in a basement haunt, or anywhere guests sit, crouch, or lie on the floor. If you want fog inside a garage walkthrough, the fogger and chiller route is the safer choice, with the big door open for air. Our garage haunted house guide covers ventilation and exits for that setup.

Disposal. Leftover dry ice can sit in its loosely covered cooler outdoors, in a spot children and pets cannot reach, until it is gone. It leaves nothing behind.

Fog fluid choices

Use only fluid made for foggers, and match it to your machine.

Rules for fluid.

• Most fog fluids are a water-based glycol or glycerin mix. Use the type the machine's manual names. Glycerin-heavy fluid in a glycol machine can gum up the heater.
• Never put oil, alcohol, scented additives, or anything flammable in a fogger.
• Skip homemade fluid recipes. An overheated or wrong mix can clog the heater and produce irritating fumes.
• Do not mix fluid types in the tank. If you switch, run the machine until the old fluid is gone.
• Never let the tank run dry while the heater is on. Running dry damages the heat exchanger.
• Store fluid in the house, not a cold garage, if your manual warns about freezing.

Glycol fog can bother people with asthma. If a guest or family member is sensitive, keep the fog away from the door and the candy handoff.

Placing fog so the wind works for you

Fog is air you can see, so it goes exactly where the air goes. Placement matters as much as the machine.

Put the outlet upwind of the scene. Wet a finger or watch a strip of ribbon on a stake at dusk. Set the fog outlet on the side the breeze comes from, so the fog drifts across the display instead of away from it.

Know when wind wins. In still air or a light breeze, chilled fog can creep a surprising distance. Once the wind picks up to a steady breeze, fog shreds within a few feet no matter how cold it is. On a windy night, run fog in short bursts right at the base of the props people look at, rather than trying to fill the yard.

Build a windbreak. A row of props, a fence panel, a hedge, or the house wall on the windward side makes a calm pocket where fog pools. Fog also collects in low spots, so a slight dip in the lawn or the bed along the foundation holds fog far better than a raised bed.

Water the lawn in the afternoon. Damp, cool grass keeps the air right above it cooler and more humid, and fog lingers longer over it. Dry ice fog in particular looks thicker on humid evenings.

Hide the outlet. Run the outlet duct under a tombstone, into the base of a bush, or through a hole in a hay bale so fog appears to come from nowhere. For the graveyard itself, the props and their layout are in DIY outdoor Halloween decorations. A fog outlet under the porch rail makes a giant rope spider web look like it is floating over mist.

Use lights for the fog, not the fogger. Fog is invisible in the dark. A low colored flood aimed across the fog, not straight at the viewer, lights it up. A backlit flat figure is the best partner fog has, because the fog rolls across the glowing wall behind it and hides the stakes at its feet, and DIY Halloween yard silhouettes covers how to build and light one. A row of jack o lanterns along the fog path glows beautifully through it, and how to preserve a carved pumpkin keeps them standing until the big night. Use LED lights inside pumpkins that sit near a fogger or its cords.

Worked example: fogging a front yard graveyard

A graveyard bed along the front walk measures 20 feet long and 16 feet deep. The square footage calculator gives 320 square feet. Low fog looks best at a depth of about 6 to 12 inches.

Volume. At an 8 inch fog depth, that is 320 square feet times about 0.67 feet, or roughly 213 cubic feet of fog sitting over the bed at any moment. Chilled fog keeps warming and lifting away, so the machine has to keep replacing it in bursts.

Outlets. On a calm night, one chiller outlet spreads into a fan roughly 10 to 15 feet wide. A 20 foot bed needs two outlets. The simplest approach is one fogger feeding a cooler chiller with a Y fitting on the outlet duct, sending two runs to opposite ends of the bed. A larger yard with a stiffer breeze would use two foggers.

Placement. The breeze usually comes from the west in this yard, so the chiller sits at the west end, behind the tallest tombstone, with the two outlet ducts buried under mulch to their exit points. A fence panel on the west side acts as the windbreak.

Timing. The fogger runs a 15 second burst every 90 seconds from dusk to 9 p.m. The cooler starts with 20 pounds of ice and gets topped up once, around 7:30.

Safety layout. The chiller and fogger are at least 5 feet from the front walk, cords run along the back edge of the bed, and no fog outlet points toward the porch steps. The dry ice cauldron by the door is skipped this year because two toddlers and a dog live in the house.

The other safety rules: residue, heat, power, alarms

Fog residue makes surfaces slick. Glycol fog condenses as a thin film on smooth, hard surfaces. Porch steps, painted wood, tile, sealed concrete, and the walkway can all turn slippery after an hour of fog. Aim outlets away from steps and the main walk, check the steps with your shoe during the evening, and wipe them down with warm soapy water if they feel slick. Wipe the steps again the next morning.

The nozzle is hot. The front of a fogger gets hot enough to burn skin and scorch fabric. Keep it out of reach of children, away from dry leaves, straw, cheesecloth, and costume fabric, and let it cool fully before moving it.

Keep the fogger dry and the cords safe. Foggers are not waterproof. Set the machine on a block under a small roof or overturned tote with open sides, off wet ground, and plug it into a GFCI outlet with an outdoor-rated cord. A fogger's heater draws a lot of power, so avoid sharing its circuit with a big lighting display. Electrical safety basics shows how to add up the load on a circuit.

Smoke detectors indoors. Fog from any source can set off smoke alarms, and in some homes and apartment buildings the alarm is monitored and calls the fire department. Keep fog outdoors. Never cover, unplug, or remove the battery from a smoke detector to run fog inside. If fog does trigger an alarm, shut off the fogger and ventilate.

Visibility on paths. Fog over a lawn is spooky. Fog over a walkway hides a step, a hose, or a curb. Keep the path to your door clear enough that visitors can see their feet.

Cleaning and storing for next year

1. Run a cleaning cycle if your fogger's manual recommends one, using the cleaning fluid it names, so residue does not harden in the heater.
2. Empty the fluid tank or leave it as the manual directs. Some machines want the tank emptied, others want fluid left in the pump.
3. Rinse the chiller and ducts with warm soapy water, since fog residue collects inside. Let everything dry fully with the lid open before storing it, or it grows mildew.
4. Store the fogger indoors in its box, with the fluid, the remote, and the timer in the same bin.

Frequently asked questions

How do you make fog stay low to the ground?

Chill it. Run fogger fog through a cooler or trash can full of ice so it leaves colder than the outdoor air, which makes it heavier so it sinks. Use short bursts rather than a continuous stream, place the outlet low and upwind, and fog a sheltered, slightly low area. Low-lying fog fluid helps, but chilling makes the biggest difference.

Is dry ice fog safe for a Halloween party?

Outdoors, with sensible handling, yes. Indoors, it is a poor choice. The carbon dioxide sinks and collects at floor level, where children and pets breathe, and it stays there after the fog clears. Never handle dry ice bare handed, never seal it in a container, never put it in drinks, and keep it out of rooms where people sit or lie down.

How long does dry ice fog last?

A pound or so of dry ice in a couple of gallons of hot water fogs strongly for several minutes. As the water cools, the fog weakens, so fresh hot water keeps the effect going. For a steady effect over an hour from one container, plan on several pounds of dry ice and a supply of hot water.

Can I put dry ice in a fog chiller?

You can, but plain ice works well and is safer. If you add dry ice, never latch or seal the lid, keep the chiller outdoors, and handle the dry ice with gloves or tongs. A closed cooler with dry ice inside can build pressure.

Why is my fog machine fog rising instead of rolling?

The fog is leaving warm. Fogger fog is hot at the nozzle, and without a chiller it rises. Also check that the ice is not melted down, that the fogger is not running continuously, and that the fog is not being blown upward by wind hitting a wall or a slope.

Will a fog machine set off smoke detectors?

It can. Fog particles trigger many smoke alarms, and some are monitored and call the fire department. Keep fog outdoors, never disable a detector to use fog inside, and shut off the fogger and ventilate if an alarm sounds.

Does fog fluid make steps slippery?

Yes, over time. Glycol fog condenses into a thin slick film on smooth surfaces like steps, painted decks, tile, and sealed concrete. Aim fog away from steps and walkways, check the surface during the evening, and wash it with warm soapy water afterward.

Can I make my own fog fluid?

It is better not to. Homemade mixes can clog the heater, void the warranty, and produce irritating fumes if the ratio or temperature is wrong. Use the fluid type your fogger's manual names, and never add oil, alcohol, or fragrance.

Related: Build the graveyard your fog rolls through with DIY outdoor Halloween decorations, hang a giant rope spider web over the porch, and keep the jack o lanterns along the fog path fresh with how to preserve a carved pumpkin. Measure your fog zone with the square footage calculator.