DIY Swamp Cooler: How to Build One and How Much Cooling to Expect

You can build a working swamp cooler from a 5-gallon bucket, a small fan, a fountain pump and some cooler pad, and in dry heat it will blow air 10 to 20 F cooler than the room. What it will not do is cool a room. A typical bucket build moves 50 to 150 cubic feet of air per minute through its pad, which works out to roughly 1,000 to 2,000 BTU per hour of cooling: enough to make one person at a desk, in a tent or in a workshop corner much more comfortable. The popular ice-chest "air conditioner" is a different device altogether. It is not evaporative, and it runs out of cooling within a few hours.

This page gives you the math to set honest expectations, then the build steps for the designs that work best.

Three DIY designs, and which ones are evaporative

A true evaporative cooler works by turning liquid water into vapor. Each pound of water evaporated absorbs about 1,060 BTU from the air. That is a huge amount of cooling per pound, and the supply of it is essentially unlimited as long as you add water. The catch is that the air can only be cooled toward its wet bulb temperature, so this works well in dry climates and poorly in humid ones. If you want the full mechanism, see how evaporative coolers work.

An ice chest cooler works by melting ice. It cools air regardless of humidity, but each pound of ice absorbs only about 144 BTU while melting, and once it is gone, the cooling stops.

Worked example: what a bucket cooler really delivers

The key numbers are airflow through the pad, the pad's saturation efficiency, and the gap between dry bulb and wet bulb.

Now the same cooler in a sealed bedroom. The cooler adds moisture to the room air, so the room's wet bulb climbs. After an hour or two of recirculating, the supply might only be 3 to 6 F below room temperature and the room feels clammy. Ventilation is not optional, even at this scale. Our cooling temperature calculator shows how much your conditions allow.

The ice chest cooler: honest math

The viral ice-chest design is a picnic cooler with a fan in the lid blowing over ice, and PVC elbows as outlets. It does blow cold air, often in the 40s and 50s at first. It is not a swamp cooler, though, and the numbers explain why it disappoints.

There is a hidden cost too. If you make the ice in a home freezer, the freezer rejects the ice's cooling plus its own compressor energy as heat into your kitchen. Inside a house, the net effect on whole-house heat is roughly zero or slightly negative; you are moving coolness from the kitchen to your chair. Ice from a store, a large chest freezer in the garage, or frozen water bottles from a camp cooler changes that equation.

Where the ice chest wins: it works in humid climates, where an evaporative cooler barely helps, and it adds no moisture to the room. Frozen gallon jugs instead of loose ice avoid the meltwater mess and can be refrozen.

How to build a bucket swamp cooler

Bucket

5 gallon food-grade bucket with lid (typically $5 to $10)

Fan

12 V DC fan (computer or RV type, 120 mm or larger) or a small 120 V desk fan that fits the lid

Pump

Small submersible fountain pump, about 50 to 150 gallons per hour, 12 V or 120 V (typically $10 to $25)

Tubing

1/4 in or 3/8 in vinyl tubing to match the pump outlet, with a few small holes or a drip ring

Media

Aspen cooler pad cut to size, or scrap rigid media; see types of pads

Tools

Drill, 2 to 3 in hole saw, utility knife, zip ties; optional 1-1/2 in PVC elbow for an outlet

Time

About 1 to 2 hours

1. Cut intake holes. Drill four to six 2 to 3 in holes around the bucket, starting 4 to 5 in above the bottom so the water reservoir sits below them. More open area means more airflow.
2. Line with media. Wrap a strip of aspen pad or rigid media around the inside wall, covering every hole. Hold it in place with zip ties through small holes or a ring of hardware cloth.
3. Install the pump. Set it on the bottom. Route tubing up to a ring just above the top edge of the media, poke small holes in the ring (about 1/16 in), and close the end. Water should trickle evenly down the full pad.
4. Mount the fan. Cut a hole in the lid to match the fan and mount it blowing out, so it pulls air in through the wet pad and up. Add a PVC elbow if you want to aim the outlet.
5. Wire safely. With 12 V parts, wire to a battery or adapter with an inline fuse. With 120 V parts, plug into a GFCI-protected outlet and keep cords and connections above the waterline and out of the airflow drip path.
6. Fill and test. Add 2 to 3 gallons of water below the holes. Run the pump for a few minutes to soak the pad, then start the fan. Check for dry spots and splashing.

The bigger build: box fan and window pad

If you want to cool a small room or a garage bay, the most effective DIY setup is a 20 in box fan blowing through a wet pad mounted in an open window, with water dripped onto the top of the pad from a small pump in a tray below.

• Airflow. Box fans move roughly 1,500 to 2,500 CFM in free air on high, but a wet pad adds resistance. Assume roughly half.
• Estimate. At 1,000 CFM through the pad and a 15 F drop: 1.08 x 1,000 x 15 = 16,200 BTU/h. Even at 500 CFM and a 12 F drop, about 6,500 BTU/h. That is real room cooling in dry heat.
• Water. 16,200 / 1,060 = about 15 lb, or roughly 1.8 gallons per hour. Use a float-fed tray or a large reservoir.
• Relief. Open a window on the far side of the room or house, just as you would with a full-size cooler.

At this point, compare honestly with buying. A small commercial portable or window evaporative cooler often costs $100 to $400 in 2026, with a properly designed pad, float, louvers and a pump sized to the media. See our portable cooler buying guide and window cooler guide.

Getting the most from a DIY cooler

• Use real cooler media. Towels and sponges choke airflow and mildew quickly.
• Keep the media fully wet. Dry patches pass warm air straight through.
• Start with cool water but do not depend on it. Cold water helps for the first few minutes only; evaporation sets the steady-state temperature.
• Place it close. Within 3 to 6 ft of you. The airstream warms quickly as it mixes with room air.
• Vent the space. Fresh air in, humid air out.
• Check the weather. If the outdoor wet bulb is above about 72 F, a plain fan or an ice-based design will do about as well. Look up your city in the climate index.

Safety and hygiene

• Empty and dry daily. Stagnant warm water in a bucket grows algae, bacteria and mold within days. Pour it out, let the media dry, and refill fresh.
• Clean weekly. Scrub the bucket and rinse the pump intake screen.
• Replace media when it smells musty or shows growth. Aspen is cheap.
• Do not rely on a DIY cooler in dangerous heat. In extreme heat, especially for older adults, infants or people with health conditions, follow National Weather Service heat guidance and seek reliable cooling such as a cooling center.

Built and used with realistic expectations, a DIY swamp cooler is a cheap, effective personal cooler for dry climates. For anything bigger than one person or one small room, a purpose-built unit sized with our cooler size calculator will do far more for similar effort.