#099 — Swamp Cooler
Evaporative AC from a bucket, a fan, and a pump. Drops room temperature 15-20°F using only water.
Ratings
🧪 What Is It?
Evaporative cooling is the oldest AC on earth — it's why sweating works. Water evaporating absorbs heat from the air, dropping the temperature. A swamp cooler pulls air through a wet medium (pads, towels, or excelsior), evaporating water and blowing cold, humid air out the other side. In dry climates, these are devastatingly effective — 15-20°F temperature drops for the cost of running a fan and a small pump. Build one from a 5-gallon bucket, a fan salvaged from any dead appliance, and a small aquarium pump.
🧰 Ingredients
- 5-gallon bucket with lid (hardware store, ~$3)
- Fan — 120mm PC fans, bathroom exhaust fan, or any small salvaged fan (salvage from dead PC, appliance)
- Small water pump — aquarium pump or dishwasher drain pump (salvage or pet store, ~$5)
- Cooling pads — excelsior, burlap, or thick sponge material (hardware store, craft store)
- PVC pipe or tubing — for water distribution (hardware store)
- Drill and hole saw (for cutting ventilation holes)
- Water (tap)
🔨 Build Steps
- Cut intake holes. Drill or cut large rectangular holes in the sides of the bucket. These are where warm air enters. Cover them with the cooling pad material — the air must pass through the wet pads.
- Cut exhaust hole. Cut a circular hole in the lid sized to fit your fan. This is where cold air blows out.
- Mount the fan. Attach the fan to the lid, blowing outward (pulling air through the wet pads and pushing cool air into the room).
- Install the pump and distribution. Place the pump in the bottom of the bucket in a few inches of water. Run tubing from the pump up to the top of the cooling pads. Poke small holes in the tubing so water drips evenly across the pads, keeping them wet. The water drains back to the bottom and recirculates.
- Fill with water. Add water to the bucket — enough to submerge the pump and keep the reservoir fed. Top off as it evaporates (a few gallons per day in hot weather).
- Power up. Plug in the fan and pump. Within minutes, the output air should be noticeably cooler than ambient. Measure with a thermometer — in dry climates (below 40% humidity), expect 15-20°F drops.
- Optimize placement. Works best with a window open on the opposite side of the room to create cross-ventilation. The swamp cooler adds humidity, so it needs somewhere for the moist air to exit.
⚠️ Safety Notes
- Change the water daily in humid climates to prevent mold and bacterial growth. Add a capful of bleach to the reservoir to inhibit growth.
- Swamp coolers only work well in dry climates (below 50% relative humidity). In humid climates, they just make the room muggy without meaningful cooling.