How to Replace Swamp Cooler Pads, Step by Step

Replacing swamp cooler pads is the most common cooler maintenance job, and one of the most rewarding: fresh pads can lower supply air temperature by several degrees compared with tired, scaled ones. The job is simple: power off, panels off, old pads out, clean, new pads in with no gaps, panels on, pre-wet. The details that separate a good pad change from a mediocre one are measuring the frame correctly, seating pads tightly, and cleaning the water distribution while you are in there.

Tools, materials and time

Tools

1/4 in and 5/16 in nut drivers (common for cabinet screws), flat screwdriver, heavy scissors or utility knife, tape measure, stiff brush, shop vacuum, small drill bit or paper clip for trough holes, work gloves, safety glasses.

Materials

Replacement pads for your cooler size, pad retainer clips or wires if old ones are damaged, a few spare cabinet screws, white vinegar for scale.

Time

About 45 to 90 minutes for a whole-house aspen cooler, 20 to 40 minutes for a window or portable unit, and 1 to 2 hours for rigid media including header cleaning.

Best timing

At spring startup, plus midseason when aspen shows thinning or scale. See how often to replace cooler pads.

Buying the right pads

Measure the inside of a pad frame (the louvered panel), not the old pad, which has shrunk. Aspen pads come in pre-cut sizes for common coolers and in bulk rolls you trim. Synthetic pads come in pre-cut sizes. Rigid media must match the cooler's specified height, width and thickness exactly, usually from the cooler manufacturer or a parts supplier.

Pre-cut aspen pad sets for whole-house coolers are typically about $20 to $80 in 2026, varying by size and region. For a comparison of materials, see types of evaporative cooler pads.

Replacing aspen or synthetic pads, step by step

1. Shut down power and water. Turn off the wall control, then the disconnect or breaker. Close the supply valve to the cooler.
2. Drain the pan. Pull the overflow standpipe or open the drain. Aspen debris and sludge come out more easily with the water gone.
3. Remove the side panels. Remove the screws (or lift the panels off their hooks on some models) and set the panels flat, louvers down, on a clean surface. Keep screws in a container; dropped screws roll into gutters and down roofs.
4. Remove old pads and retainers. Bend back or unclip the retainer wires, pull the old pads out, and bag them immediately so fibers do not blow into the cabinet. Note how the pads and retainers were arranged.
5. Clean the louver panels. Brush out the scale and debris. Clear the water trough at the top of each panel and every hole in it with a small bit or paper clip. Soak heavily scaled troughs with white vinegar. Check panels for rust-through and coat any rust spots.
6. Clean the cabinet while it is open. Vacuum debris from the pan, scrub any sludge, clean the pump intake screen and flush the spider and tubes. This is also a good time to check belt tension and the float level. The cleaning guide covers this in detail.
7. Fit the new pads. Lay each pad in its panel, denser or marked side toward the louvers. Push it into the corners so it fills the frame edge to edge with no gaps along the top. A pad that is too large should be trimmed, not folded; folds create thick spots that do not wet.
8. Secure with retainers. Reinstall retainer wires or clips so the pad stays pressed against the louvers and cannot sag. Replace any bent or rusted retainers.
9. Reinstall panels and check alignment. Seat each panel so its trough sits directly under its distributor tube. Tighten screws snugly; do not strip the cabinet holes.
10. Restore water, then power. Open the supply valve and let the pan fill to the correct level (about 1/2 to 1 in below the overflow top). Restore power.
11. Pre-wet and inspect. Run the pump alone for 5 to 10 minutes. Check from outside that every pad is evenly dark and wet, with no water spraying out of the louvers. Then start the fan.

Replacing rigid media, step by step

Rigid media coolers vary more by model, so follow the manual, but the core procedure is consistent:

1. Power and water off, drain. As above.
2. Remove the media access panels or retainers. On many rigid coolers the media slides out of channels after a top cap or retaining bar is removed.
3. Lift the media out carefully. Wet rigid media is heavy and its edges are fragile. Lift from the bottom and support the block; do not pull by the top edge.
4. Clean the distribution header. Flush the header pipe or pad, clear every outlet hole, and check that the spreader on top of the media is intact. Even top-edge wetting is critical with rigid media.
5. Note the orientation of the new media. Rigid media has cross flutes at two different angles. Install it per the label, usually with the steeper flute angle sloping down toward the air-entry side so water drains toward the outside face and is not driven toward the blower. Installed backward, it can shed water into the airstream.
6. Seat and seal. Slide the media into its channels so it sits fully down and fits tightly side to side. Fill any gap with the manufacturer's seal strip; even a 1/4 in gap lets a meaningful share of air bypass the media.
7. Reassemble, refill and pre-wet. Run the pump for 10 minutes and watch the full face darken evenly before starting the fan.

Replacing pads in portable and window coolers

Smaller coolers follow the same principles with simpler hardware:

1. Unplug and empty the tank. Portables should be unplugged, not just switched off. Pour out or drain the tank.
2. Remove the rear grille or pad frame. Usually a few screws or clips. Note how the pad sits relative to the water distribution tube at the top.
3. Install the model-specific pad. Portable media is often thin honeycomb with a marked top or air direction; follow the arrow. Make sure the top edge sits directly under the distribution tube.
4. Clean the tank and pump inlet. Scrub the tank, rinse the pump screen, and flush the distribution tube.
5. Refill and pre-wet. Fill to the marked level and run the pump or cool mode with the fan on low for a few minutes, watching that the whole pad darkens.

Window coolers with aspen pads work like smaller versions of side-draft units: remove the louvered panels, swap and trim the pads, clear troughs, and reinstall. Check that the cooler still tilts slightly outward so excess water drains outside; see window cooler installation.

Common mistakes to avoid

• Gaps along the top of aspen pads. Hot air takes the easy path. A 1 in strip of bare louver across a 28 in panel is about 28 sq in of unfiltered, uncooled air.
• Misaligned troughs and tubes. Water hits the side of a trough and runs down the louver instead of into the pad.
• Skipping the pump screen. Old aspen fibers left in the pan clog the pump within days.
• Installing rigid media upside down or backward. Cooling drops and water can blow into the duct.
• Running the fan on dry pads. New aspen gives off dust and a woody smell until wet.

After the change: confirm the result

Measure supply air temperature at a nearby register and compare it to the expected value from the cooling temperature calculator. Fresh, fully wet aspen should come within about 20 to 35% of the dry bulb to wet bulb gap above the wet bulb; 8 in rigid media should come within about 10 to 15%. If it falls short, look for dry streaks and gaps, then work through swamp cooler not cooling. Pair this job with the rest of your spring startup checklist, and if you are deciding whether to upgrade materials, read aspen vs rigid media.