How often to replace swamp cooler pads: 6 signs it's time

Short answer: University of Arizona Extension suggests new aspen pads each spring. MasterCool rates its rigid media at about 5 years, and less where water is very hard. PNNL says to replace any pad that is torn, worn, or mildewed. Here are six signs to check.

1 It's spring and you have aspen pads

University of Arizona Extension's spring checklist includes installing new pads: "Aspenwood fiber pads are a good choice, or follow manufacturer's recommendations." PNNL says spring start-up is the time to replace or clean the media.

Next step: Look up your pad size and count in the pad finder.

2 The pads are torn or worn thin

PNNL's maintenance list says plainly: "Replace torn, worn or mildewed cooler pads." Holes and thin spots let air bypass the wet media.

Next step: Measure the pad frame, then match it in the pad finder.

3 You see or smell mildew

Mildewed pads are on the same PNNL replace list. PNNL also warns that standing water left in the pan can breed mosquitoes and bacteria, including Legionella, and says to drain the pan if the cooler will sit idle for more than a few days.

Next step: Replace the pads, then follow the in-season tips in the Albuquerque guide.

4 The pads don't soak evenly

UA Extension says to run the pump and check that the pads saturate evenly. Dry streaks aren't always the pad's fault. PNNL says to check that water nozzles are aimed to saturate the pads and to clean them with vinegar to remove calcification. Clean the distribution system first, and replace pads that still won't wet through.

Next step: Work through the 8-step start-up checklist.

5 Hard mineral crust has built up

Albuquerque's water utility (ABCWUA) says its water ranges from "moderately hard to hard," and that dissolved minerals are "the residue that collects on evaporative coolers during the summer months." MasterCool says rigid media may need replacing sooner than 5 years in areas with very high mineral content. A bleed-off valve reduces buildup but increases water use by 10–50% (PNNL).

Next step: Read the hard-water section of the Albuquerque guide.

6 Your rigid media is about 5 years old

MasterCool: "The original media has a standard life of 5 years." Rigid media has to match your cooler's depth (8" or 12") and size, and MasterCool's universal media chart lists which models each set fits.

Next step: Find your media set in the pad finder, or compare options in the product links below.

Sources

1. University of Arizona Cooperative Extension, Cochise County Water Wise
2. PNNL / DOE Building America Solution Center, “Evaporative Cooling Systems”
3. MasterCool ADA51/71 owner's manual
4. MasterCool Universal Rigid Media chart
5. ABCWUA drinking water FAQs

Published October 30, 2026. These are general tips; follow your cooler's manual where it differs.

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