Pad maintenance and mineral buildup
Every litre that evaporates leaves its dissolved minerals behind. Managing that concentration, plus algae and stagnant water, is most of evaporative cooler maintenance.
Why scale forms
Evaporation removes pure water vapour, so salts and minerals concentrate in the recirculating water and deposit on pads. In bad cases the deposits reduce evaporation efficiency, so the cooler gets warmer and airflow drops.[3] Harder supply water means faster buildup.
Controlling minerals: bleed-off vs dump pump
- Bleed-off: continuously drains a small stream to dilute minerals. DOE notes it can increase water use by 10–50%.[1]
- Dump pump / auto-flush: empties the pan and refills with fresh water at intervals, e.g. every 8–12 hours of operation. DOE calls this the more efficient alternative.[1]
- More is not always better: UC Davis WCEC testing on evaporative condensing units found that raising bleed beyond roughly 15% did not further reduce mineral deposits with high-mineral water. That study was on a related evaporative technology, not residential pad coolers, so treat it as indicative.[4]
- Start point and adjustment: the Illinois Extension (for agricultural pad systems) advises following the pad maker's recommendation, increasing bleed if scale appears, reducing it for softer water, and keeping pH roughly 6–8.[3]
The water use calculator shows how bleed-off and flushes add to consumption.
Algae and hygiene
- Let the pads dry fully once a day (e.g. run the fan only for a while after the pump stops) and keep sun off pads and the sump where possible.[3]
- Do not add bleach (chlorine) or bromine. They shorten pad life. Use cleaners approved by the pad manufacturer.[3]
- Drain the pan whenever the cooler will sit idle for more than a few days. Standing water can breed mosquitoes and bacteria including Legionella.[1]
Seasonal checklist (typical guidance)
These intervals are general guidance from the cited sources, not fixed rules. Your cooler's manual, your water hardness and how many hours you run the cooler should set the actual schedule.
| When | Tasks |
|---|---|
| Start of season | Replace or clean media; check belt tension and lubricate bearings; clean the cabinet and inspect for rust or damage; check that the pan holds water and the float works; aim water nozzles to saturate the pads.[1] |
| During season | In hot climates with heavy use, look at pads, filters, reservoir and pump at least monthly. A 2001 DOE fact sheet suggests replacing pads at least twice per season, or as often as monthly with continuous operation. Pad life varies with media type, water quality and maintenance.[2] |
| End of season | Shut off and drain the water line; drain, dry and clean the pan; remove mineral deposits; fit a cover; close dampers on ducted systems; remove window units.[1] |
Always disconnect power before servicing. Follow your cooler's manual where it differs from this general guidance.
Sources
- U.S. DOE Building America Solution Center (PNNL), "Evaporative Cooling Systems"
- U.S. DOE / NREL, "Cooling Your Home with Fans and Ventilation", DOE/GO-102001-1278 (2001)
- R. S. Gates, University of Illinois Extension, "Evaporative Cooling Pads"
- Western Cooling Efficiency Center, UC Davis, "Water Management for Evaporative Condensing Units"