Air Cooler Cooling Pads: Honeycomb, Aspen and Wood Wool Compared

The pad is the evaporation surface. Water trickles down it from the pump, air is pulled through it by the blower, and water evaporates off that wetted surface into the airstream. Everything about the cooler's performance depends on how much wetted surface the air meets and how evenly the water is distributed across it.

That is why pad type matters more than most of the features listings advertise. A cooler with a strong blower and poor pads moves a lot of barely-cooled air.

On total cost of ownership honeycomb usually wins even though it costs the most to replace, because it lasts two to three times as long and can be cleaned rather than swapped.

• Rinse the pads with plain water every three to four weeks through the season. Do not scrub honeycomb hard — the cellulose structure is what does the work.
• Drain the tank whenever the cooler will be idle for more than a couple of days. Standing warm water is where both the smell and the microbial risk come from.
• At the end of the season, run the blower without the pump for half an hour to dry the pads, then store the unit dry and covered.
• If the pads have hardened, gone white with mineral scale, or smell after rinsing, replace them. On a honeycomb set that is typically every second or third season.
• In hard-water areas, descale the tank and distributor holes — blocked holes leave dry patches on the pad, and a dry patch is airflow that is not being cooled at all.