Through my years of working on evaporative coolers I have found that poor maintenance of cooler pad material probably contributes the most to premature deterioration of the entire cooler. Most owners feel they are saving money by leaving the old pads in the unit for as long as possible but, ultimately they are costing themselves much more money in the long run by having to change out the entire cooler years before they should have to change it. I will explain why this is usually the case. But first let’s look at the different types of evaporative cooler media.
The most common pad material for evaporative coolers is aspen pad. These pads get their name because they are made of wood shavings from small cooler aspen trees. The aspen wood is then enclosed in plastic cheesecloth mesh sized for each evaporative cooler louver. Aspen pads are very commonly used because the aspen shavings absorb and release moisture very efficiently. By releasing more water into the passing air, the temperature drop using aspen pads is better than some other materials. Although these aspen pads are not as efficient as CELdek media, which is cellulose paper engineered into honeycomb shaped blocks. CELdek media generally comes in 8 in. and 12 in. thick blocks. Since the air passes through thicker material more water is absorbed which gives a greater temperature drop to the air. Since aspen pads are far less expensive to manufacture they are more commonly used in evaporative coolers.
So why should you change aspen pads every year even though they do not look that bad after one year? Your float valve lets many gallons of water into the cooler each day. As the water distributes over all the aspen pads it is constantly evaporating. This is good as it produces cool air. But on the other hand it is leaving all the original minerals from these gallons of water each day to keep building up in the cooler pan. As this heavily mineraled water pumps into the aspen pads, these pads hold much of the minerals. Remember in these types of coolers the aspen pad is in contact with the metal louvers. These minerals being held against the metal louvers can deteriorate the louvers years before they should.
From my experience, most evaporative cooler owners do very little maintenance and complain that the coolers do not last long enough. Others, who do end of the year maintenance, drain and clean the cooler pan and feel they are taking good care of their cooler. But they are leaving a large amount of minerals in the cooler pads through the winter, waiting to deteriorate the metal as soon as the next cooling season starts. Residential cooler pads about $7 each and depending on whether your cooler is a window mount, side draft or down draft roof top unit, you are only using 3 or 4 pads per cooler. Spending $20-$30 per year on aspen cooler pads can usually be far less expensive than buying and installing a new cooler years before you need to. I hope this help to think about changing your cooler pads each year.