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Sun, Jan. 19

Everything you ever wanted to know about evaporative coolers

An evaporative cooler.

An evaporative cooler.

Q: We moved to Prescott a few months ago. We rented a home with air conditioning until last week, when we moved into the home we bought. Our home is 10 years old and has an evaporative cooler with a large vent in the hall ceiling. We have not been happy with the evaporative cooler. The air does not seem to be very cool, and the paper coming out of my printer curls up like old-fashioned fax paper. We also get an occasional toilet odor that seems to be coming from the evaporative cooler. We have never heard of an evaporative cooler before moving here. Is this normal? What kind of maintenance is required? How hard is it to replace the evaporative cooler with central air conditioning?

A: To answer some of your questions, I'm copying the maintenance section from the evaporative cooler page in my inspection reports. (I figured I better admit this since anyone with one of my reports will recognize this.)

EVAPORATIVE COOLERS: Evaporative coolers are common in our area, and I know that some of you are not familiar with them. Coolers are relatively simple devices, are inexpensive to operate, and work very well in low humidity like we have here most of the time. Coolers have a water line that usually connects at a hose faucet, by the water heater, or sometimes under a sink. A cooler consists of a float valve, similar to the one in a toilet, that keeps the proper water level in the cooler. A small pump will circulate the water through small water lines, which will drop the water on the pads. A blower will pull air through the wet pads and deliver it into the home. The water evaporating off the pads is what cools the air. (If you get out of a swimming pool on a hot day, you are cool until you dry off. The water evaporating off your body cools you. This is the same principle.) Pads, pumps and float valves are maintenance items that occasionally need replacing. They are usually readily available and not major expenses. Not much maintenance is required other than draining the cooler and water line before winter and giving it a thorough check and cleaning before summer. To drain the cooler you remove the plug in the bottom of the cooler. You should also drain the water line by removing the line from the cooler, and then removing the line at the valve (use a bowl if needed to catch the water). Most people cover rooftop units during the winter months. If your evaporative cooler has one or two supply vents in the home, slightly opening a window in a room will help circulate cool air to that room. If your cooler is connected to a central furnace, there should be dampers. This damper is often a piece of metal ("cookie sheet") that slides into the duct or cooler. Sometimes the damper in the furnace is a board or piece of metal placed over the filter. A damper is installed in or near the cooler when the furnace is in operation to keep warm air from escaping out the cooler. When the cooler is in use, the damper in or near the furnace will keep humid air from being blown through the furnace heat exchanger. I often find the damper near the furnace missing, and it is important. Sometimes the ducts have automatic dampers in the cooler or attic, and sometimes these dampers are hard to locate. In these instances, the report will state to verify the existence and location of the dampers with the Seller. To check for a damper, or if an automatic damper is operating correctly, open the furnace blower compartment (often where the filter is) when the cooler is operating. If you feel cold air blowing out of the furnace, the damper is missing or defective (unless of course the damper is in this compartment). NOTE: Never operate a furnace without removing the damper in or near the furnace!

That answered some of your questions, and made it easier to understand the rest of my answers. Since water evaporating off the cooler pads is what cools the air, the higher the humidity the less effective a cooler. This is why many areas of the country do not have evaporative coolers at all - they are not efficient in humid climates. You moved into your new home during monsoon season, when our humidity is at its highest and your cooler is least efficient. This would also explain your curling printer paper - right now, your cooler is increasing the humidity levels in your home much more than it will when it's dry outside. The monsoons will be over in a couple weeks, and your cooler will work better and my motorcycle will come out of my garage.

You cannot "replace" your cooler with a central air conditioner. If you have a central furnace, you can add central air conditioning to the furnace and remove the cooler. Or you can keep the cooler and have the best of both worlds. You can use the cooler when it's dry or only moderately hot, and the air conditioner when it's humid outside or really hot.

You mentioned an occasional "toilet" odor. I assume you mean sewer odor, since toilets don't really have an odor until someone uses them after eating the wrong food the night before. I'm assuming your cooler is on your roof. Your plumbing vents are also on your roof. The plumbing vents are black plastic pipes (they could be metal or white plastic, but you stated your home was 10 years old so they are likely black plastic). These vents allow plumbing fixtures to drain properly, and they do emit sewer gas/odors occasionally. The first thing I would check is if you have a plumbing vent pipe near the cooler on the roof. An evaporative cooler pulls a lot of outside air through the pads and into the home, so if there is a plumbing vent nearby it could be pulling some of the sewer gas/odor into the home. It is a very minor task for a plumber to alter or relocate the plumbing vent to eliminate this problem.

Randy West owns Professional Building Consultants in Prescott.

He is a state-certified home inspector, and has performed more than 4,000 home inspections in the Prescott area. West is president of the Arizona Chapter of the American Society of Home Inspectors (ASHI), and currently serves on the Enforcement Advisory Committee for the Arizona Board of Technical Registration. Contact him at

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