10 Disadvantages of Evaporative Cooling and How to Offset Them

The disadvantages of evaporative cooling are real, but nearly all of them are predictable and manageable once you understand what causes them. Evaporative coolers, often called swamp coolers, cool air by passing it through water-soaked pads, and that simple process comes with limits: humidity, water use, maintenance habits, and the heat load of the space you are cooling. Knowing those limits before you buy, or before you blame your current unit, saves money and frustration.

If you are weighing evaporative cooling systems for a home, shop, or warehouse, the ten drawbacks below explain what the data says about each one and how to offset it. The goal is not to talk you out of evaporative cooling. It is to help you decide whether it fits your climate and your building, and how to get the most from it if it does.

Why Evaporative Coolers Have Limits

Evaporative cooling is efficient because it uses a fan and a small pump instead of a compressor. The U.S. Department of Energy reports that evaporative coolers cost about half as much to install as central air conditioners and use about one-quarter as much energy. The same physics that makes them efficient also sets their limits. A direct evaporative cooler cannot cool air below the wet-bulb temperature, which is the lowest temperature air can reach by absorbing water vapor. In practice, the better the cooler, the closer it gets to that limit, but it never passes it.

The 10 Disadvantages of Evaporative Cooling and How to Offset Each One

1. It Loses Cooling Power in Humid Climates

This is the biggest drawback. Dry air can absorb a lot of water vapor, so evaporation removes a lot of heat. Humid air is already close to saturation, so very little cooling is available. The Department of Energy says evaporative coolers are only suitable for areas with low humidity and should not be used in humid climates. A federal technology review shows how steep the drop-off is: 95°F air at 70% relative humidity could be cooled only about 9°F, while the same air at 10% humidity could be cooled about 35°F.

Sources: NREL and U.S. Department of Energy, Coolerado Cooler Helps to Save Cooling Energy and Dollars and Stull, Journal of Applied Meteorology and Climatology (2011)

How to offset it: Check your local afternoon humidity, not the morning reading, because humidity drops as temperatures rise. On rainy or very humid days, run the fan without the pump, which the New Mexico Office of the State Engineer recommends when a cooler is significantly less efficient.

2. It Uses Water

Evaporative coolers consume water by design. A study of 46 Phoenix homes cited by NREL found direct coolers used about 4.4 gallons per hour without bleed-off and about 10.4 gallons per hour with bleed-off. The New Mexico Office of the State Engineer estimates that a 1,500 square foot home might use roughly 3,000 gallons per season in Santa Fe, over 7,000 in Albuquerque, and over 12,000 in Las Cruces, with bleed-off adding 50% or more.

Source: New Mexico Office of the State Engineer, Water Use and Conservation Bureau

How to offset it: Replace continuous bleed-off with a dump pump that empties the pan at intervals, wait until it is about 85°F instead of 79°F to start the cooler (the same agency says this can cut water use by half), and run only the fan in the evening. Check lines and connections monthly, because leaks waste more water than people realize. Replacement floats and water-line parts are inexpensive.

3. It Adds Humidity Indoors

A swamp cooler works by moving moisture into the air, so the house gets more humid as it runs. In a dry climate that can feel pleasant. When moisture cannot escape, the air turns clammy. The EPA suggests keeping indoor relative humidity below 60%, ideally between 30% and 50%, and notes that condensation on windows can be a sign of high humidity.

Source: U.S. Environmental Protection Agency, Mold Course Chapter 2

How to offset it: Open a window in each room you want cooled so humid air can leave, since direct coolers are open systems that need windows or exhaust vents to stay open. A two-stage cooler is another option. The Department of Energy says two-stage units do not add as much humidity as single-stage coolers.

4. Mold, Algae, and Odors Appear When Maintenance Slips

Constantly wet pads and a standing reservoir create the right conditions for biological growth if they are neglected. The EPA notes that eliminating all mold indoors is virtually impossible, but controlling moisture controls its growth. Illinois Extension adds that algae increases airflow resistance and breaks down cellulose pad material, and it recommends letting pads dry completely once every 24 hours. It also advises against chlorine bleach on cellulose systems because it shortens pad life.

How to offset it: Run the fan with the pump off before shutting the cooler down so the pads dry, scrub the reservoir regularly, and treat a musty smell as a signal to clean. When pads are thin, crusted, or discolored, fresh replacement evaporative cooler media resets the system.

5. It Cannot Cool as Low as Air Conditioning

The Department of Energy states plainly that evaporative coolers do not cool a house as low as an air conditioner would. The wet-bulb limit is the reason. The New Mexico Office of the State Engineer gives a typical example: at 30% relative humidity, an evaporative cooler can bring 90°F air down to a comfortable 74°F. That is a large drop, but it is not a set-point you can dial in, and on the hottest, stickiest days the result is smaller.

How to offset it: Set realistic expectations, aiming for a meaningful drop from outdoor temperatures instead of a specific number. Reduce heat gain with shade and closed blinds, and consider a two-stage design for hotter conditions.

6. It Needs More Frequent Maintenance

Evaporative coolers are mechanically simple, but they need regular attention. The Department of Energy recommends simple maintenance about once a month and a major cleaning every season. The New Mexico Office of the State Engineer outlines a spring start-up, monthly summer inspections, and a fall shutdown, and notes that some manufacturers recommend replacing pads at least once during the cooling season because old pads get coated with minerals and absorb less water.

How to offset it: Put the schedule on a calendar, keep spare pads and a belt on hand, and choose durable media. Rigid cellulose products such as long-lasting CELdek media hold their shape and are easier to keep clean than loose fiber pads.

7. Outdoor Air Quality Comes Indoors

Evaporative coolers bring in fresh outdoor air continuously, which is a benefit and a drawback. The New Mexico Office of the State Engineer notes that wet pads remove some dust and pollen. However, the Department of Energy points out that most evaporative coolers do not have air filters as original equipment. On smoky or high-pollen days, the air entering the home is only as clean as the air outside.

How to offset it: Add a filter, which the Department of Energy says can be fitted during or after installation, keep the pads clean, and run the cooler less on smoky days.

8. Temperature Control Is Less Precise

An air conditioner cycles a compressor to hold a set-point. An evaporative cooler delivers whatever the weather allows. Because the outdoor wet-bulb temperature changes through the day, indoor temperatures drift too. The cooler often performs best in the hottest part of the afternoon, since relative humidity falls as temperatures rise.

How to offset it: Use fan speeds to match the weather, adjust window openings room by room, and start the cooler before the house has built up heat instead of waiting until it is already hot. Many owners find the drift is a fair trade for lower operating costs.

9. It Needs Ventilation and the Right Installation

The Department of Energy notes that most residential coolers are installed in a down-flow arrangement on the roof, and that coolers with up-ducts need additional attic ventilation. Because direct coolers are open systems, windows or exhaust vents must stay open, so a tightly sealed building does not work well. Contrary to a common assumption, window and portable units do not need ductwork at all.

How to offset it: Plan the exhaust path before installation, and match the unit to the building. Rooftop and window systems from our line of evaporative coolers for homes are sized for different layouts, and a qualified installer can confirm that your windows and attic provide enough relief.

10. High Heat Loads Can Overwhelm It

Evaporative coolers are rated by the cubic feet per minute (CFM) of air they deliver, and sizing is based on the building’s square footage and the air changes it needs per hour. A building with large west-facing windows, poor insulation, or heat-producing equipment can outrun a unit that was sized for an average load. Undersizing is the most common reason an otherwise healthy cooler feels weak.

How to offset it: Cut heat gain first with shade, insulation, and efficient lighting, then confirm the cooler’s capacity. Compare the airflow ratings and dimensions to your space before you buy or upgrade, and move up a size if the load is high.

Quick Reference: Each Disadvantage and How to Offset It

Who Should Think Twice About Evaporative Cooling?

Are the Disadvantages of Evaporative Cooling Deal Breakers?

For most dry-climate buildings, no. They become deal breakers in a few situations:

• Humid summers: If your region stays muggy for weeks at a time, the cooling effect will be small.
• Tight water limits: If water is restricted or expensive, factor in several thousand gallons per season.
• A need for exact temperatures: Labs, server rooms, and some storage areas need set-point control.
• No time for upkeep: A neglected cooler loses performance and develops odors quickly.
• Sealed buildings: Without an exhaust path, direct coolers do not work as designed.

Options That Reduce the Drawbacks

You do not have to choose between a full system and nothing. Spot cooling can solve many problems, and portable swamp coolers let you cool a garage, workshop, or single room without ductwork or a rooftop installation. The Department of Energy notes that small portable units typically reduce room temperature by about 5°F to 15°F.

Large facilities have different needs. Plants, warehouses, and workshops often combine high heat loads with open floor plans, which is where industrial evaporative cooling systems are designed to perform, moving large volumes of air and exhausting it through the building envelope.

Get Expert Help Choosing the Right Cooler

Every drawback above comes down to matching the equipment to the climate, the building, and the way it will be used. A seasoned evaporative cooling manufacturer can size the airflow, specify the right media, and plan the exhaust path so the system performs the way you expect.

If you want a straight answer on whether evaporative cooling fits your space, you can talk with an evaporative cooling specialist about your climate, your square footage, and your heat load.

Frequently Asked Questions About the Disadvantages of Evaporative Cooling

Categorised in: Evaporative Cooling

This post was written by Premier Industries Team