Do Swamp Coolers need open windows?

Ever wondered if you need to leave your windows open for your swamp cooler to work effectively? The answer is no.

Quick answer: No, swamp coolers do not need open windows to operate effectively. For optimal performance and energy efficiency, it’s better to keep windows closed and control the indoor humidity through regular venting.

In fact, your cooler performs best with your windows closed and occasional venting. This contrasts with several misconceptions about swamp coolers: that the increased humidity must be constantly vented out, that longer running times lead to higher humidity, and that open windows help airflow. In this post, we’ll bust these myths and give you a clear guide to using your swamp cooler more efficiently.

Why do swamp coolers not need open windows?

We’ve tackled some common misunderstandings about swamp coolers in this post.

  • Myth #1: Swamp coolers create humidity and the humidity needs to leave the house as soon as possible
  • Myth #2: the longer a swamp cooler runs, the more humid the air (false!)
  • Myth #3: open windows help the swamp cooler’s airflow

By understanding these points, you’ll be able to make your swamp cooler work efficiently, keeping your home comfortably cool.

Mythbusting: Why swamp coolers don’t need open windows

Let’s check each myth in depth:

Myth #1: Swamp Coolers require constant venting

Swamp coolers work by evaporating water into the air, thereby increasing its humidity. It’s a common assumption that this increased humidity is harmful and must be constantly vented out. However, this belief doesn’t quite hit the mark.

The fear of humidity comes from the idea that it could potentially damage a house’s structure. Yet, if humidity alone were enough to degrade a house, dwellings in humid climates, such as those in Florida or Central Europe, would be short-lived.

Air humidity does not harm your house, but dew does

The actual threat to houses is not humidity per se, but dew formation. Dew forms when humid air cools quickly, like during the night, causing the water vapor in the air to condense.

The condensed water, or dew, can then interact with certain materials, like wood, leading to potential water damage over time.

When our dog spills water on the wooden floor, within a couple hours the floor soaks up the water and deforms and discolors permanently.

Dew (which usually forms on windows and in cold corners and drips down from there), can do the same harm.

This is why you have to periodically vent your house when using a swamp cooler. It’s not because of the humidity in your air, but to prevent dew formation when it gets cold outside!

Vent your room periodically instead

Let’s take an example to illustrate this. Imagine you’ve been running your swamp cooler throughout a hot day. By evening, the humidity level in your house has increased due to the evaporative cooling process.

As the night approaches and temperatures drop, the chances of reaching the dew point inside your house rise.

To prevent this, you need to vent your house before the temperature starts to fall. This could be as simple as opening a window or door for a short time (10 minutes) to let out the humid air.

Once the humidity levels drop, you can close your windows and continue using the swamp cooler.

While venting, you can continue running your swamp cooler. I recommend venting for 10 minutes every 3-4 hours.

The best way to track indoor humidity is to use a hygrometer, such as this one (click here to view it on amazon).

I like to vent my room until the indoor humidity is within a range of 10% of the outdoor humidity.

Any venting beyond that (to match outdoor humidity) gives you diminishing returns and will take a very long time.

Myth #2: The longer a Swamp Cooler runs, the more humidity builds up

Let’s start with the facts. Contrary to common belief, swamp coolers don’t magically pump unlimited moisture into your room, making it feel like a tropical rainforest.

What happens, in reality, is based on a simple principle of evaporation. Your room’s temperature determines the total amount of water it can accommodate in vapor form.

Humidity limit at room temperature

Picture this. Your room’s temperature hovers around 72°F (22°C). Now, it has the capacity to hold up to about 19 grams of water per cubic meter.

No matter how long you keep your swamp cooler running, it can’t force more water vapor into the air than this limit.

So, in principle, you can run your swamp cooler 24/7.

A fan can not evaporate water beyond the physical limit

The fan in your swamp cooler, you ask? It’s not there to break any laws of physics and push in more water vapor.

Its job is simply to speed up the cooling process by aiding the evaporation.

This helps the room reach its humidity limit faster, but it doesn’t push it over the edge.

Once your room reaches this humidity ceiling (which depends on the temperature), your swamp cooler changes its role.

It transitions from being a humidity adder to simply an air mover. It’s akin to reaching a saturation point – beyond this, the swamp cooler doesn’t add extra humidity, it just circulates the air.

Myth #3: Open windows increase airflow and Swamp Cooler efficiency

The myth here goes something like this: keeping a window open will draw air through the swamp cooler, aiding the airflow, and ultimately making the cooling more effective.

Note: This myth does not affect portable swamp coolers, since they stand in the middle of your room and are not exposed to the outside. With a portable swamp cooler this myth would make even less sense.

But let’s take a closer look at this:

Roof and window swamp coolers suck in outdoor air

Swamp coolers, especially the ones mounted on windows or roofs, suck in hot air from the outside. Having an open window on the opposite side of the house might sound like a smart move to improve airflow, but that’s not always the case.

You can’t influence outdoor airflow direction

One factor that many overlook is the unpredictable nature of airflow. When you leave a window open, there’s no guarantee that the airflow will move in the direction you’d like. The airflow, governed by weather factors like wind direction, temperature gradients, and even the design of your home, can act in surprising ways.

The following scenario can happen:

Outside air can enter through the window, pass through your swamp cooler, and escape out. In this case, you cool the outside while your indoor temperature rises!

That’s the exact opposite of what you’d want.

Airflow through window affects swamp cooler fan efficiency

Another factor to consider is the effect of outdoor airflow on the swamp cooler’s fan. If the wind direction outside happens to be opposite to the fan’s blowing direction, it can hamper the fan’s ability to circulate air inside the room, making your swamp cooler less efficient.

To wrap it up, the idea that open windows can boost your swamp cooler’s efficiency doesn’t hold.

It’s better to stick to regular venting and avoid any unnecessary rise in indoor temperature that might result from an open window.

After all, the ultimate goal is to enjoy a cool, comfortable indoor environment, not to air-condition the outdoors.


Wrapping up, you don’t need to keep your windows open for your swamp cooler to do its job.

It’s all about managing the indoor humidity smartly and not about inviting in the outside air all the time.

Vent your rooms every once in a while and use fans or open doors inside your house for better air circulation.

You control your cooler, not the other way around. So, enjoy a chilled summer without fussing over open windows.