Portable Air Conditioners and How They Work

For spot cooling and keeping costs down, portable air conditioners are a great idea when it's uneconomical to have a fixed unit in a room or other open space.

There are several benefits to choosing this option and in this category part of the site, I'll be delving into the pros and cons as well as taking individual aspects of these units and presenting them in greater detail in separate articles.

If you are in the situation where you maybe can't afford to have an AC system installed in your home, buying a smaller, free standing air conditioner unit can be beneficial. This is because it will provide you with some respite from the heat of summer while not costing you as much as a larger fixed unit or system would.

portable air conditionersTo give you an overview of these appliances, I'll introduce the concept to you here but if you need more information, take a look at the more detailed articles titles listed at the foot of this overview.

I have created this guide to help you have a good understanding of how a portable air conditioner works and how it cools a room in your house.

If you're interested in finding out which air conditioners are best for you, take a look to my guide on portable air conditioners.

Let's now take a look at how portable AC units operate and how they cool things down to provide you with a comfortable indoor climate during hot weather.

How Do Portable Air Conditioners Work?

The cycle that a portable air conditioner goes through starts as it pulls hot, moist air from the room, then cools and dries it inside the unit. The resulting chilled air is then circulated throughout the room.

The unwanted warm air and excess moisture is finally exhausted out of the window through a flexible hose.

From this process, it is fairly clear that a portable air conditioner's main function is to remove heat from the air in a space and transfer it to the outside.

A portable conditioner contains three essential components in order to make this process work.

These three components are combined to create the working process inside a portable air conditioner. Here's that process in some more detail:

  1. The spinning fan draws hot, humid air from the indoor space inside the unit.
  2. The condenser coils cool the hot air inside the unit. Water vapor is condensed on the coils, effectively extracting moisture from humid air.
  3. In the coils, the air's heat transfers to the refrigerant, causing it to heat up and transform into a high-pressure gas, moving throughout the air conditioner's system.
  4. Two ways to get rid of the moisture in the air are available: either through a self-evaporation process that exhausts water vapor outside, or by collecting it inside a container the user must manually empty periodically.
  5. The compressor continually compresses the refrigerant during the whole process. Heat is generated by these components and that must also be vented outside through the exhaust hose that all portable air conditioners must have connected to an outlet either though a window or wall vent.

An important point is that the refrigerant will become less able to absorb the heat from indoor air as the condenser coils become dirty. This situation could mean the compressor has to work harder, leading to potential overheating and the unit shutting down.

You may be interested to know that all AC units work the same way. A portable air conditioner contains all the necessary components to be used as a stand-alone cooling device.

You can compare this to a central air or ductless air conditioner system made up of two separate units: an evaporator located indoors that disperses cool air into the room and a compressor located outdoors that cycles the refrigerant.

Portable Air Conditioners: Single Hose vs Dual Hose

Now you know how portable air conditioners cool down rooms. One of those steps is to let the hot air out from inside the unit though its vent hose.

If you take a look at the back of a portable air conditioner unit, you'll see there is either one or two vent holes that can be connected to one or two vent hoses, depending on the model.

Most portable AC models will have one exhaust vent hose. With this set up, air is drawn into the unit from the room to be cooled down, with the unwanted hot, moist air being exhausted out through the hose to the outside.

This works fairly well, although it can create some negative pressure in the room because some of the internal air is being removed. I'll talk more about that in a moment.

A portable AC model with two hoses that can be connected to the back of the unit has some advantages over a single-hose model.

With dual-hose models, one hose brings in fresh air from outside which is cooled inside the unit by its refrigeration process. The second hose is used to exhaust the unwanted hot, moist air to the outside.

Dual hose portable AC conditioners, thanks to this design, don't create any negative pressure inside as do single-hose units.

Negative Indoor Pressure

I want to make a point about the creation of negative pressure indoors, as is a trait of single-hose portable units.

When the air pressure inside a room is lower than the pressure outside, nature works to restore the balance. That happens by hot air being drawn in from outside to balance the air pressure.

No matter how well sealed you believe your home to be, if there is a negative pressure inside, hot, outside air will find a way to get in a restore the same pressure as outside.

This means there is more hot air for the AC to deal with, forcing it to work harder to maintain a stable indoor temperature. This cause greater energy use, lowering efficiency and ultimately costing you more when your next electricity bill arrives!

Dual hose portable AC models eliminate this problem by having the air intake coming from outside air, so the indoor and outdoor pressure balance is always maintained. That means dual hose models tend to be more efficient and therefore more economical when it comes to using energy to keep you cool, ultimately saving money on that next electricity bill!

Can a Portable Air Conditioner Hose be Extended?

It is not a good idea to extend the length of your portable air conditioner's hose more than the manufacturer's guidelines indicate.

The appliance will work at its peak efficiently if the hose length is within the manufacturer's stated extension limit. The flexible hose that comes with the unit is designed to be pulled out to extend it to its natural full length if needed.

Extend the hose beyond this limit (for example adding an extra length of hose to the end and sealing it with duct take) could cause overheating. Also beware that this can invalidate the manufacturer's warranty.

Exhaust Hose Venting

Questions sometimes pop up about how best to vent a portable air conditioner. A window is the most common place to vent an exhaust hose, using the supplied window venting kit that is generally designed to fit traditional-sized windows.

Using a sliding glass door can prove to be more difficult and complicated than a window, although with some ingenuity and handyman skill, this can be achieved.

Standard window kits are generally too short for sliding glass doors to be extended to the full height, However, if you want to vent your portable air conditioner through a sliding glass door opening, there are options:

  1. If a special extension kit is available from the manufacturer, purchase and use it
  2. Cover the open area with plywood or styrofoam that you cut to size yourself

Whatever installation route you choose to take, be sure to read the owner's manual and follow the instructions.

Does Water Need to be Drained from a Portable Air Conditioner?

Most portable air conditioner models require water to be drained periodically, as it is quite common for a portable AC to fill with water often over the course of it operating in hot weather.

There are a number of ways it can be done.

As already covered here, one function of a portable conditioner is to remove moisture from humid air as it is cooled. Below are some ways a portable air conditioners deals with moisture and condensation.

Fully Self-Evaporative Portable AC Model

Portable air conditioners that are self-evaporative work to remove moisture by internally re-evaporating it then exhausting it through the vent hose along with the unwanted hot air.

This makes them more convenient, since it saves you the hassle of emptying any water that would otherwise collect an internal container. See my fully detailed article on self evaporating portable air conditioner units.

Because it requires very little maintenance, this type of auto-evaporative portable AC model is rapidly growing in popularity.

Gravity Drain

Most portable air conditioners with or without condensate pump can have collected water removed by attaching a drain hose.

Drain hoses are usually included with most portable ACs. The water is pulled by gravity to drain outside the unit, as the name implies. This method works by connecting the hose to your unit and routing the other end to a handy floor drain or other convenient outflow route.

Alternatively, a condensate pump can be attached to the drain hose if there is no floor drain available, or if you want to move the water to another place.

The condensate pump draws the water from the device pumping it upwards, so you can empty the water into a sink or into a bucket.

Water Collection Container

If your AC has a removable internal collection container or tank, this provides you with another option to remove water from your unit.

The moisture from the air will build up over time and will eventually be deposited in the tank. You will need to empty it when it becomes full.

This step is easy: Turn the portable air conditioner on, then take out the bucket and pour the water into a sink.

To get it working again, you will need to replace the bucket in the AC unit.

Portable Air Conditioner Requirements

Although different models of portable air conditioners may have different requirements, most are simple enough to set up.

A portable AC unit's purpose is to cool down a space and reduce humidity. These are the requirements for this to work:

Air conditioners use considerable amounts of energy to perform their task, as you likely know. It is a good idea to use a separate electricity circuit for high-energy devices to avoid overloading others.

The portable air conditioner owner's guide contains additional information about your brand and model.

Portable AC Units Used in Multiple Rooms

You may be able cool multiple rooms depending on the size and power output of your AC unit.

These machines work in a similar way as a window conditioner to cool an area as needed. However, cold air cannot travel along long hallways or throughout larger areas than the unit is rated to cool.

It may be possible to cool two rooms connected by a large opening. However, the cool air may not be evenly distributed.

The distance between the rooms and their sizes along with the output rating of the AC unit will determine how well a portable air conditioner will work in this setup. Ensure the rooms are connected to allow cold air to flow through them.

A small unit will work well in small spaces. You might be able even to use a different type of air cooler such as an evaporative cooler (swamp cooler) if the humidity level is low enough.

Are Portable AC Units a Good Choice?

For those who fall within any of these categories, portable air conditioners can be a great option, if you need:

If one of more of the above scenarios apply to you, a portable air conditioner is a great consideration to cool your apartment or home. They are also an excellent choice for those who need more control than a window-mounted AC unit.

Does a Portable Air Conditioner Work Without a Window?

Connecting to a window is the best way to vent a portable air conditioner to expel the unit's hot air.

While a portable air conditioner's hot air must be exhausted from a room, it does not necessarily need to be vented through a window.

You could instead vent the hose through an opening in an external wall, through a drop ceiling as in the case of commercial portable air conditioners, up a chimney or to an existing dryer vent leading to the outside.

So yes, a portable air conditioner will work without a window as long as there is an alternative external venting method available that you can use with some modifying it to make it work effectively.

Should You Put Water in a Portable Air Conditioner?

You should not put water in portable air conditioners that use an exhaust hose. They work by extracting moisture from the air and expelling it outside through the exhaust vent.

They are not designed to take water.

However, a "ventless air conditioner" is another type of portable cooling unit, more correctly called an evaporative cooler or swamp cooler. These units do require water to be used.

Swamp coolers work by using a fan to evaporate water through a soaked medium connected to a water tank, chilling the air and pushing it into the room. They do not use a refrigeration process and are therefore NOT true air conditioners.

Why Are Portable Air Conditioners Bad?

Portable air conditioners are sometimes viewed as a poor deal, because of some imperfections and issues with the way they work.

A portable air conditioner can be considered bad, especially in small homes and apartments because it takes up floor space. It cannot be installed in a window opening but it has to be placed next to it in order to connect the vent hose.

Portable air conditioners can also be considered noisy. The fan will continue to work even if the unit is not cooling a space. These units don't shut off like window air conditioners.

People don't like that portable air conditioners can only cool down one room. Only central air conditioning systems have this capability, however.

Portable AC units are generally less efficient than other AC units, making them are more expensive to run than other AC options of comparable output rating.

Common Portable Air Conditioner Features

You may be curious about the features of portable air conditioners, now that you are aware how they work and where they work best.

While certain features can vary based on brand and model, here are some commonly found options on new portable units.

Portable Air Conditioner Maintenance

These are some basic maintenance tips to help your portable air conditioner last longer.

Every two weeks, clean the filter. This filter will become clogged if it is contaminated with dirt and other debris. Use warm water and mild dishwashing detergent to clean the filter. Next, rinse the filter well and shake off any excess water. Before putting the filter back in the air conditioner, always let it dry completely.

Regularly clean the grill of your air vent to remove any hair particles trapped in it. Use a mild dishwashing detergent and a damp, lint free cloth to clean the exterior. To avoid fire or shock, unplug your portable air conditioner before you perform this maintenance step.

To prevent mold growth, empty the water collection tray or bucket every week if your unit is not self-evaporating. This tray should be cleaned before you store the unit. The AC unit should be stored in a dry, cool place. You can cover it with a sheet, or you can return it to the original carton.

Pros and Cons of Portable AC

As with most things, there are pros and cons to owning and using a portable air conditioning unit instead of opting for a larger, fixed cooling installation.


Easily the most obvious one of these is the cost of purchasing such an appliance compared to the greater cost of a fixed system. When you don't have a lot of money in your pocket, or your credit card is getting perilously close to its limit but you really, really need some way to get cool in the heat and you find you can get one of these for maybe under three hundred bucks, it looks like a no brainer.

For cooling small rooms, a portable or free standing air conditioner is often the best option because it will make the room cool pretty fast without using too much power, so running costs are affordable in this situation. It's when room sizes get bigger that the balance starts to tip in the wrong direction, as you will see below!

Also the idea of portability is a good one especially if you can only afford to buy a single machine. At least you can wheel it to whichever room you're occupying and that can be a big cost saving in not needing a fixed unit in every room.

Another big pro is that because you only have the one unit running and using power, that's all you're paying for. All too often having fixed units in every room means one or more invariably get left running when no one is in there, wasting power and costing you more money than it needs to!


While these machines are labelled as being "portable", there are one or two details that kind of cast a doubt over just how moveable they really are. The first glaringly obvious one is the ugly plastic expandable hose (or dual hoses) that comes with the unit which you notice when you take it out of its box for the first time.

portable air conditionerYou might not have paid any heed to the guy that sold it to you in the store when he was explaining about venting the unit to the outside, or maybe you bought it online and didn't read all the information on the page. But there it is. That at first strange addition that you may not have been expecting to see!

Now you discover you have to hook that hose up to the back of the AC unit and then fix it to a venting kit you also have to install on a window in the room you're going to use it in. That means you can't just wheel it from room to room without unhooking the hose from its window and hooking it up to another window in another room!

Power Consumption

OK, you get over the exhaust hose thing that is probably the biggest irritation to owners or buyers of portable air conditioners. The next downside is the running cost.

Sure, on the low setting it doesn't seem to be using so much power. Maybe it's glugging a kilowatt or so, which seems a lot but for the relief from the heat, you'll manage it.

But when the low setting isn't cutting it, you need to turn it up and now on the high setting it's draining 1.5 to 2 kilowatts or more. If you were to go look at your electricity meter, you'd see the numbers flying in an upward direction very fast indeed!

But that's not just a trait of portables. Fixed and window AC units also use a lot of power when you crank them up high.

Of course, there are cheaper to run alternative coolers, such as the so-called ventless air conditioners (they are explained in that article), which are really evaporative coolers (swamp coolers) and they don't have an exhaust vent hose either.

Do You Want More Information?

Of course, I could go on at length about the ups and downs of self contained free standing AC devices, but this article is focused on the main pros and cons of this particular type of cooler as an overview. There are more detailed articles associated with this in this section on air conditioning (click that link) where you can learn more if you want to.


I hope you found the information helpful in answering your questions about portable air conditioners and how they work in cooling down a room.

These useful and compact units have a number of internal components that extract hot air from a room while providing cool air in its place. They also have various methods to remove collected moisture.

Although there are many different types from regular to WiFi ready smart portable AC unit brands and models, they all work in much the same way to maintain a comfortable indoor climate for you and your family to enjoy during hot weather.

Last Updated: August 29, 2021

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