What Is a Portable AC Unit?

Most people are quite familiar with window AC units, the little metal boxes with backs covered in shiny metal fins that appear in windows across the country every summer when the temperatures rise. They were invented way back in 1931 and, by the 1950s, had become commonplace.

Portable AC units are a more recent addition to the market. Instead of a window mount design, they have a free-standing design similar, in appearance, to a large dehumidifier. The units feature either a single or dual hose exhaust which is vented to a nearby window (or any available opening) by a flexible duct.

Most units come with all the accessories you need (flexible hose, plastic slider plate to fit in a standard window, etc.) to get started. Prices typically range from around $300-700 with portable AC units on the higher end of the price scale offering more cooling power and features that increase efficiency.

If You Can Use a Window Unit, Skip the Portable AC

Before we even dig into portable air conditioner tips, let’s be very upfront to save the folks doing pre-purchase research time and money.

If you can use a regular old-fashioned window unit in your home, from a cost and efficiency standpoint, you really can’t beat them. They cost less initially and offer more cooling power per dollar spent, and their operational cost over time is lower.

You can pick up a very basic model for under $200 to cool a small room, or even larger units for around $400-500 to cool bigger rooms or even small homes.

But we understand that not everyone can use a window unit. Maybe your home only has casement windows so you can’t mount a window unit in them. Maybe your local Home Owner’s Association or condo rules restrict you from putting anything in the window.

Or maybe the building rules or local ordinances prevent you from using one. It’s common for high-rise buildings to have rules against window units for safety purposes—which is fair, as a 80-100 pound block of metal plummeting off a high-rise is quite a safety hazard.

If you’re in a situation where a window AC unit just won’t work for your situation, keep reading as we break down the basics of shopping for a portable AC unit and using it effectively.

Single Hose vs. Dual Hose: Always Buy Dual

If you have already done some reading on portable air conditioners, one thing you’ve likely come across is heavy criticism of the efficiency of said units.

This criticism is well earned, and most of it has to do with how inefficiently single-hose units operate. To understand why they’re so inefficient, let’s first talk about how window units, mini-split units, and even whole house AC units work.

These systems have two “loops,” if you will, for the two different functions required to cool your space and get rid of the heat inside it. The first loop passes air from your home over cooling coils and back out into your home. The second loop, on the other side of the system, releases that heat outside your home. The air in your home isn’t used to blow the hot air outside, the two loops stay completely separate: the AC cools the interior air again and again in a loop, and outside your home the AC unit releases heat in a separate loop.

Dual-hose units emulate that traditional method by pulling in air from outside your home, blowing it over condenser coils, and shooting the heat from the AC unit out the other hose. It’s not perfect because some of the heat is going to radiate from the flexible intake and exhaust hoses back into your room, but it’s much better than the single-hose design.

What’s so bad about the single-hose design? It uses one exhaust hose to eject the heat. This creates a negative pressure exactly as if you’d put a fan in your window. What happens when you put a fan in your window? It creates a draft from other places in your home. You can shoot air out a window without replacing that air from somewhere else.

So, where a regular air conditioner or even a dual-hose portable unit is constantly pulling in air from the room, cooling it, and returning it, all while maintaining balanced air pressure in the room, a single-hose system is constantly lowering the pressure in the room and drawing unconditioned air from outside the room through any ingress points—under the door, unsealed outlets or window frames, etc.

The end result is that while the single-hose AC unit might make you feel cool if you’re standing right in front of it, and the room will be a little cooler overall, it’ll never feel as cool and dry as it would with a dual-hose AC unit or window unit—because it is constantly pulling hot air from outside the room. It’s more or less like running your AC unit with a window open.

How to Use a Portable AC Unit Efficiently

With a little background about portable AC units and some buying tips out of the way, let’s look at how to get the most value out of your unit.

Minimize Exhaust Hose Distance

Just because your unit comes with hoses that can be stretched out up-to-X feet, doesn’t mean you should use all X feet.

The shorter and straighter the distance the hose has to travel to the window, the better. Don’t balance the unit precariously on a side table or anything in service of using the absolute minimum distance, but do position it so that the hose is as short as possible.

If you are using the window adapter in a vertical position with a dual-hose system, put the coil exhaust hose on the top (and the intake hose on the bottom). This will help your unit work more efficiently by venting hot air upwards and pulling in cooler air from below, and every bit helps!

Use the Correct Window Adapter

If you have a very standard single or double-hung window, then there’s a good chance the window adapter that came with your portable AC unit will fit just fine in your window. The only extra consideration would be to use some weather stripping or tape to seal any gaps around the edges.

But if you have anything other than a standard hung window, you’ll need a different type of adapter. You can cobble your own together with the materials you have around the house in a pinch, but you might prefer to have something a little better-looking and custom-made for the task.

If you want to vent out of a sliding glass door, you’ll need a very tall vertical adapter. If you have a casement window, then you’ll need a flexible fabric adapter that you can stretch over the window.

When ordering an adapter, make sure you take into account the following things so you’re not stuck with an adapter that doesn’t fit your AC unit or window:

Match the adapter diameter to your unit. Hoses typically come in 5. 1″ or 5. 9″ diameters. The actual window kit might have a round or an oval hole (if it has an oval hole, it should come with a small adapter for your round hose). Measure the window size carefully. If your sliding glass door opening is 87″ tall, but the adapter can only be extended to 70″, you’ll be over a foot short.

Minimize Heat Sources

Portable AC units are not as powerful as window units or mini-split systems. Everything you can do to minimize heat gains and heat introduction to the area you are cooling is ideal.

Keep the drapes drawn on the sunny side of the room. Don’t run your beefy gaming computer unless you’re actively playing a game, and consider using your phone or tablet for casual web browsing—computers add as much heat to a room as a space heater.

Leave the Unit Running

It might be tempting to turn the unit off when you’re at work or otherwise away from home. While that’s certainly an energy (and budget) conscious thing to do, you’ll end up with an even cruddier performance from the portable AC unit when you’re home and trying to stay cool.

When cooling your home, you’re not just cooling the air. You’re also cooling the contents of the home. That includes every piece of furniture, every book on your bookshelf, the clothes in your closet, and the very structure around you.

If you come home after work and your home has been baking in the sun all day, your little portable AC unit is going to struggle for the rest of the evening and well into the night to extract heat and properly cool the place.

It’s a lot more efficient to remove heat at night and then run the system all day to manage the heat than it is to wait until every square inch of the space is hot. Supercooling concepts apply to air conditioners of all sizes, not just whole house AC units.

Keep Your Filters Clean and Watch for Water Buildup

Your portable AC unit likely has an air filter that prevents large bits of dust, pet fur, and such from getting directly to the coils. You need to routinely check this filter (or directly inspect the coils if your unit doesn’t have a filter) for optimal operation.

Not only will a dirty filter decrease the efficiency of your unit, but if you let it go too long, you can run into more serious problems like your coils icing over or the unit burning out.

On top of that, be aware of the kind of portable AC unit you have and how it deals with moisture. Many models are what is known as “fully evaporative,” which means the moisture the unit pulls from the air is ejected from your home along with the warm air in the exhaust hose.

Some units are only partially evaporative and you’ll need to empty the unit just like you would empty a dehumidifier (by pulling the bucket out and dumping it down the drain). Others, more rarely, have a drain hose with a pump that you run out the same window as the exhaust vent.

Even if you have a fully evaporative unit, very humid weather may necessitate manually draining the unit using a small drain plug located at the base of the model.

Consider Jerryrigging a Second Hose

We don’t recommend this course of action if you’re unwilling to proceed carefully and with the understanding that you may damage your portable AC unit if you misstep. If you have even the slightest concern that you don’t know what you’re doing, and won’t be able to find the right fire-safe materials to roll your own exhaust adapter or such, then we advise against it entirely.

But if you’re willing to do a little MacGyver work and you’re confident in your ability to do so safely, adding a second hose to turn your single-hose model into a dual-hose model will offer a significant increase in efficiency. (Do check if your particular model has a dual-hose adapter kit. It’s rare, but some companies like GE offer kits for some of their portable AC units.)

You’ll need to carefully inspect the model you have and determine where the condenser air intake is. Remember there are two “loops” in every air conditioner. One loop pulls air in from room, cools it, and ejects it into the room. One loop pulls in air to cool the condenser coils and then ejects that hot air from the room. On a single-hose unit, there will be two intakes on the unit—one to pull in air and push cold air into the room, and one to pull in air and push it out the hose.

Your goal is to locate the vent that is pulling air into the condenser. Checking the diagrams in the manual can help, as well as carefully inspecting the unit while it is operating.

It might help to see a side-by-side example of what we’re talking about. Above, we have two examples of portable AC units from the same company, Hisense, side-by-side. The lefthand unit features a dual-hose design.

Fresh air comes in on the left, and hot air is ejected through the hose on the right. The single-hose model, seen on the left, has the same design, except the fresh air is pulled from the room via the air intake grill on the left-hand side of the machine. If you were to duct that vent out the window with a second hose, you’d get the benefits of a dual-hose system.

Once you think you’ve located the air intake, confirm it by running the unit and using a piece of paper (or another very light object like tissue paper, plastic cling wrap, etc.) to cover that area of the machine briefly. If the machine is sucking in air the piece of paper should stick.

You can further confirm it’s the correct intake by checking which exhaust loop decreases in strength when you cover that vent. If it’s the room loop, the fan blowing out the top of the unit should struggle when you cover the vent. If it’s the exhaust vent intake, then the hot air blowing out the back will slow down when you briefly cover the vent.

Now all you need to do is construct a box of some sort that is an appropriate size to cover the vent, cut a hole in the box that matches the diameter of your second vent hose, specially purchased for the purpose, and run that vent hose to window the original single-hose is connected to (again, you may need to buy, or make, a new window adapter).

Run the system and monitor it for any malfunctioning, overheating, or other problems. If you’ve jerryrigged the whole thing properly, you’ll notice two things immediately. First, there won’t be a draft under the door of the room you’re using the portable unit in any longer (because it’s pulling the air it needs from outside). And second, the room will cool much faster, again, because it’s not pulling huge amounts of unconditioned air from outside the room.

We want to strongly emphasize, again, however, that this is a bit of Macgyvering best suited for people confident in their ability to do so safely. When in doubt, just buy a unit that comes with the dual-hose design right out of the box.