Do Portable Air Conditioners need to be Vented?

Do all portable air conditioners need to be vented? If so, why do all air conditioners need a hose? And can you use a portable AC without a hose?

Quick answer: Yes, all portable air conditioners need to be vented. The heat extracted from the air has to leave your room, otherwise, it will mix up with the cold air again. Ventless ACs are a marketing scam and never work.

Let’s have a closer look.

Why do portable air conditioners need to be vented?

First of all, the main point of a portable air conditioner is to reduce the temperature in your room. An AC does that by blowing out cold air. Simple, right?

But where does the cold air come from? The cold air is the air from your room but without the heat. 

The heat is extracted in a cooling process similar to a refrigerator’s. A compressed liquid refrigerant evaporates to gas due to the hot air in your room. The from your room is converted to another form of energy, stored in the gas.

This causes the amount of heat in your room to decrease.

Then, the gaseous refrigerant goes through a duct system to another part of the AC where a compressor compresses it to a liquid again. The compressing releases the heat energy from the refrigerant again.

That’s where it gets interesting. Let’s see what happens when your portable air conditioner does have a hose attached. 

On the back side, the portable AC vents the heat.

Cold air comes out of the front of the AC, while hot air leaves on the back.

It takes only a short time until the hot and cold air mix up again. And we are back where we started.

And it gets even worse than that: 

Because the compressor and the fans are moving parts, they create friction. That friction results in additional heat being released.

So, leaving a portable air conditioner running without venting the hot air is actually worse than not running a portable AC at all.

There’s even a law in physics describing exactly this: The second law of thermodynamics. It states that the entropy in a closed system always increases. 

It took me a while to grasp that concept in engineering class, but here’s the law in simpler terms, applied to the air streams of an air conditioner:

“Due to the second law of thermodynamics, the hot stream is heated by more than the cool stream is cooled. So mixing the two together will result in a net heating effect”

Solandri on

So how do we fix this? You use a hose to blow the extracted heat out the window. This way, the cold air stays in your room, while the hot air leaves.

How to vent a portable air conditioner

Now that you know why you always have to vent a portable air conditioner, let’s look at the best way to do that.

Vent heat out the window

First of all, the most popular choice for most people is to vent the hot air out the window. All “real” portable air conditioners come with a hose and some additional parts to fixate this hose to an opening in the window.

Vent into another room

Alternatively, it is also possible to vent the heat into another room, such as a bathroom, where you don’t care about the temperature. However, depending on the insulation between the rooms the heat will re-enter your room more or less fast. It depends on the material of your doors, the size of the door gaps, etc.

Also, venting the heat to a neighboring room could, in the long run, damage furniture, wooden floors, and wooden ceilings as they are all sensitive to high temperature and moisture. Ideally, the neighboring room you vent the heat into, should, therefore, have an open window.

I suggest venting into another room only for short periods of time in the high summer heat. Any venting longer than a few weeks in a row will likely wear down the room noticeably.

Vent out the chimney

A third option is to vent a portable air conditioner through a fireplace or oven. Since these are connected to your chimney, which, in turn, is an opening to the outside, venting air conditioner heat through a chimney is technically the same as venting through a window.

The only difference is that the airways are longer and therefore, because of the chimney effect, there will be a higher suction force pulling in more heat from other rooms into your room.

Also, venting out the chimney will likely pollute your air conditioner’s hose. And, in the winter months, when you use your fireplace to heat, there’s a risk of fire when you insert the air conditioner hose. But I guess you won’t use an air conditioner in winter, so that’s just a theoretical issue.

You probably agree that you should vent your portable air conditioner out the window. It is the best option of all 3 and has no negative side effects.

Proper venting saves money and increases cooling efficiency

You can maximize your portable air conditioner’s cooling efficiency by venting it properly. Here’s how:

First of all, if your portable air conditioner came with a junk-quality window kit, then I’d suggest looking for a better one. A good window kit helps with insulation by using better materials and by not leaving any air gaps.

Also, you can insulate the exhaust hose using a hose insulation kit. This prevents heat from re-entering the room while it’s on its way out.

To insulate your portable AC hose, I recommend this insulation wrap (click here to view it on amazon).

Also, ensure that there are no holes in your portable air conditioner’s hose. If you find any, fix them using this HVAC tape (click to view it on amazon) (regular duct tape is fine as well).

Additionally, ensure that you position your portable air conditioner properly. Ensure that the air easily flows out of the window by checking that there are no kinks in the hose.

The less work the AC fans have to do, the less air movement is involved in cooling and the less air re-enters your room through door gaps. That’s one of the reasons window ACs are more efficient than portable ACs: They cause less air movement.

Are there portable air conditioners that do not need to be vented?

When you are looking to buy portable air conditioners online, you will find tons of “ventless” portable air conditioners. Why would you even pick a portable air conditioner with a hose if you can pick a model without one?

As we’ve already seen, any ACs without an exhaust to the outside of your room is a scam product. They don’t work physically.

They might extract the heat for a short time. But within a few seconds or minutes the cold air and the hot air mix again.

If you ever see a portable AC without a hose, you immediately know, it’s a scam product.


All portable air conditioners need to be vented! There’s no way around it. If you use your portable AC without venting the heat outdoors, you will even get a net heating effect.

So, it’s pointless to use a portable air conditioner without venting the air.