How Do Portable Air Conditioners Work? Basic Principles + Tips

Portable air conditioners are, above all, easy to use and effective. In most aspects, the inner workings of the portable air conditioners are similar to that of a standard refrigerator.

Portable AC units are much easier to install than any other AC unit (prepared right out of the box). Obviously, they have a much greater effect on air conditioning than simple fans as well.

Two main tasks portable air conditioners are well equipped for are:

  1. Cooling down one or several rooms (primary function).
  2. Removing the humidity out of the indoor air (dehumidification is a secondary function).

We will look at how the portable air conditioners lower the room temperature and dehumidify the air. As far as dehumidification is concerned, there are major differences between the units (self-evaporation, gravity-drain, or manual removal of water).

We’ll also look at the differences in how single-hose and double-hose portable AC units operate.

On top of that, you can also check out the best and most energy-efficient portable AC units here.

Basic Cooling And Dehumidification Principle Of Every Portable Air Conditioner

Everyone will tell you that installing a portable air condition relatively easy. Unbox the unit, plugin it in, install the exhaust hose (similar to tumble dryer hose) out of the window and turn it on.

If you don’t have 15,000+ BTU portable AC unit, the standard 115/120 V power grid will more than suffice. It’s also worth mentioning that the smallest portable AC units have capacity of 8,000 BTU.

Nonetheless, the thermodynamic principles behind the AC units are very much the same as with all other air conditioners.

The goal is to extract the heat out of a room (or two, depending on the size) and transfer that heat outdoors. That’s why every portable conditioner has 3 key components:

  1. Refrigerant (to cool the air).
  2. Compressor (to compress the refrigerant).
  3. Fan (to move the air).

Every portable air conditioner operates based on the refrigeration cycle. Here is a quick sketch of how the refrigeration cycle looks in theory:

sketch of a refrigeration cycle on which the way portable air conditioner principles are based on

This is the most basic sense of how a portable air conditioner works:

  1. The fan sucks the hot and humid air from the indoor room inside the portable air conditioner.
  2. Inside the unit, the hot and humid air is cooled down by condensing on cold coils. This cools down the air and extracts the moisture (air moisture condenses on the coils). This is where the heat from the air is transferred to the refrigerant in the coils. That turns the refrigerant fluid into a gas; that’s why these are ‘evaporator coils’.
  3. The cool air is vented back into the room.
  4. The moisture from the air is gathered and can be vented outside or you have to manually remove the bucket.
  5. The refrigerant in gas form is compressed by the compressor on the so-called ‘condenser coils’. The heat that is released by this process is vented out of the exhaust vent installed through the window/sliding door.
  6. This cycle goes on and on.

There are two slightly different approaches when it comes to how portable AC units work. You have a single-hose and two-hose units. They are both based on the same principle, but the airflow is a bit different.

Single-Hose Portable AC Unit

Single-hose portable air conditioners are the most common ones. On average, they are also cheaper than double-hose AC units.

They have a single hose; usually installed through a window, or even through a wall. That hose only has one purpose: to serve as an exhaust vent for the hot air.

In essence, the single-hose portable air conditioner sucks in the hot room air and vents it outdoors via a single hose.

While this is the simplest way of how a portable air conditioner operates, you can obviously see that the single-hose AC unit literally sucks the air out of a room without replacing it.

The consequence of that is the lower pressure in the room. You won’t feel it in your eardrums; the fall in air pressure in not so severe.

However, the lower pressure will have to be offset in some way. In practice, the air from other rooms will be sucked in the room in which a single-hose portable air conditioner is operating.

The simple advice for a single-hose portable AC unit is to limit access to other hot air. Practically, that means you should close the door in the room where the unit is operated.

Double-Hose Portable AC Unit

Double-hose portable air conditioners are less common, more difficult to install, and more expensive. However, they can achieve higher energy-efficiency rating (EER rating) and replace indoor air with fresh outdoor air.

The way a double-hose portable air conditioner works is by using:

  1. First hose to bring the fresh air in from the outside.
  2. Second hose to vent the hot indoor air out (the single-hose portable AC units only have this one).

By having one hose to bring the air indoors, you don’t experience that lower pressure the single-hose portable AC units might cause. That means that the air is better conditioned inside the room where the double-hose unit is located.

On top of that, you get the additional benefits when operating a dual-hose portable AC unit:

  1. Higher energy efficiency. Because the unit doesn’t have to work against low pressure, the EER rating of dual-hose portable AC units can be above 10.
  2. Quicker cooling. Obviously, two hoses can condition the air much faster than a single hose.

What is surprising, however, is that you don’t see that many double-hose units. The main reason is probably that they are much more complex to make. Nonetheless, the higher EER rating makes it much more eco-friendly than the single-hose units and you can use fresh outdoor air.

For example, the Whynter ARC-14S (#1 pick) is one of the best, if not the best, dual-hose portable air conditioner.

whynter is the portable air conditioner with the highest eer rating making it the most energy efficient
Whynter ARC-14S has two vents. One to suck the air in, and the other to flush the hot air out.

With the EER rating of 11.20, it is also the most energy-efficient portable air conditioner you can find.

3 Ways Of How To Remove Moisture Portable Air Conditioners Collect

The biggest difference between how portable air conditioners work is the way of how you remove the water from the unit itself.

In fact, most of the people who are in the market for a portable air conditioner don’t exactly need a dehumidification unit. Nonetheless, all portable air conditioners are dehumidifiers. Removing moisture out of the air is the side-effect of cooling the air down.

What is more, dehumidification is something that is actually quite advantageous. Here are 3 reasons why:

  1. Summer air is humid. Too much humidity boosts mold and mildew growth.
  2. It’s easier to breathe if air is not humid.
  3. The higher the relative humidity of the air, the lower is the energy-effectiveness of portable AC units.

Portable AC units do a very good job as dehumidifiers. A single unit can remove more than 30 pints of water every day.

However, that water has to go somewhere. The key part of how portable AC units work is connected to the way they dispose of the gathered water from air moisture.

In essence, there are 3 ways:

  1. Self-evaporation (best kind). The water is evaporated and flushed out via exhaust vent with the hot air. Most modern portable air conditioners use this system.
  2. Gravity-drain with optional built-in pump (still good). The collected water is pumped out via a hose.
  3. ‘The bucket’ (not recommended). Some old-school portable AC units have a bucket. There the water is collected and you have to manually empty the bucket when it’s full. Buying such a portable AC is, for lack of a better word, a bad idea.

Summary: Portable AC Unit Inner Workings Are Complex But Handling Is Easy

Portable AC units are quite similar to refrigerators. They have a refrigerant, compressor and the inner workings of expanding gas and compressing it again and again.

Nonetheless, the same level of technical expertise is needed for operating a portable air conditioner as is for the fridge.

Once you plug it in, it’s extremely easy to operate and keeps your home cool.

51 thoughts on “How Do Portable Air Conditioners Work? Basic Principles + Tips”

    • Hello Sue, a single-hose air conditioner sucks the warm indoor air and transfers that heat outsize via the exhaust vent. The text there is not as exact as it should be, we’ll have it corrected, thank you for pointing it out.

  1. What does the fan mode do on a single-hose A/C. I can hear the compressor kick on and off in that mode. Is it drawing in fresh outside air, recirculating the inside air or could it still operating as a cooling system?

    • Hello Betsy, the function of the fan is to move the air around. Specifically, it draws the hot indoor air into the single-hose AC. The air is cooled down and returned into the room, while the hot air (the consequence of cooling air) is expelled outdoor via the exhaust went.

      • That didn’t quite answer the question (I have the same question :-)).

        When in cooling mode, a single-hose AC uses the hose for exhaust. Understood.

        But when in _fan_mode_, does a single-hose A/C use the hose to pull in fresh air from the outside, or does it only recirculate air that’s already inside?

        • Hello Jan, thank you for a clearer question. When in fan mode, only the fan is moving, without the fresh air being sucked in the room. In fan mode, a portable AC unit is basically a big fan, just that. Hope this makes sense.

    • Hello Erik, pointing it toward you will give an impression of the room being cooler than it actually is. Generally, the hot air is lighter than cold air; hence it is located more towards the ceiling. Having vents pointed upwards might, in theory, push that hotter air down. However, this should not have any significant effect on the overall average room temperature.

    • Hello Kathryn, you basically can’t use a portable air conditioner without a window. Every air conditioner needs to have thermal interaction between indoors and outdoors; in the case of portable AC units, that’s a window or a sliding door.

    • Hi, we are venting through the fireplace up the chimney. The fireplace has glass doors and we covered every crack where hot air could come back in with a blackout curtain and towels. Our 8000 BTU unit works for a small area, the problem we have is an open floor plan with no doors in the living room area and halls. It is tolerably cool only if sitting within about 10 feet of the unit. Today I put up folding room dividers and created as small “room” which is much more comfortable and the room dividers don’t even go up to the ceiling. My future plan is to try floor to ceiling blackout curtains to enclose a small room-sized area. We only need to use the portable a/c about 10 days a year so the setup works for us. Ambient temp in large room approx 90 degrees, cooling to about 80.

  2. How dry or moist is the relative humidity expelled from a window style room air conditioner? Since it condenser a lot of moisture into its collection pan and out the drain hose, it would seem that the air expelled out the back of the unit would be both hot and relatively dry.

    • Hello Gerald, you’re right. If an AC unit has a collection pan, the relative humidity of expelled air will be low. Most portable AC units, however, do not have a collection pan. In this case, the expelled air is both hot and humid (high percentage of relative humidity).

  3. Hi
    we have a Haier portable unit. Single hose. It keeps blowing warm air. We have been troubleshooting all day. No luck. The temperature when displayed disappears after a few minutes. Is the suppose to happen. We don’t know what else to do. Any suggestions?

    • Hello Lisa, portable AC units blow the warm air out. You usually get a hose that you have to install through the window for that hot air to be expelled out of the room. Hope this helps.

  4. Hello,

    I recently took my portable a/c unit (CCH YPN-14H) out from storage, and when i plug it in there is a loud buzzing noise coming from it, which appears to be coming from a clear hose that looks like it drains condensation. When i turn it on, it will run for a bit and then give me a F1 error, which the manual states is due to a “High Gas Pressure” error. Do you have an idea of what is causing this and how to fix it?



    • Hello Thomas, “High Gas Pressure” might be caused by a number of complications. It might be best to call an HVAC expert to look at it.

  5. Hi,
    My AC unit has an exhaust hose plus a rubber drain tube both of which expel through, a window.
    There is also a drain tank which needs emptying when it’s full and that is quite frequently. Why would we have both as I would have thought that the drain tube would expel all water in the system.

    • Hello John, usually portable AC units either have a drain tube or a drain tank. Rarely you see both of them in 1 unit; it’s usually designed so in order to give consumers a choice. For example, if you install the unit in the 1st floor with ability to use the drain tube, you can do that. If you want to move it in the basement, where you can’t really use the drain tube, you can use the drain tank.

      A double drain portable air conditioner would usually have a switch in order to decide between draining option; all water through the tube (Option 1), all water to the tank (Option 2), or mixed drained (Option 3); that’s the basic concept. Hope this helps.

  6. I recently purchased a used small room LG portable A/C from a neighbor in Colorado (relatively low humidity) for use in my Camper Van when I travel to Texas (high heat and humidity). I cut a piece of 1/8in paneling to fit inside my front passenger door window and mounted the exhaust hose to it. I place the unit between the driver and passenger seats I traveled to Texas last week and when I set it up, it was 95 degrees Fahrenheit. It took several hours to get the temp down to comfortable sleeping temp but it did work. I noticed that very hot air was blowing outside at the exhaust and the pipe was very warm and giving off heat inside the cab area. I have 2 questions:

    1) Where was the air coming from that was replacing the hot exhaust air? I insulated the van and replaced the seals around the doors so the only place it can be coming in is thru the firewall and/or outside air vents for the vans heating and cooling system. (I understand that hot air is lighter/less dense than cool air but certainly the amount of air being exhausted was greater than that pressure difference. )

    2) Is it safe to insulate that exhaust tube such that less heat returns inside the van to be sucked back in to be cooled again?


    • Hello Pat, that’s an interesting setup. When the hot air is pushed out, the inside air pressure will start decreasing. The created outdoor-indoor air pressure difference will create air inflow in order to balance the pressure difference. Practically, the air can enter through a number of holes in the camper; firewall could be the key here. For such an isolated system (tightly sealed camper, for example), it would make sense to get a two hose portable AC unit. One hose to exhaust the air outdoors and the second one to suck in back in; you won’t get a pressure difference. Insulating the exhaust tube makes sense; just be careful about overheating the insulation material.

  7. I like that you said that the best kind of portable air conditioning units are the ones that can self-evaporate the water gathered from air moisture because it’s convenient and not messy. My husband and I are planning to buy a portable AC for the shed so we can keep cool while we work on DIY projects. I’ll take note of what you said about self-evaporating portable AC because they seem like the wisest choice among all the types. Thanks!

  8. Hello LearnMetrics,

    Thanks for this very informative forum!

    I, like many others dealing with extreme temperatures this summer and being at home a lot, really need some cool advice ; ).

    We recently bought a Single-Hose unit and I have been experimenting a lot with air flow to achieve a somewhat effective “closed” system. I am having trouble bringing the temperature down to a comfortable level, being that I am on the hottest room in the house (roof), which is also relatively large.

    By reading above, I understand that dehumidifying the room helps efficiency, which I will try tonight.

    I do have a few specific questions. ( I realize some of the answers depend on a lot of factors like room size, geo-location and particular unit used, but in order to be helpful to others, consider an average room and typical single-hose unit correctly installed.)

    -Is using the slower fan setting as opposed to the fastest more or less efficient?

    -Is pointing the cold air flow down better than up? (I understand about hot air being lighter than cold, but in terms of a closed room, does it help either way?)

    -Is a higher temperature (still colder than the room temp. ) better than a lower one in terms of achieving a comfortable room temperature faster? (I understand colder will always be desired, but I am asking if it is better not to go full blast with air flow and temp. to bring down the room temperature? … this may be a dumb question.)

    -What is Mpa? I find that it stands for Megapascal, but what does a value of 3 for example mean? Is it only in relation with the type of refrigerant (in my case R290)?

    Thank you in advance, looking forward to your input.

    Daniel in a room too warm.

    • Hello Daniel, thanks for the insightful commentary; let’s try to quite the most out of your single-hose unit.
      1) Fan setting doesn’t affect energy-efficiency significantly over time. The faster fan usually means that the distribution of cooler air is achieved sooner.
      2) Try to point the air flow up. What matters is the air pressure into which the air flow is pointing; air pressure is a bit lower at the top of the room. That may increase energy-efficiency a bit.
      3) It’s not a dumb question in the least. Most people set fan settings on maximum thinking it will achieve lower temperatures; it doesn’t. Practically, you can blast your room with let’s say 200 CFM air flow with the average temperature of 60F. Is 150 CFM with the average temperature of 55F better? Somebody would really make such an experiment to determine if there is a significant difference. The current understanding is that the overall BTU (cooling effect) of a portable AC unit should be the same in both scenarios.
      4) MPa does stand for megapascal; that is 1000.000 Pascals. Pascal is a measure for pressure; ie. 1 Newton of force per 1 square meter. For perspective, standard air pressure is 0.1013 MPa. MPa of 3 would represent quite a big air pressure; about 30 times what we experience in normal circumstances. It is related to the type of refrigerant, yes; during it cycles, the tube in which it flows is constant and temperature changes. Refrigerant pressure, therefore, increases and decreases massively (constant-volume compression).

      Hope this helps in understanding how portable AC work. This summer, right?

  9. There are 2 circular places on the back of my a/c and I don’t know for sure which is to use to attach the hose. Through one of them I can see almost nothing and through the other I can see what looks like 2 small black hose-things.
    Also the hose + connector piece seems to slip a bit.
    It is from my apartment manager.
    What do you advise?
    Thank you,

    • Hello Cathy, do you perhaps have a double-hose portable air conditioner? That would explain having two circular hose attachments on the back. Every portable AC is different; the best thing to do is to consult the manual that comes with the AC. If you don’t have one, you can just input the model into Google and you’ll get a manual in no time.

  10. I live in a Condominium that doesn’t allow exterior air conditioners so I have an 8000 BTU that is venting up through my chimney. The fireplace has glass doors and we’ve covered anyplace the hot exhaust air could get back in with a thermal blackout window curtain and towels. My biggest problem is the lack of doors in the interior of our open floor plan condo. 8000 BTU barely touches 1200+ sqft. I am spending much of the day sitting in front of the unit which is fine for the very few days per year we need it. Today I set up room dividers which don’t reach the ceiling to create a smallish “room” and that area is now quite comfortable. My next idea is to create a larger enclosed space with floor to ceiling blackout curtains.

    • Hello Nancy, for a 1200+ sq ft condo, you would need at least 24,000 BTU portable air conditioner. Making a closed space with about 400 sq ft would be OK; blackout curtains will also help a bit.

      • Thank you! My old (2014) portable A/C says 8000 BTU so doesn’t reflect new doe standards. Is there a way to calculate approx DOE BTU from before those standards were implemented? Thanks again!

        • Hello Nancy, you’re right, the new DOE 2017 standards are not compatible with the old ASHRAE standards. Looking at a few of 8,000 BTU units (old ASHRAE standard), they are now labeled as having 5,000 to 6,000 BTU according to the new DOE 2017 standard. A rule of thumb here is to take old standard BTU figure and reduce it by about 25% to get the new DOE 2017 standard figure.

  11. Hi,

    I have a Delonghi Pinguino Portable Air Conditioner (Pac C110, 11,000 btu). It is running fine but on the AC/Cold air setting it only blows cool air, more like a fan. The air coming out of the back hose is not hot either as it is supposed to be. I have cleaned the filter and checked for water collecting at the bottom and any dust etc. on the coils. It has been in storage unused for a year or two if that is relevant. Anyway, it is not blowing cold air and I have tried the troubleshooting suggestions from the manual, so I am not sure what the problem might be. Any suggestions??

    Thank you so much!!

    • Hello Rachel, seems like compressor issue. Cleaning filters won’t help with that. If compressor is not functioning properly, you’ll see that everything is running normally, but that’s only the exchange of air, not the exchange of heat. You should probably have the unit checked by an HVAC expert or buy a new unit.

  12. I just wanted to say Thank You for the explanation on portable a/c units. I have been exploring the option on purchasing one and had yet to find an article that could simply explain their function. This article really helped A LOT. Thanks again.

  13. Hi, Thank you for all of this information. We actually have 3 different PAC units around our house as it’s an old farm house and didn’t have any A/C. 2 of the units have a 2 drains (the one in the middle that can be run out to drain automatically when in Dry/Dehumidier mode and all 3 have the drain at the bottom that is supposed to be drained periodically into a pan or something. We put them on a small stands and put a container underneath that can catch the water and it has a drain in it that goes out the window along with the above drain (for the 2 with 2 drains). This came about because we had one in the past that leaked everywhere and destroyed my carpet and other items that were on the carpet. We are getting ready to do this with the single drain unit which is a DeLonghi PAC EL290HLWKC-3AL. I’m wondering if there is any reason we shouldn’t do this with the lower drain. Could it cause any issues with the units to have this drain plug open all the time?

    • Hello Cheryl, everything is OK with your comment. Having drain plug open all in the time actually ideal, if you can drain all that water somewhere. It’s called continuous drainage; it’s the most convenient way to drain a portable air conditioner (you don’t need to manually remove water).

  14. We’ve started to get heat waves in our area, San Francisco Bay Area. So we considering getting a portable AC unit for our small house ie: 1000 soft, that we might only use about 3-4 times per year. Would there be any special maintenance for such infrequent use?

    Unfortunately, these heats waves often coincide with fire season, so the outside is quality can be very poor to breathe. Single hose or dual hose system, both will draw outside or into our home. With the single hose, it would be drawing air from every little nook and cranny. With a dual hose, could we put a filter on the intake hose, or would it bog the system down too much?

    • Hello Joe, I can see you have a very specific situation there. Given the poor outdoor air quality, it makes sense to use a single-hose portable AC. It usually has lower EER but that doesn’t matter much if you’re going to use it 3-4 times per year, and it won’t bring the smoky air in your house. Adding a filter sounds good in theory; we have never actually done it in practice. You would do best to contact local San Francisco HVAC experts (here’s a useful form for finding them). Given they are based in California and many people have exactly the same problem with heatwaves and fire season coinciding, they’ll know how to best help you out.

  15. I live in western Oregon where wildfires are currently raging. Air quality in my city is rated hazardous at the moment. I would like to use my single-hose portable air conditioner to reduce the heat in my apartment but note the EPA recommends against this in smoky conditions. Information on your website is very smart and helpful. Could you advise whether or not to follow the EPA recommendation? The quote and weblink are below. Thank you. “If you have a portable air conditioner with a single hose, typically vented out of a window, do not use it in smoky conditions. Consider other cooling options like a fan or window air conditioner. If you have a portable air conditioner with two hoses, make sure that the seal between the window vent kit and the window is as tight as possible.”

    • Hello Benton, EPA recommendations are usually very throughout and trustworthy. We recommend you follow their guidelines in this case as well.

      • My question is similar to Benton’s. I have a dual-hose portable A/C, a Whynter ARC-122DS. I want to know if the Fan Only mode runs the inside air through the air filter, as it does in Cooling mode. Can’t seem to find that info anywhere.

        • Theoretically, fan only mode should only circulate the indoor air. There shouldn’t be an exchange between the indoor and outdoor air. When the cooling is turned on, the indoor-outdoor air exchange kicks in.

    • This is exactly the question I had… Oregon air quality is horrific…. it seems better when the a/c is on vs. off even though it’s recommended NOT to use it… I’m at a loss. Be safe fellow Oregonian.

  16. In Texas tent camping can be miserable during the summer. I have a portable AC already with only the one tube. If I were to fit a duct to the front of the AC (cool air out) and pipe that into the tent with the AC unit running completely outside (intake and out) would this cool the tent more efficiently? With it inside you can see the sides of the canvas tent pull in due to the pressure difference.

    • Hello William, that’s a very insightful case. People hardly believe the pressure really falls with single-hose AC units; tent canvas being pulled toward the center illustrates that very well. With a minimum difference in pressure, the energy-efficiency is certainly higher. It would be best to try it out; you can measure the pressure just be observing the canvas tent pull. If you do, please let us know if it works; it’s actually a great idea in theory.

  17. Hi I Currently have the whynter arc 14s Unit you referenced above with two hoses. We are also currently in oregon with the horrible air quality from the west coast fires. My question is when the unit pulls outside air is it introducing the outside air into the room or is it just using it to extract the cool air and exhaust it back to the outside. We are trying to cool our house but when the outside temperature drops below the inside temperature we are having trouble cooling the room. Obviously we can’t open the windows to cool the house off due to the bad air quality. What should we be doing to properly use the unit given our situation. My concern is I don’t want to be introducing the toxic outside air into our home but still want to cool our house. Thanks for any assistance you can offer.

    • Hello Robert, 2-hose portable AC units do draw outdoor air in order to equalize the pressure (this increases EER rating; the energy efficiency). The currently horrible Oregan outdoor air quality is a problem; it would be best if you turn the AC off.


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