How Do Portable Air Conditioning Units Work?
When temperatures rise during a heatwave in the UK, keeping your home cool quickly becomes a priority, but it can also be very difficult. Many of our homes are well insulated to help keep the heat in during our colder winters, but this also means they retain it when the temperatures rise throughout Summer.
Fans, air coolers and portable air conditioning units can all help make a room feel more comfortable, but they do not all work in the same way.
Portable air conditioning units have become especially popular during hot weather because they actively cool the air, rather than simply moving it around. During the June 2026 heatwave, parts of the UK saw record-breaking temperatures, with prolonged hot days, high humidity and unusually warm nights making it harder for homes to cool down naturally.
If you are thinking of buying a portable air conditioner, or you already have one and want to get the best results from it, it helps to understand how it works, where it should be placed and what can affect its performance.
Below, we explain how portable air conditioning units work, what to consider before buying one and how to use yours effectively during hot weather.
READ OUR LATEST HEATWAVE ADVICE ON AIR CONDITIONING, FANS & AIR COOLERS
Fans vs Air Coolers vs Air Conditioning: Which Is Best During a Heatwave?
Should You Close Windows and Doors When Using a Fan, Air Cooler or Portable Air Conditioner?
What Is a Portable Air Conditioning Unit?
A portable air conditioning unit is a cooling appliance designed to reduce the temperature in a single room. Unlike a fan, which moves air around the room, a portable air conditioner removes heat from the air and sends that heat outside through an exhaust hose.
Most portable air conditioners are freestanding units on wheels, making them easier to move between rooms than fixed air conditioning systems. They usually need to be placed near a window, door or vent so the exhaust hose can release warm air outside.
This makes them a useful option for bedrooms, home offices, living rooms and conservatories, particularly during short periods of very hot weather.
How Do Portable Air Conditioning Units Work?
Portable air conditioners work by drawing warm air from the room into the unit. Inside the appliance, the air passes over cold evaporator coils filled with refrigerant. This refrigerant absorbs heat from the air, which lowers the air temperature before it is blown back into the room.
At the same time, the heat that has been removed from the air needs somewhere to go. The unit transfers this heat to a condenser coil and expels it outside through the exhaust hose.
In simple terms, a portable air conditioner works by:
- Pulling warm air from the room into the unit
- Passing the air over cold coils to remove heat
- Blowing cooler air back into the room
- Sending the extracted heat outside through an exhaust hose
- Removing some moisture from the air as it cools
This process continues until the room reaches the temperature you have selected, or until the unit is switched off.
Why Does a Portable Air Conditioner Need a Hose?
The exhaust hose is one of the most important parts of a portable air conditioning unit. Without it, the heat removed from the room would have nowhere to go.
If the hose is not vented outside, the unit will blow cool air from the front but release warm air back into the same room. This means the room will not cool properly and the appliance will waste energy.
For the best results, the hose should be fitted securely through a window, door or suitable wall vent. Most portable air conditioners come with a window kit, or one can be bought separately. This helps seal the gap around the hose so warm air cannot easily come back into the room.
Should Windows and Doors Be Closed When Using Portable Air Conditioning?
Yes, windows and internal doors should usually be kept closed when using a portable air conditioning unit.
The only opening should be the one needed for the exhaust hose. Any gaps around the hose should be sealed as much as possible. If a window is left wide open, warm air can come straight back inside, which makes the unit work harder and reduces cooling performance.
Internal doors should also be kept closed so the air conditioner can focus on cooling one room. Portable units are not usually designed to cool an entire home, so trying to cool several connected spaces at once can make them less effective.
For the best setup:
- Keep windows closed apart from the exhaust hose outlet
- Use a window sealing kit where possible
- Keep internal doors closed while the unit is running
- Close curtains or blinds to block direct sunlight
- Use the unit in the room you are actually spending time in
What Is the Difference Between a Fan, Air Cooler and Portable Air Conditioner?
The main difference comes down to how each appliance cools the space.
A fan does not lower the room temperature. It moves air around, helping sweat evaporate from your skin and creating a cooling breeze. Fans are simple, affordable and useful for everyday cooling.
An air cooler, also known as an evaporative cooler, uses water evaporation to cool the air before blowing it back into the room. Air coolers can feel more effective than a fan, but they add moisture to the air and work best in warm, dry conditions.
A portable air conditioner actively removes heat from the room. This makes it the most powerful option during very hot weather, but it also uses more energy and needs to be vented outside.
If you want low-cost personal cooling, a fan may be enough. If you want a step up from a fan without using as much energy as air conditioning, an air cooler may be suitable. If you need to reduce the actual temperature in a room during a heatwave, a portable air conditioning unit is usually the most effective choice.
What Should You Consider Before Buying a Portable Air Conditioner?
Before buying a portable air conditioning unit, it is important to think about where and how you will use it. Choosing the right unit can make a big difference to performance, comfort and running costs.
Room Size
Portable air conditioners are designed to cool specific room sizes. Cooling power is usually measured in BTU, which stands for British Thermal Units.
As a general guide, smaller rooms may only need a lower BTU unit, while larger rooms, conservatories or rooms with lots of sunlight may need a more powerful model. If the unit is too small for the room, it may run constantly without cooling the space properly. If it is too powerful, it may use more energy than necessary.
Always check the manufacturer’s room size guidance before buying.
Window Access
A portable air conditioner needs somewhere to vent warm air outside. Before buying, check whether the room has a suitable window, door or vent for the exhaust hose.
You should also check whether the supplied window kit is suitable for your window type. Some kits work better with sliding windows, while others may need extra sealing accessories for casement windows or patio doors.
Running Costs
Portable air conditioners are more powerful than fans and air coolers, but they cost more to run. Energy use varies depending on the model, cooling mode, room temperature and how long the unit is running.
To estimate running costs, check the wattage of the unit and multiply it by the number of hours used and your electricity unit rate. For example, a 1,000W unit uses around 1kWh of electricity per hour when running at full power.
This does not mean the unit will always use the maximum amount of energy, as many models cycle on and off once the target temperature is reached. However, it is still worth using portable air conditioning carefully and only when needed.
Noise Levels
Portable air conditioners contain a compressor and fans, so they are usually louder than a standard fan. This is worth considering if you plan to use one in a bedroom, nursery, home office or living room while watching TV.
Look at the decibel rating before buying and check whether the unit has a sleep mode, timer or quieter fan setting.
Drainage and Moisture
As portable air conditioners cool the air, they can also remove moisture. Some units collect this water in an internal tank, while others evaporate much of it through the exhaust hose.
In humid weather, you may need to empty the tank or connect a drainage hose. Always follow the manufacturer’s instructions so the unit continues to work properly.
How to Make a Portable Air Conditioner Work Effectively
A portable air conditioning unit will work best when the room is prepared properly. Small changes can make a noticeable difference to how quickly the room cools and how much energy the unit uses.
Start Cooling Before the Room Gets Too Hot
It is easier to keep a room comfortable than it is to cool it down once it has become extremely hot. During a heatwave, consider switching the unit on before the room reaches its hottest point.
This can be especially useful in bedrooms during the evening, as walls, floors and furniture can hold heat long after the outdoor temperature has dropped.
Keep Sunlight Out
Direct sunlight can quickly heat a room, especially through large windows, patio doors or conservatory glass. Keep curtains, blinds or shutters closed during the hottest part of the day to reduce heat gain.
This helps the air conditioner work more efficiently because it is not fighting against constant heat from the sun.
Seal the Window Gap
A poorly sealed exhaust hose can reduce performance. If warm air is able to come back into the room around the hose, the air conditioner has to work harder to maintain a comfortable temperature.
Use a window sealing kit where possible and check that the hose is securely fitted. Try to keep the hose as short and straight as you can, as long or kinked hoses can make it harder for warm air to escape.
Close Internal Doors
Portable air conditioners are best used for single-room cooling. Keeping internal doors closed helps trap the cooler air in the room you are using.
If doors are left open, warm air from hallways, landings or other rooms can enter the space. This can make the unit run for longer and reduce how quickly the room cools down.
Keep the Filter Clean
Most portable air conditioning units have a filter that helps catch dust and particles as air passes through the appliance. If the filter becomes clogged, airflow can be reduced and the unit may not cool as effectively.
Check the filter regularly during hot weather and clean it according to the manufacturer’s instructions. This is a simple maintenance step that can help improve performance and extend the life of the unit.
Avoid Adding Extra Heat to the Room
During a heatwave, everyday appliances can add more heat to your home. Ovens, hobs, tumble dryers, gaming PCs and large TVs can all increase the temperature in a room.
Where possible, avoid using heat-producing appliances in the room you are trying to cool. This can help your portable air conditioner work more effectively.
Common Portable Air Conditioner Mistakes to Avoid
If your portable air conditioner is not cooling as well as expected, the problem may be the setup rather than the unit itself.
Common mistakes include:
- Leaving the window open around the exhaust hose
- Using the unit in a room that is too large
- Leaving internal doors open
- Placing the unit too far from the window
- Allowing the exhaust hose to bend or kink
- Forgetting to clean the filter
- Setting the temperature too low and leaving it running constantly
- Blocking the air intake or outlet
A portable air conditioner needs good airflow, proper ventilation and a closed room to work at its best.
Are Portable Air Conditioners Expensive to Run?
Portable air conditioners cost more to run than fans because they actively cool the air using a refrigeration system. Fans are cheaper because they only move air around the room.
However, there are ways to keep running costs under control. Use the unit in one room, close doors and windows, seal the exhaust hose properly and use timers where available. Once the room feels comfortable, you may be able to raise the set temperature slightly or switch to fan mode.
It is also worth thinking about when you use the unit. Running it for a short period to cool a bedroom before sleep may be more efficient than leaving it on all day in a room you are not using.
Can a Portable Air Conditioner Cool More Than One Room?
In most cases, a portable air conditioner is best used to cool one room at a time. While cool air may move slightly into nearby spaces if doors are open, the unit will usually become less effective because it is trying to cool a much larger area.
For the best results, use the unit in the room where you need it most. This might be a bedroom at night, a home office during the day or a living room in the evening.
Is Portable Air Conditioning Worth It During a UK Heatwave?
For many UK homes, portable air conditioning is most useful during periods of very hot weather, especially when indoor temperatures stay high overnight. It can be particularly helpful in bedrooms, loft rooms, flats, conservatories and home offices that become uncomfortable during heatwaves.
However, it is important to use it correctly. A portable air conditioner is not just a plug-in fan. It needs a properly fitted exhaust hose, a suitable room size and a closed-off space to deliver the best results.
If you only need a gentle breeze, a fan may be the better low-cost option. If you want cooler airflow without the higher running costs of air conditioning, an air cooler may be a good middle ground. But if you need to actively lower the temperature in one room during very hot weather, a portable air conditioner is likely to be the most effective appliance.
Quick Checklist for Getting the Best from Your Portable Air Conditioner
Before using your portable air conditioner during a heatwave, make sure you check the following key areas:
Used properly, a portable air conditioning unit can make a real difference during hot weather. By understanding how it works and setting it up correctly, you can cool your room more effectively, avoid wasting energy and stay more comfortable when temperatures rise.
Keep up to date with the latest stock of portable air conditioning units, plus our range of fans and air coolers on the Plumbworld website.
Are you planning a new bathroom or kitchen makeover? Shop online with Plumbworld for the guaranteed lowest prices on a wide range of premium brands, PLUS next day delivery options and our renowned customer service.
Sign-up to our newsletter for the first time and get £10 off your order when you spend over £300. Plus, you’ll discover all of Plumbworld’s latest offers, newest product launches and advice from our experts.
Make sure you follow us on social media. Don’t forget to share your bathroom or kitchen makeovers - tag us in your photos to be featured in our posts.
Find us at:
Facebook | Twitter | Instagram | TikTok | Pinterest
Don’t forget to check out the rest of our blog for the latest bathroom and kitchen buying guides and advice from our experts.