Portable air conditioner buying guide

Portable air conditioner buying guide

Jeremy, construction site supervisor, Cardiff

Guide written by:

Jeremy, construction site supervisor, Cardiff

134 guides

Essential for keeping cool in the summer months, portable air conditioners allow you to freshen up the air and lower the overall temperature of your living space. Whether you choose a monoblock or split unit, your decision will come down to the volume of the room and the features on offer. Read on for our top tips!

Important features

  • Monoblock air conditioners
  • Split air conditioners
  • Air coolers
  • Volume and surface area
  • BTU and power
  • Coefficient of performance
  • Filtering and noise level
  • Programming
  • Reverse cycle
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Portable air conditioners: the essentials


There are a few different types of portable air conditioners which differ in terms of performance:

Main factors to consider when choosing a portable AC unit:

Please note: all air conditioners require some form of maintenance.

How do air conditioners work?


Contrary to popular belief, air conditioning doesn't actually produce cold air, but rather works to extract hot air from one space to another.

Without going into any technical details, portable air conditioning units work in a similar way to fridges. They use refrigerant fluid to process warm air which is either released outdoors or condensed depending on the type of unit you have.

Air conditioners offer an almost instantaneous cooling effect when the unit is switched on and the vast majority of mobile air conditioning units these days operate automatically. A temperature sensor is used to measure the ambient temperature in real time allowing the unit to calculate the level of excess heat to be extracted and the amount of fresh air to be returned in order to reach your target temperature. This process depends on the power of the unit and its compression capacity.

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Different types of portable air conditioners

There are three main types of portable air conditioner: the monoblock systems, split systems and the self-evaporating portable air conditioners.

Monoblock portable air conditioners

Single-hose monoblock air conditioners


Monoblock single-hose air conditioners are the simplest and quickest type of unit to use. As the name suggests, the whole air con mechanism is incorporated in a single unit mounted on wheels. Ideal as an additional air conditioning system and easy to move from one room to another, monoblock units do require exterior venting. This venting is performed by a flexible hose (100–150 mm in diameter) that can be fed through a window or a vent in an external wall. Power ratings vary from 2000–3500 W, meaning a surface area of over 35 m2 can be serviced by a single unit. However, pay attention to the level of soundproofing on the casing as this type of air conditioning unit is often noisy (>60 dB). More sophisticated monoblock models also provide a ventilation only or dehumidifier mode to move ambient air or decrease humidity without actually cooling the air. High-end air conditioning units are also programmable by means of a built-in timer which can be used to set start and stop times and so on.

Dual-hose monoblock air conditioners


Monoblock dual-hose air conditioners feature two hoses: one for collecting outdoor air and the other for releasing warm air. This process allows you to cool down ambient air without bringing in any hot air from outdoors. What's more, this process doesn't involve pressure which requires more energy.

Split air conditioners


Portable split air conditioners work exactly like monoblock models, but consist of two separate parts. The condensing and compression unit is installed outside the property while the portable ventilation unit can be placed indoors (as long as it is connected to the external unit via a flexible hose). As you may have guessed, split models are less portable than monoblock units since the ventilation unit has to be positioned close to the external compression unit. The major advantage of split models is that the mobile ventilation unit is lighter and less bulky and produces much less noise! Like monoblock units, power ratings vary from 2000 to 3500W. Most split air conditioners also offer ventilation-only and dehumidifying modes. Like some portable monoblock systems, high-end split models can also be programmed. They are, however, more expensive than their monoblock counterparts.

Self-evaporating portable air conditioners


Self-evaporating air conditioners are designed to release excess moisture along with the warm air they extract meaning you won't have to empty a drip tray.

These devices are affordable, small, lightweight and able to cool down small spaces – if only slightly! The downside is that they are noisy and are usually ineffective in rooms measuring over 15m2. While these units provide a useful occasional solution, they lack both the efficiency and control of other models (i.e. monoblock or split). As such, they do not offer the cool and comfort you'd expect from a real AC unit.

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Portable air conditioner features

In addition to choosing between a monoblock or split model, consider the following features to ensure that the air conditioner you select meets your needs.

Cooling capacity


Cooling capacity is expressed in BTU (British Thermal Units). 1 BTU = 1055 Joules (J) and 1W equates to 3.414 BTU. This is the main factor in determining whether or not a given model is suitable for your space. As a rough guideline, an air conditioning unit must have a minimum output of 7000 BTU (~1950W) for a space up to 15m², 9000 BTU (2500W) up to 25m² and 12000 BTU (3500W) up to 35m². Account for about 100–130W per m² (assuming a ceiling height of around 2.5 m) and size up if the space you want to cool has bay windows, french doors or if it is south-facing.


Cooling capacity and room size comparison

Cooling capacity in BTUs

Wattage of air conditioning unit

Room size

Maximum room volume

7000 BTU

2000 W

15 m²

37 m 3

9000 BTU

2500 W

25 m²

62 m 3

12000 BTU

3500 W

35 m²

87 m 3

14000 BTU

4100 W

54 m²

135 m 3

Energy consumption


Mobile air conditioning units are relatively energy-intensive. Energy consumption is therefore a factor to consider when making your choice. Like other appliances, air conditioning units are classified according to their energy consumption (from A to G or A+++ to D). Ideally, you'll want to look for a class A to A+++ rating.

Coefficient of performance

Coefficient of performance indicates the efficiency of devices as a ratio between electrical power consumed and refrigeration power restored. To cut to the chase, the higher the COP, the more efficient the air conditioning unit!

Noise level

As mentioned above, portable air conditioners (especially monoblock models) are often quite noisy. There is no such thing as a totally silent model! While 50dB (decibels) represents a low level of noise, the most poorly soundproofed units can reach 70 or 75dB. This often has a significant impact on price but it might be a fair price to pay to keep cool in relative silence.

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Additional features for portable air conditioners

There are a few air conditioner accessories designed for greater comfort and ease of use.



It's well worthwhile to be able to program your air conditioner if you want to be able to arrive home to an already perfectly cool living space, or if you want to power down automatically when everyone's in bed. Programming can help with the electricity bill too (through temperature management, delayed start, set cycles etc.).

Ventilation-only and dehumidifier modes 

Some air conditioners also offer alternative modes, such as ventilation-only mode (the unit then acts simply as a fan) or dehumidifier mode.

Ionisation mode

This mode allows you to rebalance the ions in your home – a process linked to general well-being.

Remote control


Remote controls can be very handy, depending on the intended use and location of your air conditioning unit.

Activated carbon filter and electrostatic filter

Some air conditioning units are equipped with additional filters to purify the cooled air they expel. Activated carbon filters are effective at removing odours while electrostatic filters are great for fighting bacteria and dust. These features are especially useful if you or a member of your family suffers from respiratory problems such as asthma.

Noise level

To avoid the nuisance of a loud air conditioner, choose a unit with the Eurovent label, or with a Sleep or equivalent setting. This will ensure you are exposed to only low decibel (dB) levels.

Reverse cycle air conditioners

Some air conditioners offer reverse cycles meaning they also function as heaters. Before you jump at this exciting prospect, always be sure to check the coefficient of performance of air conditioning units before you buy.

Caring for your portable air conditioner


As with any other appliance, maintenance is necessary to ensure your air conditioning unit keeps functioning as expected.

If you opt for a split system, you'll have to work your magic on both parts of the system: outside and inside. For monoblock systems, everything happens inside the one box. Maintenance is generally limited to cleaning the filters and draining the water tank. Overall, you shouldn't have too much trouble, whichever model you go for.

However, you should also remember to descale your air conditioning unit once a year.

Final tips on choosing your portable air conditioner


These days, decent air conditioning is within everyone's reach! However, you do need to know how to use your air conditioning unit.

The first thing to remember is that you need to place your air conditioner near a window (or other evacuation route) regardless of type (monoblock or split): the shorter the evacuation circuit, the better the performance.

Avoid extending the flexible hose that comes with your unit at all costs. If it is too long, condensation will accumulate inside and mould will quickly set in.

When setting your air conditioning unit, the target temperature should be no more than 8°C lower than the maximum outdoor temperature to avoid thermal shock (5°C is ideal).

To maintain good air quality, clean the filters regularly. Drain the water tank(s) at the same time.

In terms of energy consumption, for an average air conditioning unit, expect an increase of about 15% per month for a daily use of 3–4 hours. For this reason, it's best to choose a programmable model with a class A energy rating and a high COP.

In the autumn, before unplugging your air conditioner, run it for a few hours in ventilation-only mode (if possible) to dry all the pipes and ducts for storage. Follow the same routine in spring for several hours when the heat starts to pick up.

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Guide written by:

Jeremy, construction site supervisor, Cardiff, 134 guides

Jeremy, construction site supervisor, Cardiff

Electrician by trade, I first worked in industrial estates where I installed, wired and fixed a large number of electrical installations. After this, I managed a team of electricians for this type of work. 10 years or so ago, I turned to building and construction. From the modest family home, to gyms and theatres; I have been able to coordinate, audit and organise all sorts of construction sites. for 4 years now, I am restaoring and bulding an extrension to a bungalow in the heart of the welsh countyside. My experience in manual work and my knowledge means I am proud to be of service. Terraces, interior design, roofing, plumbing, electricty, anything goes! We have, my wife, daughter and I, built almost everything we have from scratch! So to answer all of your questions, and to orientate and advise you on coosing your tools? Easy!

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