Guide written by:
Jeremy, Construction site supervisor, Cardiff
There are a few different types of portable air conditioner to choose from, each of which differs in terms of performance:
Monobloc single-hose air conditioners are cost-effective and can be used to cool smaller spaces;
Monobloc dual-hose air conditioners are more expensive, but offer superior performance and use less energy;
Portable split air conditioners tend to be the most expensive option; however, they are also the lightest and quietest units since the condensing unit can be installed outdoors;
Self-evaporating portable air conditioners are affordable and lightweight, but will only be able to cool the air by a couple of degrees (in small rooms measuring less than 15 m²).
Main factors to consider when choosing a portable AC unit:
The surface area (m²) or volume (m3) of the room you need to cool;
The energy class of the appliance rated from A to G or from A++ to D (A and A++ being the most energy-efficient);
The Coefficient of Performance (COP): the higher the COP, the more efficient the air conditioner;
The noise level in decibels: 55 dB on average and even less for the quietest models.
Extra features to enhance user comfort:
A remote control;
A programmer to set start times and air conditioning cycles;
Ventilation mode to allow the unit to act as a fan;
Ionisation to rebalance ions in the air to boost well-being;
Reverse cycle mode to use the air conditioner as a space heater.
In terms of evaluating the performance of an air conditioner, there are two points to note:
The higher the air flow rate (m3 / h), the more efficient the air conditioner.
The cooling capacity (BTU) of air conditioners is converted into kilowatts (kW); 1 kW = 3414 BTU.
Please note: all air conditioners require some form of maintenance.
Contrary to popular belief, air conditioners do not actually produce cold air, but rather work to extract hot air in order to move it from one space to another.
Without going into the technical details, a portable air conditioning unit basically works in a similar way to a fridge. These units use refrigerant fluid to process warm air which is then 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 now operate automatically. A temperature sensor is used to measure the ambient temperature of a room 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 to the space to reach your target temperature. The efficiency of this process depends on the power of the unit and its compression capacity.
There are three main types of portable air conditioner: monobloc systems, split systems and self-evaporating portable air conditioners.
Monobloc 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 inside a single unit mounted on wheels. While ideal to use as an additional air conditioning system and easy to move from one room to another, monobloc 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 monobloc models also provide a ventilation-only or dehumidifier mode and are therefore able to work as a fan or to decrease humidity without actually cooling the air. High-quality air conditioning units are usually also programmable by means of a built-in timer which can be used to set start and stop times.
Monobloc 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 compression which requires more energy.
Portable split air conditioners work exactly like monobloc models, but consist of two separate units. 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 monobloc units, power ratings vary from 2000 to 3500W. Most split air conditioners also offer ventilation-only and dehumidifying modes. Like some portable monobloc systems, high-quality split models can also be programmed. They are, however, more expensive than their monobloc counterparts.
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 — even if they have a fairly limited capacity. The downside is that they are noisy and are usually ineffective in rooms measuring over 15 m2. While these units provide a useful occasional solution, they lack both the efficiency and level of control of other models (i.e. monobloc or split). As such, they do not offer the cool and comfort you'd expect from a real AC unit.
In addition to choosing between a monoblock or split model, consider the following features to ensure that the air conditioner you select is able to meet your needs.
Cooling capacity is expressed in BTU (British Thermal Units). Just remember: 1 BTU = 1055 Joules (J) and 1W equates to 3.414 BTU. Cooling capacity 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 in BTUs
Wattage of air conditioning unit
Maximum room volume
37 m 3
62 m 3
87 m 3
135 m 3
Mobile air conditioning units are relatively energy-intensive. Energy consumption is therefore an important 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 indicates the efficiency of appliances as a ratio between electrical power consumed and refrigeration power restored. To put it simply, the higher the COP, the more efficient the air conditioning unit!
As mentioned above, portable air conditioners (especially monobloc models) are often quite noisy. In fact, there is no such thing as a totally silent model! While 50dB (decibels) represents an acceptable level of noise, units that lack adequate soundproofing can reach 70 or 75dB. Noise level often has a significant impact on price, but it might be a fair price to pay to keep cool in (relative) silence.
There are a few air conditioner accessories to choose from which should help to maximise 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 features like temperature management, delayed start, set cycles, and so on.
Some air conditioners also offer alternative modes, such as ventilation-only mode (the unit then acts simply as a fan) or dehumidifier mode.
This mode allows you to rebalance the ions in your home which is said to enhance general well-being.
Remote controls can be very handy, depending on the intended use and location of your air conditioning unit.
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.
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.
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.
As with any other appliance, maintenance is needed 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.
You should also remember to descale your air conditioning unit once a year.
These days, decent air conditioning can be bought on all kinds of budgets. However, you do need to know how to use your air conditioning unit effectively.
The first thing to remember is that you need to place your air conditioner near a window (or other evacuation route) regardless of the type of model (monobloc or split). Remember that the shorter the evacuation circuit, the better the performance.
Avoid using a flexible hose that is excessively long as this will cause condensation to 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 things start to get warmer again.
Guide written by:
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 restoring and building an extension to a bungalow in the heart of the Welsh countryside. My experience in manual work and my knowledge means I am proud to be of service. Terraces, interior design, roofing, plumbing, electrics, anything goes! My wife, daughter and I, built almost everything we have from scratch! So to answer all of your questions and advise you on choosing your tools? Easy!