Portable air conditioners: how to choose one that actually cools

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When a portable makes sense

A portable air conditioner puts everything in one box on wheels. Hot air is pushed out through a hose that you run through a window or an opening. It needs no installer and no outdoor unit, so it's the usual choice when:

• you rent and don't want any building work;
• your building doesn't allow anything on the facade;
• you only need to cool one room, such as the bedroom, a few weeks a year.

In return, it uses more electricity than a split for the same cooling and it's noisier, because the compressor is inside the room. If those drawbacks worry you, also look at the portable split.

Single hose or dual hose

This is the most important decision, and the one shops explain least.

• Single hose: it takes air from the room to cool the unit and blows it outside. That creates slight negative pressure, which pulls warm air in through gaps and doors, so some of the cooling is lost. It's the most common and cheapest type.
• Dual hose: one hose draws outdoor air to cool the unit and the other sends it back outside. It doesn't "steal" the air you've already cooled, so it cools faster and better for the same rating.

Real cooling power

Portables are usually rated in BTU/h. To compare that with what your room needs, remember that 1 kW is about 3,400 BTU/h:

In practice, a portable performs below a split of the same nominal rating, especially if it's single hose. Work out your room with the calculator and, if you're borderline, go up a size.

Noise

Because the compressor is in the room, noise is the main complaint about portables, especially for sleeping. Look for the sound level in dB(A) on the spec sheet and compare models on that figure, not on words like "quiet".

Bear in mind that the decibel scale isn't linear: a 3 dB(A) difference means roughly double the sound energy. That's why a few decibels make a big difference at night. If silence is your priority, a split or a portable split will suit you better.

How to vent the hose through a window

1. Use a window seal kit

   A fabric or panel that closes the gap in the window around the hose. Without it, hot air comes straight back in through the same gap.

2. Keep the hose short and straight

   The longer and more bent it is, the worse hot air escapes and the more the hose itself heats the room.

3. Close doors and blinds

   Cool only the room you use and lower the blinds when the sun is on the window.

4. Empty the tank or fit the drain

   Many models evaporate the condensation, but on humid days they may need emptying or a drain hose.

Common mistakes

• Buying a small single-hose unit on price for a large living room. It won't cope on the hottest days.
• Leaving the window gap open. It's the most common reason it "doesn't cool".
• Confusing it with an evaporative cooler. An evaporative cooler isn't an air conditioner: it adds moisture to the air and only cools a little in dry climates. We explain it in cooling without building work.

Frequently asked questions

Is a single hose or dual hose portable better?

Dual hose cools better, because it uses outdoor air to cool the unit instead of blowing out the air you've already cooled. Single hose is cheaper and fine for small rooms and occasional use.

How many BTU do I need for 20 m²?

As a guide, about 2,000 frigories/h, or about 8,000 BTU/h. A 9,000 BTU/h portable is usually enough, although it's worth going up to 12,000 if the room gets a lot of sun.

Do I need permission for a portable air conditioner?

Usually not: there's no outdoor unit and no building work. You just need to vent the hose through a window or opening without damaging the property, which matters if you rent.

Can a portable also heat?

Some models include a heat pump and also work as heating. Check that the spec sheet says so explicitly.