Are portable air conditioners worth it?

Portable air conditioning is judged too harshly by people who have never needed it and too kindly by the marketing. The physics behind the disappointment is specific and worth understanding before spending.

Safety

Step by step

1. Understand the single-hose problem.Most units have one hose. They blow hot air out of it, which lowers the pressure in the room, which pulls warm air in through every gap to replace it. That is why the room never gets as cool as the specification implies.
2. Consider a dual-hose model.Two hoses — one drawing outside air in to cool the condenser, one exhausting it. It does not depressurise the room and it is meaningfully more effective. More expensive, bulkier, and worth it if you will use it every summer.
3. Seal the window properly.The hose has to leave through a window, and the gap around it lets hot air back in. A proper window seal kit rather than a towel makes a large difference and costs very little.
4. Match the unit to the room size.Rated in BTU or kilowatts against a room area. Undersized, it runs constantly and never reaches temperature; substantially oversized, it short-cycles and does not dehumidify. Measure the room first.
5. Check the noise rating.Stated in decibels. These are not quiet appliances and the compressor cycles on and off. In a bedroom that matters more than a couple of degrees, and it is the most common regret.
6. Check the running cost.They draw a lot of power — often 1kW or more. Multiply the rating by your electricity price and the hours you would run it. For a few nights a year that is fine; for daily use it is substantial.
7. Understand the condensate arrangement.They extract water from the air, which has to go somewhere — a tank you empty, or a continuous drain hose. A unit that stops when the tank fills at three in the morning is not solving your problem.
8. Do the free things first.Shading the windows during the day, opening up at night, exhaust fans, loft insulation. These cost nothing or very little and they reduce how much cooling is needed at all.
9. Compare with the alternatives honestly.A good fan arrangement costs a fraction and handles most British summers. A fixed split-system air conditioner is far more efficient and quieter but needs installation and planning consideration. Portable sits awkwardly between the two.
10. Buy it for one room, not the house.They cool the room they are in and nothing else. A bedroom you cannot sleep in is the case that justifies one; a whole house is not.
11. Check where it will live in winter.They are large and heavy. If there is nowhere to store it for nine months, that is a real consideration and it is the thing people forget in July.
12. Consider an evaporative cooler only in dry conditions.They are cheaper and add humidity rather than removing it. In a humid British summer that generally makes a room feel worse, so they are rarely the right answer here.

Tips

• If you buy one, buy the window seal kit at the same time. Without it a large share of the cooling is lost around the hose.
• Run it for half an hour before bed with the door shut rather than all evening. Cooling one room and then keeping it closed is far more effective.
• Check the noise figure against a fan you already own. The gap is usually larger than people expect.

Common mistakes

• Running the exhaust hose into the room — It is expelling the heat it removed plus the heat the compressor generates, so the room gets hotter. The hose must go outside.
• Buying one to cool a whole house — They cool the room they occupy and nothing beyond it. For a house, the answer is shading, ventilation and insulation rather than a portable unit.

If it doesn't work

Questions people ask