Portable Air Conditioner Buying Checklist: 10 Things to Check Before You Buy

Quick answer
Ten minutes of checking prevents the two purchases people regret: a unit that can’t be vented through their windows, and one that’s the wrong size for the room. Those are the top two by a distance. Work down this list in order — venting first, because a unit you can’t vent is unusable rather than merely disappointing, and it’s the one thing nobody thinks about until the box is open.

Print this, or work through it with the listing open.

1. Where will the hose go?

Check this first. A portable air conditioner must vent hot air outside — through a window, a wall vent, or a door. Without that it does nothing useful at all.

Go and look at the window you intend to use. Does it open? How far? Is it a casement that opens outward, a sash, a tilt-and-turn, a narrow top light, a roof window?

The supplied slider kit is designed for sash and sliding windows, which are uncommon in UK homes. On a casement it often won’t fit at all. Our seal kits guide covers the alternatives, and there’s a solution for almost every window — but work it out before ordering, not after.

If you rent or hold a lease, anything drilled needs written permission.

2. What size do you actually need?

Start at roughly 500–600 BTU per square metre, then adjust for glazing, aspect, ceiling height, a roof above, and equipment in the room.

Both errors cost you. Undersized means running continuously without reaching temperature. Oversized means short cycling — cooling the air fast, shutting off before removing much moisture, and leaving a room that’s cold and clammy.

Our sizing guide works through it properly, with the adjustments that matter more than the starting figure.

3. How loud is it — at which fan speed?

The number one cause of a unit that gets bought and then not used.

A decibel figure quoted without the fan speed tells you very little. Units are considerably louder at full speed than at their advertised minimum. Where a manufacturer publishes a specific quiet-mode figure, that’s the number that matters for a bedroom.

Be aware published and independently measured figures can differ — Trusted Reviews measured 58.5 dB fan-only on the Meaco Pro 9000 against a published 52 dB low-fan figure. Not a scandal, but treat the published number as a floor rather than a ceiling.

Compressor cycling is the intrusive part, more than steady fan noise. Our quiet units guide covers choosing for a bedroom.

4. What’s the energy rating?

Determines running cost for the same cooling. An A-rated unit costs more up front and less per hour — over a heavy summer that gap narrows, which is why the cheapest to buy and the cheapest to own aren’t always the same unit.

Our running cost guide covers the calculation, and our units explainer covers why BTU and watts are different numbers that people constantly confuse.

5. Does it have continuous drainage?

Underrated, and it decides whether you can run it unattended.

Every unit produces condensate. Without a continuous drain option, the tank fills and the unit shuts off — typically overnight, with nobody there. Almost all units have a drain port; check the listing confirms it, and check whether a hose is included.

Our tank full guide covers setting it up.

6. Single hose or dual hose?

A single-hose unit draws its condenser air from the room, putting the room under slight negative pressure — so it pulls warm outside air in through every gap. A dual-hose unit draws that air from outside instead, which is more efficient.

Dual-hose units are less common and harder to vent. Our comparison covers the trade-off — and note that sealing properly matters more than which type you buy.

7. How heavy is it, and can you move it?

These commonly weigh 25–35kg, and many have no proper handholds. Check the stated weight, and think about:

Getting it up the stairs on delivery day
Moving it to storage each autumn
Whether you’ll be doing that alone

Higher capacity means heavier. Our moving guide covers doing it safely.

8. Where will it live for eight months?

Genuinely worth thinking about before you buy, particularly in a flat or a shared house. These are bulky, they must be stored upright, and they need somewhere dry.

Our storage guide covers the requirements.

9. Does it heat as well?

A reverse-cycle unit works in both directions, so it isn’t sitting unused for most of the year — and a heat pump delivers more heat per unit of electricity than a plug-in resistive heater.

The check that matters: is the heating output stated separately? “4-in-1” frequently means cool, fan, dehumidify and timer rather than heating. And heating output is often lower than cooling output, so if winter use is the point, size on that figure. Our heat pump guide covers it.

10. Warranty, brand and where you’re buying from

Manufacturer warranty length — real value on an appliance with a compressor, and a legitimate reason to choose one model over another.
Can you find the specifications on the manufacturer’s own site? If a model exists only as a marketplace listing with no supporting documentation, that’s a signal.
Buying from a trader means the Consumer Rights Act applies in full — goods must be of satisfactory quality, fit for purpose and as described, with six years to bring a claim in England and Wales, five in Scotland. Our warranties guide covers what that means in practice.
Check the refrigerant and minimum room size. Most modern units use R290, and the stated minimum floor area exists because of the charge limit — relevant for small rooms. Our R290 guide explains it.

Before you order — the free things

Do these first. They may drop you a capacity class, which means a cheaper, quieter, lighter unit — or mean you don’t need one.

☐ Shade the window from mid-morning for a week and see what changes
☐ Purge ventilate at the right time — our timing guide covers it
☐ Close the door to the room
☐ Switch off electronics in there
☐ Put a thermometer in the room so you know what you’re actually dealing with

The checklist

☐ Venting route confirmed, and the kit will fit
☐ Room measured and BTU calculated with adjustments
☐ Noise figure checked, with the fan speed it refers to
☐ Energy rating checked
☐ Continuous drain port confirmed
☐ Single or dual hose decided
☐ Weight checked, and moving it thought through
☐ Winter storage space identified
☐ Heating output checked separately, if you want one
☐ Warranty, brand documentation and retailer checked

Frequently asked questions

What’s the single most common mistake?

Not checking the venting. People buy on BTU and price, then discover the kit won’t fit their window. It’s solvable with a cut panel, but it’s better known beforehand.

Should I buy the biggest I can afford?

No. Oversizing causes short cycling and poor dehumidification, plus more noise, weight and cost. Size to the room.

When’s the best time to buy?

Autumn and winter — demand collapses and clearance happens. Our timing guide covers the calendar.

Is a cheap unbranded unit a false economy?

Not automatically — but check you can find real specifications, an energy rating and a stated room range. A listing with a BTU number and nothing else is a gamble on an appliance you’ll keep for years.