How many BTU do I need for my room?

As a rule of thumb, budget around 340 BTU per square metre of floor area at standard 2.4m ceiling height. A typical UK double bedroom (14-20m²) needs roughly 9,000 BTU. A small box room can manage on 5,000-7,000 BTU. Open-plan living spaces, or any room with south/west-facing glazing, top-floor position, or lots of electronics, should add 10-20% on top of the basic calculation — go up to 12,000-16,000 BTU for those spaces.

Do I need planning permission for a portable air conditioner?

No. A portable unit is a self-contained appliance with a flexible exhaust hose vented through a window using a simple adaptor kit — there's no fixed outdoor condenser and no permanent pipework, so it doesn't trigger planning permission. This is a genuine practical advantage over a fixed split-system unit, which can require planning permission on listed buildings or in conservation areas, and often needs landlord/leaseholder consent in flats.

How loud are portable air conditioners?

It varies a lot by model. For a bedroom, look for a quoted noise figure around 45dB on quiet/night mode. For a living room where background noise (TV, conversation) is already present, 55-65dB is generally acceptable. Always check the quiet-mode figure specifically, not just the peak cooling-mode figure, if noise matters to you.

Do I need an installer for a portable unit?

No — that's the main appeal. You plug it into a standard socket and vent the exhaust hose out of a window using the included kit. Full split-system air conditioning (a separate indoor unit connected to an outdoor condenser) does need a qualified, F-Gas registered installer, since it involves handling refrigerant — that's a materially different, more expensive undertaking than a portable unit.

Will a portable air conditioner make the room damp?

An undersized unit run at full power constantly can struggle with both heat and humidity. An oversized unit can cool the air so quickly that it shuts off before it's run long enough to properly dehumidify the room, which can leave the air feeling clammy even though the temperature has dropped. Getting the BTU sizing right — not just going for the biggest number — matters for comfort, not just for running cost.

Portable Air Conditioner Buying Guide UK (2026) — BTU Sizing

Getting the Size Right Matters More Than the Brand

The single biggest factor in whether a portable air conditioner actually works well in your room isn’t the brand or the price — it’s whether the BTU (British Thermal Unit) rating is correctly matched to the room. Undersize it and the unit runs flat out constantly and still can’t keep up on a genuinely hot day. Oversize it and, counterintuitively, the room can feel damp and clammy, because the unit cools the air so fast it switches off before it’s run long enough to properly remove humidity — plus you’ve paid more for a bulkier unit than you needed.

BTU Sizing Guide

As a starting point, budget around 340 BTU per square metre of floor area, assuming a standard 2.4m ceiling:

Room type	Typical size	BTU needed
Box room / small office	Up to 10m²	5,000–7,000 BTU
Standard double bedroom	14–20m²	8,000–9,000 BTU
Larger bedroom / home office	20–25m²	10,000–12,000 BTU
Open-plan living space	25m²+	12,000–16,000 BTU

Add roughly 10–20% on top of the base figure if any of these apply:

South or west-facing room with large windows getting direct afternoon sun
Top-floor or loft room that heats up under the roof
Room with a lot of electronics or appliances generating their own heat (home office with multiple monitors, a kitchen)

Setting One Up Properly

Position it near a window — the flexible exhaust hose needs to reach outside, and a shorter, straighter hose run is more efficient than a long, kinked one.
Use the window kit properly and seal any gaps. The unit can only cool effectively if the hot exhaust air actually leaves the room rather than partially recirculating around a badly sealed window adaptor — this is the single most common reason people find a portable unit “doesn’t work as well as expected.”
Keep the door closed to the room you’re cooling, and close curtains/blinds on sun-facing windows during the hottest part of the day.
Empty or drain the condensate if your model doesn’t self-evaporate it (check the manual — many modern units handle this automatically in cooling mode, but dehumidifying-heavy use can still produce a collection tray that needs emptying).

Things to Check Before You Buy

Check the quiet-mode noise figure, not just the headline spec, especially for a bedroom — look for something close to 45dB on its quietest setting.
Check the room coverage figure the manufacturer actually quotes, and cross-reference it against your own room’s square metres rather than trusting a vague “great for medium rooms” description.
Look for an Energy Class A rating — running costs add up over a summer, and efficiency varies more between models than people expect.
Check what refrigerant it uses. Newer units using R290 are more environmentally friendly and increasingly what reputable manufacturers are moving to.
Confirm a window kit is actually included, and that it’s a genuine sealed adaptor kit rather than just a vague “hose included” — a poorly-fitting DIY seal noticeably hurts performance.
Know when you actually need something bigger than portable. If you’re trying to cool a whole flat or an entire floor continuously through a UK summer, a portable unit is the wrong tool — that’s when a proper split system, installed by an F-Gas registered engineer, is worth the extra cost and planning-permission check.

Recommended Kits

For a standard UK bedroom or home office (10,000 BTU class):

Meaco MeacoCool Pro Series 10,000 BTU Portable Air Conditioner — Wi-Fi app control, low-noise operation, free flexible window kit included, 2-year parts and labour warranty

For larger or open-plan rooms (16,000 BTU class):

Meaco MeacoCool Pro Series 16,000 BTU Portable Air Conditioner — Class A energy rating, R290 refrigerant, 51-55dB quiet operation, castors for moving between rooms

Meaco is a well-established UK-focused brand in this category, which is why both recommendations above are theirs — consistent build quality and genuine UK customer support both matter more for an appliance you’ll run through an entire summer than shaving a few pounds off the price on an unfamiliar brand.

One Accessory Worth Adding

The single biggest performance killer for a portable unit is a badly sealed window adaptor letting hot air back in — most included kits are adequate but basic. If yours doesn’t seal well against your specific window type (sash windows and uneven frames are the usual culprits):

electriQ Universal Window Seal for All Portable Air Conditioners — a flexible airlock seal that fits around an open window and zips onto your existing exhaust hose, worth the small extra cost if your window shape doesn’t suit the manufacturer’s own kit

The Bottom Line

Get the BTU sizing right for your actual room before anything else — it matters more than brand, price, or extra features. A correctly-sized portable unit needs no installer, no planning permission, and no pipework; it just needs a window to vent through and a properly sealed adaptor kit. If you’re trying to cool more than a room or two continuously through summer, that’s the point to start looking at a professionally installed split system instead.