Portable or split air conditioning: which is better in London?

The quick comparison

London searches for portable air conditioners spike every heatwave, and for good reason: you can buy one today and plug it in tonight. But the two types work very differently.

	Portable	Split system
Where the compressor is	in the room	outside
Noise in the room	loud	quiet on low fan
Window	hose through an open window	none, one small hole through the wall
Cooling effectiveness	limited, heat leaks back via the hose	strong and steady
Heating	some models	most models, efficiently
Permission needed	usually none	landlord, freeholder, sometimes planning
Installation	none	F-gas qualified engineer
Moves between rooms	yes	no

Why portables struggle

A portable takes heat out of the room air and dumps it outside through a wide flexible hose. The hose itself gets hot and radiates some of that heat straight back into the room. Most portables are single hose units: they blow room air out through the hose, so the same amount of air has to come back in from somewhere, usually warm air from outside through doors, gaps and the window opening. On a 30°C afternoon, that is a lot of warm air.

Then there is the window. The supplied window kit is designed for sliding or casement windows. In a Victorian or Georgian sash window, which is what much of Islington, Camden and Hackney have, you end up lifting the bottom sash and stuffing the gap. It rarely seals, the room still gains heat and the window cannot be locked.

Why splits work better in London rooms

A split system keeps the noisy compressor outside, so the indoor unit can run slowly and quietly. There is no hot hose in the room and no open window. The only link to the outside is a hole about the size of a drainpipe, through which the refrigerant pipes, cable and drain pass. Most modern splits are reversible, so they also heat the room in spring and autumn, and our split system page explains how they work.

For a top floor flat in a converted Islington terrace, a south facing home office or a loft bedroom, a split is the difference between a room you can use in July and one you avoid.

When a portable is the right choice

There are real situations where a portable makes sense:

• Renting: you cannot fix anything to the building without your landlord’s consent, and the landlord may need the freeholder’s too
• Waiting for consent: a licence for alterations or a planning application can take weeks, so a portable bridges the gap
• Listed or restricted buildings: where no outdoor unit will be approved, such as some listed terraces and estates
• Occasional use: a spare room used a few nights a year

If you go portable, choose a dual hose model if you can, keep the hose short and straight, and seal the window gap as well as you can. Run it with the door closed.

The planning and consent picture

Portables need no planning permission and no installer. Split systems do need thought. In England, a reversible unit that also heats can be permitted development on a house if it meets the size, siting and 37 dB(A) noise limits, while a cooling only unit always needs permission (Planning Portal). Flats are harder, because the right applies to a whole block and allows one unit. In Islington, the council lists 42 conservation areas, and many terraces are listed, so applications are common. Our Islington area page covers that in more detail.

The refrigerant in a split system is a fluorinated gas, so installation must be done by an engineer with an F-gas qualification working for a certified company. That is one reason splits cost more up front. Portables come pre sealed and need no engineer.

Cost

Portables are cheap to buy and nothing to install, but they use more electricity for the cooling you actually get. Split systems cost more because of the equipment, the engineer’s time and the electrics, but they cool more for each unit of electricity used. The Energy Saving Trust puts a typical single room air to air system, which is a reversible split, at about £1,900 (Energy Saving Trust). Your actual price depends on pipe length, outdoor unit access and the electrics.

What about all in one wall units?

There is a middle option. All in one, or monobloc, units fix inside on an outside wall and breathe through two holes about 15 to 20cm wide, with no outdoor box. They are stronger and neater than a portable, but louder in the room than a split, and they still need the building owner’s consent for the holes. We look at them in detail in our guide to air conditioning without an outdoor unit.

Our view

For a room you will use every summer, a split system is the right answer if you can get consent. Use a portable when you cannot fix anything, or while you wait for the paperwork.