The short answer
A fixed split system cools better, runs more quietly and can heat efficiently, but needs professional installation and somewhere for the outdoor unit. A portable suits occasional hot spells, renters and homes where a fixed system isn't possible.
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The choice mostly comes down to how often you'd use it, how much noise you can live with and how much you're able to change your home. A portable can be a sensible stopgap for a few hot weeks, while a fixed system is a long-term addition that heats as well as cools.
At a glance
| Fixed split system | Portable | |
|---|---|---|
| Cooling | Strong and steady | Weaker, especially single-hose |
| Noise in the room | Quiet, compressor outside | Louder, compressor in the room |
| Heating | Yes, as a heat pump | Some models only |
| Installation | Qualified engineer | Set up yourself |
| Permissions | Planning conditions, landlord or freeholder | Usually none |
| Windows | Close normally | Hose through a gap |
| Moving home | Stays with the house | Comes with you |
When a portable makes sense
- You only need cooling for a few hot days or weeks each summer.
- You rent, or live in a flat where fixed equipment isn't allowed or would take time to agree.
- You want to cool one room at a time and move the unit around.
- You need something straight away.
- You can live with more noise and a hose through a window.
If you choose a portable, a dual-hose model draws less warm air into the room, and sealing the gap around the hose helps. Portable air conditioners covers the details.
When a fixed system makes sense
- You own your home and plan to stay.
- You'd use it through the summer, and for heating in spring, autumn and winter.
- The room is a bedroom or home office where noise matters.
- A room overheats badly, such as a loft room or top floor, and needs cooling through long hot spells.
- There's a suitable place for the outdoor unit.
A wall-mounted split is a common choice, and there are other fixed types for rooms where one won't fit.
Permissions and practicalities
In England, a fixed system can usually be fitted without planning permission under permitted development, if the conditions are met. They include one heat pump on a house that isn't detached, the MCS 020(a) noise limit for neighbouring homes, and not using an air-to-air system solely for cooling. Listed buildings need listed building consent, conservation areas have stricter rules, and flats follow different rules, so check with your local council. Scotland, Wales and Northern Ireland have their own rules, and the planning permission guide sets out the conditions.
There's more to arrange for a fixed system:
- A split system's refrigerant circuit is connected on site, which needs an engineer with the right F-gas qualification.
- Most systems need a dedicated circuit from the consumer unit. In England and Wales, a new circuit is notifiable under Part P of the Building Regulations.
- In a rented or leasehold home, you'll usually need the landlord's or freeholder's permission.
A portable isn't a fixed installation, so the planning rules don't apply, and it plugs into an ordinary socket. A window left partly open for the hose is worth thinking about for security.
Comparing running costs
The same method works for any air conditioner. Multiply the power it draws in kilowatts by the hours it runs to get the energy used in kilowatt-hours (kWh), then multiply by your electricity rate.
For example, a unit drawing 0.8 kW for 5 hours uses 4 kWh. At an example rate of 25p per kWh (check your own tariff), that comes to £1.
Power draw rises and falls as a unit works harder or eases off, so treat this as a rough guide. Most fixed systems have an inverter that slows the compressor once the room is cool, while many portables simply switch their compressor on and off. When comparing models, look at their efficiency ratings as well as the power figure. Air conditioning running costs goes into more detail.
Other options
- Through-the-wall units are fixed and need no outdoor unit, but like a portable they have the compressor in the room, so they're noisier indoors than a split.
- Evaporative air coolers aren't air conditioners. They use little electricity, but they add humidity and do little on humid days.
Related guides
- Portable air conditionersA portable air conditioner is a self-contained unit on wheels that cools a room and sends the heat outside through a hose, usually out of a window. It needs no professional installation, but it is noisier and less effective than a fixed split system.
- Wall-mounted split systemsA wall-mounted split system pairs an indoor unit fixed high on a wall with an outdoor unit outside, joined by refrigerant pipes. It is a common choice for fixed air conditioning in UK homes, and most models heat as well as cool.
- How much does air conditioning cost to run?Multiply the electricity it uses, in kWh, by your unit rate. How much a unit uses depends on the room, the weather, the temperature you set and its efficiency, so estimate it from its average power draw and the hours it runs.
- Do you need planning permission?Usually not in England, where air-to-air heat pumps that aren't used only for cooling count as permitted development if conditions on number, size, position and noise are met. Listed buildings, flats and protected areas follow different rules.