Portable air conditioners — the wheeled free-standing units available from electrical retailers for £300-600 — seem like an attractive alternative to a fixed air conditioning installation at a fraction of the price. In practice, the comparison is less favourable to portables than it first appears. Here is an honest assessment.
How Portable Air Conditioners Work
Most portable air conditioners use a single exhaust hose that vents hot air through a window or door. The unit cools the air inside the room using a refrigeration cycle and exhausts the heat outside through the hose. Unlike a fixed split system (where both heat rejection and cooling happen outdoors and indoors respectively), the portable unit sits entirely inside the room and draws hot exhaust air from the room itself.
This creates an inherent inefficiency: the unit is pulling hot air from inside the room to exhaust through the hose, which creates negative air pressure in the room, which draws warm air in from outside or from other parts of the house through gaps around windows and doors. Some of the cooling you are paying for is immediately cancelled out by warm air ingress.
Performance Comparison
A well-specified portable air conditioner of 2.5kW nominal cooling output in a real-world UK environment will typically deliver effective cooling of 1.5-1.8kW — the remainder is lost to the single-hose inefficiency. A fixed 2.5kW split system in the same room delivers its full rated 2.5kW of cooling, often more on mild days due to inverter efficiency.
The practical difference: a fixed split system will cool a bedroom from 28°C to 21°C in approximately 20-30 minutes. A portable doing the same job takes 45-60 minutes and may not reach the same temperature on very hot days.
Energy Efficiency
Fixed split systems have SEER (Seasonal Energy Efficiency Ratio) values of 6-9 or higher — delivering 6-9 units of cooling per unit of electricity. Portable air conditioners have effective SEER values of 2-3 in real-world conditions, accounting for single-hose inefficiency. Running cost for equivalent cooling output: a portable air conditioner costs approximately 2-3x more per hour to run than a fixed split system.
Noise
Portable air conditioners are significantly louder than fixed split systems. A typical portable runs at 50-60dB(A) — clearly audible conversation level. A modern fixed split system at minimum speed runs at 19-25dB(A) — below the level of ambient room noise in most homes. For bedroom use, a portable air conditioner is typically too loud for comfortable sleep for most people.
When Portables Make Sense
Portables are appropriate for: temporary cooling in rented accommodation where installation is not permitted; emergency cooling while awaiting a fixed installation; cooling spaces that are used very infrequently and where the running cost premium is acceptable. For any permanent cooling requirement — a bedroom, home office, living room — a fixed installation is better in every practical respect except upfront cost.
The Cost Comparison Over 5 Years
Portable: £400 purchase + £200/year running costs (estimated) = £1,400 over 5 years. Fixed split system: £1,400 installation + £80/year running costs = £1,800 over 5 years. The 5-year total cost difference is £400 — for significantly better cooling performance, lower noise and greater reliability. Over 10 years, the fixed system is significantly cheaper.
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