Portable AC buying guide: single hose, dual hose or split

Portable air conditioners look similar in a product listing and behave very differently in a room. The biggest divide is not the brand or the BTU number; it is how the unit handles air. Get that right and the rest of the decision is easy.

The three types

Single-hose. One duct pushes hot condenser air outside. To replace that air, the unit pulls it from the room, which drops the room below outside pressure. That lower pressure draws warm, unfiltered air back in through doors and window gaps, so the unit fights itself. Single-hose units are the cheapest and simplest, and they are fine for small or shaded rooms with a good window seal. From about €239.

Dual-hose. A second duct brings outdoor air in to cool the condenser, then exhausts it. Room air is no longer used as condenser feed, so the negative pressure largely disappears and the unit reaches temperature faster in bigger, hotter rooms. It costs a little more to run per hour but holds a large room better.

Mobile split. The compressor and condenser sit in a separate outdoor module joined to the indoor unit by a thin refrigerant line. No hot duct in the room, no waste heat dumped indoors, and only a 2.7 cm line crosses the window. It is the quietest and most efficient of the three, and the easiest to vent through an awkward window. The trade-off is finding somewhere outside for the module, which is why it is sold as the renter-friendly alternative to a fixed wall split. From about €899.

If your room is above roughly 25 to 30 m², or your only window is tilt-and-turn or fixed, the air path matters more than the price. That is where dual-hose and split units earn their keep.

BTU and kW

European listings quote cooling capacity in both BTU per hour and kW. The conversion is fixed: 1 kW is 3,412 BTU/h, so a 2.6 kW unit is about 9,000 BTU and a 3.5 kW unit about 12,000 BTU. Do not buy on the BTU number alone. A bigger number in a single-hose unit with a leaky seal can cool less than a smaller, well-sealed dual-hose unit. Size to the room with the finder or the sizing method, then compare units in that class.

Noise

Noise is quoted in dB(A), and the gap between models is large. A quiet mobile split runs near 39 dB(A); a quiet premium one-box portable around 43 dB(A); a budget single-hose unit can sit above 60 dB(A) at full power. For a bedroom or a home office, the quiet figure is worth as much as the cooling figure. The finder asks whether quiet matters and ranks accordingly.

Refrigerant and the 2027 rule

Newer portables use R290 (propane), which has a global warming potential of about 3, against 675 for R32 and over 2,000 for the older R410A. From 1 January 2027, the EU’s F-gas rules require new plug-in air conditioners up to 12 kW to use refrigerant below a GWP of 150, which effectively means R290 for monobloc portables. An R290 unit bought now is aligned with where the rules are heading. R290 is flammable, but the charge in a sealed portable is small and factory-filled; keep the unit upright and follow the handling notes. More on this in the energy label guide.

A short checklist

• Match the cooling capacity to your room, not to the biggest number on the shelf.
• Prefer dual-hose or split for rooms above about 25 to 30 m², or for tilt-and-turn and fixed windows.
• Check the quiet-mode dB(A) figure if the room is for sleeping or working.
• Favour R290 to stay ahead of the 2027 rule.
• Budget for a proper window seal; on a single-hose unit it is the difference between rated and disappointing.

Ready to narrow it down? Run the finder and it will rank units that fit your room, window and budget.