BTU SizerWindow vs Portable vs Mini Split
For a single room there are three realistic machines, and the choice is usually made on installation constraints rather than performance. It is worth knowing what each constraint costs you.
The short version
| Window unit | Portable | Mini split | |
|---|---|---|---|
| Typical cost | $150–500 | $300–700 | $2,000–5,000 installed |
| Install | Yourself, an afternoon | Out of the box | Licensed installer |
| Delivered capacity | Full label value | 60–70% of old-style ratings | Full, and modulating |
| Noise indoors | Loud — compressor is in the room | Loudest — compressor plus fan | Very quiet |
| Efficiency | Moderate | Lowest | Highest |
| Window | Blocked | Partly blocked by hose kit | Untouched |
| Heating too? | Rarely | Some models | Almost always |
Why the portable loses capacity
A portable stands inside the room it is cooling. Two things work against it. Its condenser heat leaves through a hose that runs hot across the floor and radiates part of that heat straight back into the room. And a single-hose model takes the air its condenser needs from the room, which means the house pulls in an equal volume of hot outside air through every gap to replace it.
Since 2017 the US label has been honest about this: SACC measures the unit as installed and comes out at roughly 60 to 70% of the old ASHRAE figure. Which is why the portable calculator allows about 30% more capacity per square foot than the window one.
A dual-hose portable fixes half the problem by feeding its condenser with outside air, and scores measurably better.
When each one is right
Buy a window unit when the window can take one and you are not fussy about noise. It is the cheapest cooling per BTU by a wide margin, and its rating is honest.
Buy a portable when a window unit is impossible: a casement or sliding window, a rented flat where nothing may be fitted, a listed building, or a room whose window is a fire escape. Pay the extra for dual-hose, keep the exhaust short and straight, and seal the window kit properly — a leaky kit undoes the whole machine.
Buy a mini split when the room matters for years rather than summers. It costs several times more, needs an installer, and pays it back in three ways: an inverter compressor that modulates instead of cycling, so the room holds temperature and the humidity stays down; near silence indoors; and heating in winter at two and a half to three and a half times the efficiency of any electric heater.
The one comparison people get wrong
A portable and a window unit with the same BTU number on the box are not the same machine — and a listing quoting a large BTU figure with no mention of SACC is almost always using the old scale. Size the room first with the calculator that matches the machine, then compare: window · portable · mini split.