What is the best window air conditioner?

A real air conditioner has a refrigerant compressor and can lower a closed room below the outdoor temperature, and it is rated in kW or BTU of cooling power. A fan only moves air and removes no heat. An evaporative 'air cooler' blows air over water, adds humidity, needs a window open, and cannot reach a set temperature. compare.ac lists only units with a genuine refrigeration cycle, so everything you see here is a real AC.

Running cost is driven by efficiency: CEER on window and portable units, and SEER2 on mini-splits. Higher is better on both, but they are separate scales and a SEER2 number cannot be read as a ratio against a CEER number. Directionally, an efficient inverter mini-split is the cheapest type to run, while a single-hose portable can cost roughly two to three times as much for the same comfort, because much of its capacity is lost back through the exhaust hose. For window and portable units that ENERGY STAR certifies, we go a step further and show an estimated dollars-per-year figure, taken from the model's published annual energy use (a DOE test that assumes about 750 hours of cooling a year) priced at the average US residential electricity rate. It is a standardized figure for comparing units, not a personal bill: your real cost depends on how much you run it, your local electricity rate, and your climate. Mini-splits are usually the most efficient of all but are rated on SEER2, so we do not convert those to a dollar figure, and a missing running cost is a data gap, never a sign a unit is worse.

For a split or multi-split, yes. There is no US law banning DIY installation as such, but under EPA Section 608 only a certified technician may open the refrigerant circuit, and the EPA states plainly that this includes connecting or disconnecting the pre-charged line sets sold with “DIY” mini-split kits. That is worth knowing, because it is the opposite of how those kits are usually marketed. Doing the refrigerant work yourself voids the manufacturer warranty and risks a dangerous, illegal release. A portable monobloc, and most window units, need no installer at all: they are factory-sealed, so you set the unit down or fit it in the window and run the exhaust yourself.

Noise is measured in dB(A). A quiet split indoor unit on a low setting can be around 19 to 25 dB(A), which is barely audible and fine for a bedroom. Around 30 to 35 dB(A) is a soft hum that most people accept in a living room. Portable monobloc units are usually 52 to 58 dB(A) because the compressor sits in the room with you, which is closer to a dishwasher and can disturb sleep. If quiet matters, a split almost always wins; if you only cool occasionally, a portable may be acceptable.