A wall-mounted air conditioner indoor unit includes a housing having a front housing and a rear housing, main air intake portions formed on the housing, a mixed air outlet formed on a lower portion of the front housing, a non-hot exchange air inlet formed on the rear housing, and an air delivery apparatus disposed inside the housing. The hot exchange air passage has an upper portion with a size greater than that of its lower portion. A volute and a centrifugal fan located inside the volute are disposed inside the housing and above the air delivery apparatus. An air output portion of the volute faces the hot exchange air passage, and includes a surrounding portion extending to the air delivery apparatus and surrounding the hot exchange air passages, and air mixed cavities are formed between the surrounding portion and the hot exchange air passages.