The antonyms for the phrase "air cools" can be "air heats up" or "air warms". This means the temperature of the air increases instead of decreasing. When a room or a surrounding area is hot, people often use air conditioners so that the air can cool down, but when the weather is cold or the ambiance needs to improve, people use heaters or warmers. During the summer season, people avoid outdoor activities during the hottest part of the day when the air heats up, and they prefer staying indoors in the cool air-conditioned environment. In contrast, during winter, people love gathering around a warm fire or using a heater to provide warmth during the chilly season.