Windows and sun exposure significantly impact the BTU calculation because they contribute to heat gain in a room. Large windows or multiple windows allow more sunlight to enter, raising the temperature inside and increasing the cooling load. Rooms with windows facing direct sunlight, especially during peak hours, require a higher BTU rating to offset the added heat. It is recommended to add about 10% to the BTU calculation for rooms with substantial sun exposure. Additionally, using window treatments such as blinds, curtains, or reflective films can help reduce heat gain and improve cooling efficiency. Understanding BTU meaning in relation to windows and sun exposure helps in accurately sizing your AC unit. Properly accounting for these factors ensures that your air conditioner can effectively cool the space, maintaining comfort and efficiency.