A horizontal air handler is a type of air conditioning system that is designed to provide efficient cooling and heating for residential and commercial buildings. It is a single unit that is mounted horizontally, usually on the roof or side of a building. The air handler contains an evaporator coil, a condenser coil, a blower, and a filter. The evaporator coil absorbs heat from the air inside the building and transfers it to the refrigerant inside the coil. The condenser coil then releases the heat to the outside air. The blower then circulates the cooled air throughout the building. The filter helps to remove dust and other airborne particles from the air before it is circulated. The horizontal air handler is an efficient and cost-effective way to cool and heat a building. It is also relatively easy to install and maintain.