This type of furnace coil is commonly known as an “A Coil” because of its distinctive shape.
Commonly known as “evaporator coils” or “A Coils” due to their distinctive triangular shape, furnace coils play an important role in your split system.
Air conditioners and heat pumps both work by moving heat from one location to another. For both systems in the summer, this means taking heat from inside the house and moving it outside. This is accomplished with refrigerant. As the refrigerant moves through the evaporator coil inside your home, it absorbs heat. That refrigerant then travels outside, where the heat is expelled and the refrigerant is then cooled, starting the cycle over again.
Heat pumps, of course, are able to reverse that operation in the winter, pulling heat energy from outdoor air (it might not seem like it on a cold Chicago night, but there’s some ambient heat energy there!) inside and expelling cold air.
During the winter, as your furnace uses gas or electricity to generate heat energy, the furnace coil acts as a heat exchanger, absorbing that heat so that the blower can distribute it through your air ducts.