- Horizontal gas furnace
- Package gas furnace: also comes with an air conditioner
- Upflow gas furnace: airflow enters the bottom, and the heated air exits the top
- Downflow gas furnace: opposite of the upflow, airflow enters the top, and the heated air exits the bottom
- Lowboy gas furnace: shorter units designed for tight spaces
5. Furnaces can have a long life! With regular preventative maintenance, your furnace could last up to 25 years. On average, conventional furnaces last 18-25 years while high-efficiency furnaces have a slightly shorter life of 15-20 years.