What goes into a furnace installation quote
Equipment type. A single-stage 80% AFUE gas furnace is the budget option and is common in Phoenix because heating hours are low. Two-stage and variable-speed furnaces cost more but improve comfort and airflow for the AC side, which runs far more hours.
Compatibility with your AC. The furnace houses the blower that moves cooled air in summer. If the new furnace's blower and the existing evaporator coil aren't matched, cooling efficiency suffers. A good installer checks this.
Venting and gas. Older homes may need updated venting or a gas line inspection. Rooftop package units bundle heating and cooling in one cabinet and require a crane for replacement.