Ask each contractor to distinguish between included work and items still awaiting evaluation.
A proposal that retains a furnace should explain compatibility and condition. A proposal that replaces it should identify the venting and indoor work.
Compare the final customer amount only after understanding the scope and any rebate deductions.
Compare this scope across proposals.
Turn spoken assumptions into scope
Mark every item as included, excluded, an allowance, or still awaiting inspection. Cover demolition and disposal, access, equipment pads, refrigerant line sets, condensate drainage, gas venting, electrical circuits, disconnects, controls, filters, duct transitions, permits and startup. If conditions inside a wall or panel are unknown, record how a change will be priced and approved.
For each material exclusion, allowance or pending condition, request a fixed add price, a stated allowance or cap, or the written pricing and approval method. Put both proposals on the same included-work baseline before comparing totals.
Ask who pulls permits, who performs each trade, and what document closes the work. A useful completion record can include permit signoff, model and serial numbers, startup readings, control settings, warranty registration and the service contact.