Do not confuse price with suitability
Ask why this model costs less. It could reflect equipment choice, purchasing arrangements, features, or work excluded from the quote. You cannot infer the reason from the total.
Then ask for the home's calculated heating need and the exact furnace output. Input is the fuel energy going into the furnace; output is the useful heat it delivers. Make sure those two numbers are not being compared as though they are the same. A proposed size needs a clear design basis.
ACCA's equipment-selection guidance uses heating and cooling loads, manufacturer data, and design conditions to choose equipment. ACCA Manual S overview.
Check ordinary operation as well as the coldest design conditions
If the model has two stages or other output control, request its lower and higher output levels. Ask how it will operate in milder weather and whether its controls are included. A large maximum output with a lower stage is not automatic permission to ignore sizing.
ACCA notes that oversized equipment can short cycle, meaning it starts and stops too often. ACCA sizing discussion. Do not assume that every short cycle has this cause or that every larger furnace will behave the same way.
Ask the bidder to explain the expected operation using the actual selection, rather than promising that a feature will compensate for any size. If there is a recurring cycling complaint now, include it in the assessment.
Confirm airflow and full project cost
Ask whether the blower and available air path can support the required heating and cooling operation. Request the commissioning plan, meaning the checks that confirm the installed furnace meets its setup requirements.
Compare the larger quote with a properly supported alternative using the same included work: controls, venting, drainage where applicable, electrical work, permits, removal, and follow-up. A cheaper furnace with an incomplete project is not yet a cheaper solution.
If the larger model fits the documented need and complete installation, the lower price may be worth considering. If it does not fit, an equipment discount is a poor reason to accept the mismatch. Ask for a suitable model at its actual full price.
Your next action is to request the load and selection explanation for both bids. Choose the fit first, then compare price among suitable projects. You should not have to guess whether the discount buys a problem.