Separate the heating job from the cooling job
A home load calculation addresses heating and cooling needs. Selecting equipment then uses performance data for the proposed combination. ACCA design and equipment-selection explanation.
If the contractor says “you need a bigger furnace for AC,” ask what “bigger” means. More fuel input? More delivered heat? A blower that can move the needed air? A different cabinet or approved equipment combination? Each answer leads to a different comparison.
For example, Daikin's DM96VC specification sheet lists heating data and cooling airflow information separately. That model is an illustration, not a recommendation for your home. Daikin DM96VC specifications.
Resolve any input and output confusion
Input is the fuel energy going into the furnace; output is the useful heat it delivers. Ask for the old furnace's stated input and output, the proposed model's input and output, and the calculated home heating need. Do not compare an old output number with a new input number and conclude the furnace is larger.
Ask the contractor to show the cooling equipment and required blower performance for the actual setup. That includes the indoor coil, outdoor unit, controls, and the air-distribution conditions relevant to the design.
A furnace can be proposed because a particular available combination meets the cooling requirements. The bidder still needs to explain whether its heat output also fits. Ask whether another compatible choice could meet both needs without unnecessary heating size.
Keep other work and limits visible
If existing airflow cannot support the AC design, ask what correction is required and who would provide it. Do not let that become a promise that a higher heating capacity alone fixes the air path. Confirm any other-trade scope separately; an equipment discussion does not establish a duct-work offer from MGI.
Request the full installed price and the startup checks for heating and cooling. Ask how the contractor will demonstrate normal operation and leave a record of the settings and findings.
A larger furnace may be justified in a particular project, but the explanation should connect to actual selection evidence. “We always move up a size when adding AC” is not enough.
Your next action is to ask for two separate written answers: why the proposed furnace fits winter heating and why its blower fits the AC design. Decide once both are supported.