Equipment efficiency is only one part of performance. Sizing, controls, airflow, distribution, insulation, operating patterns and maintenance also shape the result.
Start with the actual system
Useful decisions come from the property, equipment and operating conditions rather than a generic answer. Record what the system is doing, when the issue occurs and what changed before the problem began.
Confirm the scope in writing
A written scope should identify the proposed work and the assumptions behind it. Ask which items are included, which conditions could change the work and what support applies after completion.