A useful central-air proposal names the complete system and the work that makes it function in the house. The total alone cannot show whether two proposals describe the same project.
Equipment selection
Look for the indoor and outdoor model numbers, matched-system information and controls. Ask what load calculation supports the capacity selection. ENERGY STAR advises using the actual characteristics of the home instead of a rule of thumb.
Air distribution
For existing ducts, ask what evaluation and corrections are included.
For new ducts, the proposal should define the served rooms and the supply and return strategy. It should state how the ducts will be sealed and balanced.
ACCA identifies Manual J for residential load calculations.
Manual S covers equipment selection. Manual D covers duct design.
Connections through the house
The scope should identify the refrigerant-line route and condensate drainage.
It should show the electrical circuit and disconnect. Equipment supports should also appear.
Ask who handles permits or work by other trades.
Clarify how any reused lines or wiring will be verified.
Startup and operating instructions
Treat startup as a named part of the quoted central-air scope. The proposal should say how airflow and refrigerant charge will be checked against manufacturer requirements and which results will be handed to you. If one total includes those checks and another proposal is silent, mark the second scope unclear before comparing the amounts; do not assume the two prices cover the same completion work.
Compare omissions as well as inclusions
One proposal may include duct correction, electrical work or finish repair that another excludes. Mark each item as included, excluded or unclear before comparing totals. A lower number can describe a smaller scope.