Start with the same written brief for each contractor: the equipment you have, the problem you want solved, the rooms or zones affected and any access restrictions. Note what you know and what still needs an on-site assessment.
Ask the proposal to identify equipment, included work, controls, electrical coordination, disposal, permits where applicable and exclusions. A replacement proposal should explain how the contractor assessed the building rather than simply copying an old equipment size.
Compare the commissioning and handover as well as the installation. Ask what measurements, settings, manuals and warranty documents you will receive. Keep manufacturer warranties and the contractor’s workmanship terms separate.
Agree how unexpected conditions and changes will be priced before work starts. Confirm credentials, insurance and local requirements directly; a directory listing or polished photograph is not a substitute for that check.