Identify the complete control system
Gather the thermostat model, interface-module model, installed heating and cooling models, and the accessories controlled by the system. Use existing records or labels accessible without opening energized equipment. Include wireless room sensors, outdoor sensors, humidifiers, and other controlled devices if present.
For a concrete example, Honeywell Home's T10/T10+ documentation says the EIM and wireless outdoor sensor can connect only to the T10+ within that product family. It also lists sensor compatibility limits. The names are close, but the supported combinations differ. Honeywell Home exact interface compatibility.
That example does not establish compatibility with a different RedLINK generation or another manufacturer.
Compare replacement with conversion
Ask the manufacturer's support team or a qualified installer for the supported replacement list. If there is a direct replacement, ask whether configuration or accessory relinking is needed and who will complete it.
If the proposal removes the module or converts the equipment to another control system, ask what changes, which functions remain, and which are lost. The scope may include cable work, setup, or changes beyond the wall thermostat. Do not assume a retail thermostat is a simple substitute for a communicating control.
Google's Nest guidance identifies proprietary systems as a separate compatibility issue and notes that some need manufacturer-supported adaptation or professional conversion. Google proprietary-system limits.
Require a finished function record
Ask for the agreed controls and accessories to be checked after the work. Include heating stages, cooling if installed, fan settings, and sensor selection where applicable. Keep the final model numbers and configuration record for future repairs.
Your next step is to request an exact thermostat/module compatibility statement and a full installation scope before purchasing. That keeps the decision tied to the system your home actually uses.