Depending where you live and the standards of practice your home inspector uses, he/she should give you some information on your HVAC system. What you get in the report will vary between inspectors of course. Typical data in the report includes, but is not limited to: manufacture name, estimated age of the system, energy sources, etc. If you have ever wondered where this information comes from, every system should have a legible data tag. The example in the above photo is from a condenser unit cabinet, mounted outside of the house I recently inspected.
I use the website buildingcenter.org and the serial number on the data tag to find the age. Buildingcenter.org has a great search function for finding ages of HVAC units and water heaters.
The model number can be used to reveal useful information as well. For this particular Bryant unit, a quick google search using the first 10 digits of the model number revealed great information. The first available option from the search results happened to be the installation manual for this exact unit! The second page of the manual has a legend that breaks down the model number into usable information.
If you ever have any issues with the system and need to call a service company, the information on the data tag will be important to help expedite the repair or answer any questions you have about the system.