Before you make an offer on a house, you can learn a good deal about its mechanical systems from paper the seller already has. The most useful item is the install year of each major system, because that year sets the planning clock you will inherit. Walk through the list below and collect what you can before you commit.
Start with heating. Ask what kind of unit it is, whether it burns fuel or moves heat from air or ground, and what year it was installed. Ask whether that install was a replacement or the original equipment. A replacement date and an original build date tell you different things. Compare the answer against the guides for the gas furnace, the boiler, and the heat pump so you know which age range you are walking into.
Then ask about cooling. Get the year of the outdoor condenser and the year of the indoor coil or air handler. These are often installed at different times, so note any mismatch. A coil that is newer or older than the condenser is a fact to write down. It is not a problem to solve on the spot. The central air conditioner guide explains how to read those years against a planning window.
Next, the electrical panel. Ask for the panel make, its install year, and whether any circuits have been added since. The electrical panel guide covers typical service life and when to plan for a change. Write down whatever the seller can give you, even if it is only a rough range.
Ask for records, not just answers. A seller who can hand you a permit card, an invoice, or a warranty document has given you a date you can check. A seller who guesses at the age has given you an estimate. Both are useful, but only the first is a record. Ask which one you are getting.
Also ask about the appliances that stay with the house, including the water heater and any system the seller has replaced. Built-in appliances carry their own install dates and their own planning windows. The appliance service life ranking is a good place to start when you build that list.
If the seller mentions a service plan or warranty, read it before you rely on it. A service contract is a general agreement, so check the coverage line, any waiting period before coverage starts, the cancellation rule, and whether the plan transfers to you at closing. A plan that cannot transfer is a different planning fact from one that can. Keep the paper with the house file.
Bring this list to your inspector. Ask them to note the apparent age of each system they see and to say where the house sits against the planning guides for that system. An inspector's note on age is a planning input, not a verdict. Put the dates in your file next to the offer, then decide what you will plan for in the first years you own the place.