Some warranties on a new system do not protect you from the day the equipment is installed. They begin only after someone files a registration, and the paper usually sets a window for that filing. Miss the window and the protection may never start, even though the equipment works fine.
Read the trigger before the window
Find the sentence that says what starts the coverage. Some papers count from the purchase date on the receipt. Others count from the install date, the date the unit was put into service, or the date the registration is accepted. Those dates can sit weeks or months apart, so the start point decides how much time you actually have. Copy the start rule onto the same page as the filing deadline.
Then find the window length in the paper's own units. Some give it in days, some in months, and some only refer to a separate notice. If the paper says the window is set out elsewhere, that other document is part of the contract and belongs in your folder.
Ask who files it
Ask the installer whether they register the unit for you or whether the filing is yours. If the installer files, ask for the written confirmation and the reference number that goes with it. If you file, ask whether the form is the manufacturer's own or a third party's, and whether the filing takes effect on submission or only after a later review.
Ask whether the registration carries over if the home changes hands, and whether a new owner must file again. The transfer rules are a separate question from the window, so read both.
Keep the proof of filing
Keep the confirmation page, the email, or the mailed acknowledgment. Save a copy in the same folder as the install record and the receipt. A filing you cannot show is hard to rely on later, and a verbal statement that you filed on time may not be accepted.
Check that the serial and model on the confirmation match the plate on the unit. A typo in either can leave the filing pointed at a different machine. If you see a mismatch, correct it while the window is still open.
If the window has already closed
Read the paper for a late filing route. Some documents allow a late registration on a stated condition, and some do not. Do not assume either way. Ask the seller or the manufacturer's service line directly, and get the answer in writing.
Where the figures live
This guide does not list any company's window length or coverage terms, because those change by product and by paper. Read the document you were given. For the planning side of a new install, the lifespan pages on this site turn an install year into a planning date, such as the gas furnace page. They do not replace what the warranty promises.