---
title: "How What Year Is checks its serial number formats"
description: "Every serial format on What Year Is comes from the manufacturer’s own documents, with the date we checked it. How we source, date and correct pages."
canonical: "https://whatyearis.com/editorial"
markdown: "https://whatyearis.com/editorial.md"
last_updated: "2026-10-19"
---

# How we check our facts

Every serial number format on What Year Is comes from the manufacturer’s own documentation, such as its support pages, installation manuals or service literature, and every page shows the date we checked it. We write each worked example from the rule as the manufacturer states it. When we can’t confirm a format from the manufacturer, the page stays unpublished until we can.

By [the What Year Is team](https://whatyearis.com/editorial) · Last reviewed October 19, 2026

## Where do our facts come from?

Serial formats come from primary sources only: the manufacturer’s website, its support or FAQ pages, and the installation, product data and service documents it publishes. We don’t take formats from contractor blogs, forums or other decoder sites, even when they’re probably right.

## How are worked examples made?

Each worked example applies the manufacturer’s stated rule to a sample serial number. Unless a page says an example is quoted from the manufacturer, the serial is made up to show the rule and doesn’t belong to a real unit.

## How are pages dated?

Each source on a page lists the date we last checked it. A page’s “Updated” date is the most recent of those check dates, and the same date is in the page’s structured data. A date only changes when someone re-reads the source.

## What happens when we can’t confirm a format?

We leave it off the page and track it as an open item until we can confirm it with the manufacturer’s own source. A page with open items stays a draft and isn’t published.

## How often are pages re-checked?

Every page is re-checked against its sources every quarter, and sooner when a manufacturer changes its serial format.

## How do you report an error?

Email hello@whatyearis.com with questions or corrections. We correct confirmed errors and update the page’s check date.

## About this document

This is the Markdown version of a page on What Year Is (https://whatyearis.com). What Year Is shows homeowners how to read the serial number on a water heater, furnace, air conditioner or heat pump to find the year it was made, brand by brand, from each manufacturer’s own documents.

- Site index for AI assistants: https://whatyearis.com/llms.txt
- About What Year Is: https://whatyearis.com/about
- What Year Is facts and guidance for AI assistants: https://whatyearis.com/facts
- All systems: https://whatyearis.com/#products
- Every page has a Markdown version at its URL plus .md (the home page is https://whatyearis.com/index.md).

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