Methodology

This page explains precisely how a number gets onto this site — and what would get it removed.

1. Sourcing

Every specification originates in manufacturer documentation: the installation manual, the service manual, or the official product specification sheet. Retailer listings, aggregator sites and forum posts are never used as a primary source. Where a manufacturer publishes conflicting figures across documents, we cite the installation manual and note the conflict on the page.

2. Recording

For each entry we record the document number, the page number, and the month it was read. Those three fields appear on the published page. If we cannot fill all three, the entry stays unpublished.

3. Publication threshold

An entry is published only when it is explicitly marked verified in our source data. Unverified entries are excluded from the build automatically and never reach the site. We would rather cover five models correctly than five hundred approximately.

4. Re-checking

Pages display the month of last verification. Entries are re-checked when a manufacturer revises a manual, when a reader submits a credible correction, or on a rolling annual cycle — whichever comes first.

5. Nominal versus actual

Air filters are labelled by nominal size, a rounded figure used for ordering, and manufactured to an actual size roughly half an inch smaller so the filter clears the slot. We publish both and always identify which one to order by.

6. Known limits

A manual describes a factory-standard installation. Real homes deviate: external filter racks, retrofitted media cabinets and modified return plenums all change the required size. This is why every page tells you to confirm against your existing filter before ordering. Where a model is especially prone to variation, we flag it in the page notes.

7. Use of AI

We use AI tools for drafting and copy-editing assistance. We do not use AI to source, infer or generate specifications. Every number on this site was read by a person from a manufacturer document, and every page is reviewed by a person before publication.

8. Corrections

If a published figure is wrong we correct the page and log the change on our corrections page with the date and what changed. We do not quietly edit and move on.