The Fix-It Playbook — Furnace Filter Flowchart | Free 1-Page PDF | 2026 Edition

High bill, weak airflow, or an icy coil? Check the $10 part first.

Two questions sort it. Has it been more than 30–90 days since the filter was changed? Then the light test: hold the old filter up to a light. No light through it means it's clogged; light through it points to the wrong size, the wrong MERV, or the wrong direction, three steps each.

The sheet also carries the MERV quick-read (8–11 is the sweet spot, 13+ can restrict airflow and ice the coil), and a plain line on when to stop and call a pro.

One page. Print it or keep it on your phone. Free instant PDF download, yours to keep.

If the tree sends you deeper: How to Choose & Change Your Furnace Filter ($6) adds the replacement-interval chart by filter type, the buy-in-bulk trick, and how the filter and coil work as a pair. All five heating and cooling guides come together as the HVAC Maintenance Kit ($14), and all 24 year-round guides are in the Core Library ($49).