Home / Seasonal change

Guide

Seasonal furnace filter change reminder

Spring and fall are useful calendar anchors for checking the same return filter that serves both furnace heat and central AC. They are reminders, not a hard rule: thickness, pets, smoke, and a clogged look still decide when to replace. Pair this page with how often to change a furnace filter for the thickness bands.

Why seasons help (heat ↔ AC, same slot)

Most homes use one filter slot for heating and cooling. When the thermostat calls for AC in summer, air still passes through that panel — the same way it does on a hard heating day. CNET’s year-round guidance is to replace typical thin filters at least every three months, including summer, or to use season changes as a reminder if you forget dates.

A spring check catches a filter that worked through winter heat. A fall check catches one that ran through summer cooling. Neither replaces looking at the media when it looks gray or airflow feels weak.

Spring / fall checklist

1. Find the slot — usually a return grille, furnace cabinet door, or media cabinet. Turn the system off before you pull the panel.
2. Read the printed size on the old filter (e.g. 16x25x1). If the print is gone, measure length, width, and thickness — see how to measure.
3. Check thickness — 1-inch pleats often land in the ~30–90 day band; 4–5 inch media cabinets are often ~6–12 months (Carrier-style residential bands). Details: how-often guide.
4. Look at the filter — gray, packed, or collapsing pleats means replace now, even if the season just started.
5. Note airflow direction — arrows on the frame point toward the blower / away from the return. Install the new one the same way.
6. Reorder before you need it — open your size page for dated merchant tables; do not guess the cut from a tape-only number.

If the manufacturer sticker or equipment manual gives a different interval, follow that. Visual check beats the calendar.

What to buy next

This guide does not list pack prices — those move daily. Use your printed size and thickness, then open a money page for current merchant rows:

• Top 1-inch sizes — 16x25x1 · 20x20x1 · 20x25x1 · 16x20x1
• MERV 13 comparisons — 16x25x1 MERV 13 · 20x20x1 MERV 13 · 20x25x1 MERV 13 · rating overview: MERV 8 vs 11 vs 13
• Thicker media / brands — 16x25x4 · 20x25x4 · Honeywell FC100A1037 · AprilAire 210 / 213
• Fit first — How to measure · 1-inch actual-size chart · How often (thickness bands) · All sizes

Full policy: disclosure.

When not to wait for a season

Do not park the calendar on equinoxes alone. Change (or at least check) sooner when:

• Pets — hair and dander load media faster; multiple pets often need monthly checks. Guide: pets and allergies.
• Wildfire smoke or poor outdoor air — fine particles fill the panel quickly. Guide: wildfire smoke: change sooner.
• Renovation dust — drywall and cutting dust can clog a filter in weeks.
• The filter looks clogged — gray, packed, or collapsing pleats beat any season reminder.
• Weak airflow at vents, or the system struggling to hold setpoint — a dirty filter is a common cause.

We are describing equipment and airflow care here — not medical advice or health cures. Thickness intervals and “change sooner if” detail: how often to change a furnace filter.