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Guide

How often to change a furnace filter

There is no single magic number. Replacement depends on filter thickness, how loaded the media gets (MERV and household dust), pets or smoke, and how hard the system runs — including summer AC through the same slot. Use the thickness bands below, then check the panel and follow the brand sticker when they disagree.

Quick answer by thickness

These are typical consumer bands, not a guarantee for every home. Carrier’s residential guide and similar manufacturer pages put 1-inch filters in the 30–90 day range and thicker media cabinets at about 6–12 months. Many 1–2 inch pleated packs print ~90 days on the box.

If the manufacturer sticker or equipment manual gives a different interval, follow that. When unsure, pull the filter and look: gray, clogged, or collapsing pleats means replace now.

Why summer still counts

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

Heavy cooling seasons (long AC runtimes) load the filter the same way a hard heating season does. Do not wait for the first cold day to check it.

Change sooner if…

• Pets — hair and dander load media faster; multiple pets often need monthly checks.
• Wildfire smoke or poor outdoor air — fine particles fill the panel quickly.
• Renovation or construction dust — drywall and cutting dust can clog a filter in weeks; check every 2–4 weeks during the work.
• The filter looks gray or clogged — visual check beats the calendar.
• Weak airflow at vents, or the system struggling to hold setpoint — a dirty filter is a common cause.
• Manufacturer sticker / manual says a shorter interval than the table above.

Indoor smoking, frequent cooking smoke, or wood fireplaces also shorten filter life. We are describing equipment and airflow care here — not medical advice or health cures.

MERV and loading speed

Higher MERV captures a larger share of smaller particles and can load faster in a dusty or pet-heavy home, which raises airflow resistance as the panel fills. That is a fit-and-fan question, not a health-outcome claim. Pick a MERV your system can handle, then replace on schedule so the media does not stay packed. Details: MERV 8 vs 11 vs 13.

Measure and size first

A clogged filter does not help if the replacement is the wrong cut. Confirm printed size and brand actual dimensions before you reorder:

• How to measure a furnace filter
• 1-inch actual-size chart by brand
• Common money sizes: 16x25x1, 20x20x1, 20x25x1, 16x20x1
• Thicker media: 16x25x4, 20x25x4 · AprilAire: 210 vs 213

Where to buy

This guide does not list pack prices — those move daily. Open your size page for dated merchant tables, then buy the printed size and thickness that match your slot.

• 1-inch money sizes — 16x25x1 · 20x20x1 · 20x25x1 · 16x20x1
• 4-inch media — 16x25x4 · 20x25x4 · AprilAire 210 / 213
• All listed sizes — Size index

Full policy: disclosure.