How often should you change your furnace filter?

Short answer: Follow the filter maker's interval, and check monthly. Thin 1-inch filters are often changed every 1 to 3 months; deeper 4-inch media filters have much more surface area and commonly last several months or longer. Pets, construction dust, wildfire smoke and heavy heating or cooling use mean changing sooner.

Step by step

1. Check monthly. Pull the filter and look at it against a light. If the media is grey and caked, replace it.
2. Use the maker's interval. The filter package and your furnace manual give the recommended interval.
3. Shorten it when needed. Change sooner with pets, renovation dust, smoke events or allergies.
4. Keep spares. Buying a multi-pack in your size makes on-time changes easier.

Multi-packs and 4-inch filters

• 16x25x1 Merv 11 Universal Air Filter By Tier1 (6-Pack) — $89.72
• 20x20x1 Merv 11 Universal Air Filter By Tier1 (6-Pack) — $62.48
• 16x20x1 Merv 11 Universal Air Filter By Tier1 (6-Pack) — $69.16
• 20x25x4 Merv 11 Universal Air Filter By Tier1 (Single Filter) — $95.16
• 20x25x4 Merv 13 Universal Air Filter By Tier1 (Single Filter) — $107.49

Common questions

What happens if I don't change my furnace filter?

A loaded filter restricts airflow, which can make the system work harder and reduce comfort.

Does a higher MERV filter need changing more often?

Finer filters can load faster in dusty homes. Check monthly and follow the maker's guidance.

Can I set up automatic filter deliveries?

Yes. Many of our filters can be set to auto-ship every 1, 2, 3, 6 or 12 months on the product page.

Shop HVAC air filters Choosing a MERV rating What size do I need?

Related categories: HVAC Air Filters. General information only; follow the equipment maker's instructions and local codes. Updated 2026-11-14.