Filters & Systems
HVAC Filter Replacement Calculator
How often should you change your air filter? Get a personalized replacement schedule based on filter thickness, pets, allergies, and home use. Free, no signup.
Frequently asked questions
How often should I change my HVAC filter?
A 1-inch filter typically lasts 1–3 months; a 4-inch filter 6–9 months; a 5-inch media filter up to a year. Pets, allergies, and heavy system use all shorten those intervals. The calculator above tailors it to your home.
How long does a 4-inch furnace filter last?
Usually 6–9 months for an average home. With pets or allergy sufferers, lean toward the shorter end and check it at the halfway point — a clogged filter strains the system and raises energy use long before it looks dirty.
Does a higher-MERV filter need changing more often?
Higher-MERV filters capture more, so they can load up faster and restrict airflow sooner if your system isn’t designed for them. Check a high-MERV 1-inch filter monthly; thicker media filters handle higher MERV without changing as often.
How often should I change my filter with pets?
Pet hair and dander load a filter quickly — with one pet, shorten the interval by roughly 20%; with several, by a third or more. For a 1-inch filter and multiple pets, that often means monthly.
What happens if I don’t change my furnace filter?
A clogged filter restricts airflow, making the system work harder, run longer, and cost more — and in extreme cases it can overheat the furnace or freeze the AC coil. Worse air quality and a shorter equipment life are the slow costs.