If you remember to do exactly one thing for your HVAC system this year, make it this: change the filter. It’s the single most important — and most ignored — piece of home maintenance. A clogged filter quietly costs you money every month and slowly kills the most expensive appliance in your house.

Why it matters

The filter sits between your home’s air return and the rest of the HVAC system. It catches dust, dander, and pollen so your blower motor and coils don’t have to. When that filter gets clogged:

• Your energy bill goes up. A dirty filter restricts airflow, so the blower works harder to move the same amount of air. Studies suggest a 15–20% increase in energy consumption is typical.
• Your air quality drops. The filter can’t catch what it’s already saturated with. Dust gets pushed back into the rooms.
• Your system wears out faster. Strained motors and frozen coils are the two most common reasons HVAC systems die before their time. Both are caused by — you guessed it — neglected filters.

A new filter costs $8–$25. A new HVAC system costs $5,000–$15,000. The math is not subtle.

How often to change it

A reasonable default: every 3 months. But the right cadence depends on your home:

• Pets: every 1–2 months
• Allergies or smokers: every 1–2 months
• No pets, light use: every 3–6 months
• Vacation home: every 6–12 months

If you can’t remember the last time you changed it, that’s your answer.

What to buy

Filters are rated by MERV (Minimum Efficiency Reporting Value). Higher numbers catch finer particles — but also restrict more airflow.

• MERV 8: standard, fine for most homes
• MERV 11–13: better for allergies, dust-heavy homes
• MERV 14+: hospital-grade, often too restrictive for residential systems

Stick with MERV 8–11 unless your HVAC manufacturer specifically supports higher. A too-restrictive filter creates the same problem as a clogged one.

Measure your current filter first — the size is printed on the cardboard frame (e.g., 16x25x1). Don’t trust the size you “remember.”

The actual steps

1. Turn off the system at the thermostat. You don’t want it pulling in dust while the slot is open.
2. Find the filter slot. It’s usually in the air return — a large vent in a hallway ceiling or near the furnace. Some systems have it inside the air handler itself.
3. Slide the old filter out. Note the airflow direction arrow printed on the frame.
4. Slide the new filter in with the arrow pointing toward the furnace/blower (away from the room).
5. Turn the system back on. Done.

Total time: under five minutes once you’ve done it once.

Set a reminder so you don’t forget

This is the part most people miss. Even when you do the swap, you’ll forget when. Two options:

• Calendar reminder: set a recurring 3-month event titled “HVAC filter.”
• Hank: this is exactly what we built it for. Add your home, tell us your filter size and how many people/pets live there, and you’ll get a notification when it’s actually time — not a generic checklist.

Common mistakes

• Wrong size. The filter should fit snugly with no air gaps around the edges. Air will take the path of least resistance.
• Wrong direction. The arrow points toward the system, not the room.
• Buying a higher MERV “just to be safe.” Often makes things worse for residential systems.
• Forgetting after one good attempt. Three months is the goal, not a one-time event.

That’s it. Five minutes, $12, and the rest of your HVAC system will thank you for years.