HVAC Air Filter Guide: What to Buy and How Often to Change It
The right air filter — changed on the right schedule — can extend your HVAC system life and improve your home air quality. Here is everything you need to know.
It's one of the simplest things you can do for your HVAC system — and one of the most commonly neglected. Changing your air filter on a regular schedule protects your furnace or heat pump, improves your indoor air quality, and keeps your energy bills in check.
Here's everything you need to know to do it right.
Why Air Filters Matter
Your HVAC system circulates all the air in your home multiple times per day. The air filter catches dust, pollen, pet dander, mold spores, and other particles before they reach the system's internal components.
A clogged filter restricts airflow, which forces your system to work harder. Over time, this leads to:
- Higher energy bills
- Overheating and short-cycling
- Premature wear on the blower motor and heat exchanger
- Poor indoor air quality
A clean filter, on the other hand, keeps airflow strong and your system running efficiently.
Understanding MERV Ratings
MERV stands for Minimum Efficiency Reporting Value. It's a scale from 1–16 that measures how effectively a filter captures particles of different sizes.
| MERV Rating | What It Captures | Best For |
|---|---|---|
| 1–4 | Large dust and debris | Basic protection only |
| 5–8 | Dust, pollen, mold spores | Most residential homes |
| 9–12 | Fine dust, pet dander, smoke | Allergy sufferers, pet owners |
| 13–16 | Bacteria, virus carriers | Hospital-grade; may restrict airflow |
For most Snohomish County homes, a MERV 8–11 filter strikes the right balance between air quality and airflow. Going too high (MERV 13+) can actually restrict airflow enough to strain your system — especially in older equipment.
How Often Should You Change Your Filter?
The right schedule depends on your home and lifestyle:
- Every 1–2 months: Homes with pets, allergy sufferers, or high dust levels
- Every 3 months: Average home, no pets, no allergies
- Every 6 months: Vacation home or rarely occupied space
When in doubt, check it monthly. Hold it up to a light — if you can't see light through it, it's time to change it.
Choosing the Right Filter Size
Filter size is printed on the side of your existing filter (e.g., 16x25x1 or 20x20x4). Always replace with the exact same size. A filter that doesn't fit properly allows unfiltered air to bypass it entirely.
Fiberglass vs. Pleated Filters
Fiberglass filters (the cheap blue or gray ones) have a very low MERV rating and need to be changed monthly. They protect the system but do little for air quality.
Pleated filters have more surface area, higher MERV ratings, and last longer. They cost a bit more but are worth it for most homes.
Avoid washable/reusable filters unless you're committed to cleaning them properly every month — they can harbor mold if not dried completely.
A Simple Reminder System
The easiest way to stay on schedule: set a recurring calendar reminder on your phone. Buy a 3-pack or 6-pack of filters at once so you always have one on hand.
Some homeowners write the installation date on the filter with a marker — a simple trick that makes it easy to see at a glance how long it's been in.
When a Filter Change Isn't Enough
If you've been keeping up with filter changes but still notice reduced airflow, higher bills, or uneven heating, there may be a deeper issue — a dirty evaporator coil, blocked ductwork, or a failing blower motor.
Our $69 diagnostic covers a full system inspection and can identify any issues before they become expensive repairs. Call 425-610-6635 to schedule.
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Snohomish Furnace & Air Team
Content creator and writer sharing insights and stories.
