When it comes to keeping your home comfortable and your air clean, the humble furnace filter does a lot of heavy lifting. With so many options such as 1-inch vs 5 inch filters, different MERV ratings, and various replacement schedules it’s easy to get confused.
Let’s break it down so you can choose the right filter for your furnace and your home.
What Is a MERV Rating?
MERV stands for Minimum Efficiency Reporting Value, and it measures how well a filter traps airborne particles like dust, pollen, pet dander, and even smoke.
- MERV 1–4: Basic protection; catches large particles like lint and dust.
- MERV 5–8: Standard residential filters; great for most homes, catching finer dust and allergens.
- MERV 9–12: High efficiency; captures smaller particles, including some bacteria.
- MERV 13–16: Hospital-grade; exceptional air quality, but may restrict airflow if your system isn’t designed for it.
👉 Tip: A higher MERV rating means finer filtration, but that doesn’t always mean it’s the best choice for your furnace.
Why a 5-Inch Filter Is Better Than a 1-Inch Filter
Think of your furnace filter like a window screen. A thicker filter (like a 5-inch) has more surface area, which means:
- Better airflow your furnace doesn’t need to work as hard.
- Longer lifespan 5-inch filters can last 6 to 12 months, while 1-inch filters often need replacing every 1 to 3 months.
- Cleaner air more filter material traps more particles without choking your system.
Simply put: a 5-inch filter delivers better efficiency, better air quality, and fewer filter changes.
How Often Should You Change Your Furnace Filter?
How long a filter lasts depends on both its thickness and MERV rating, as well as your home’s environment. Here’s a quick guide:
Pro tip: Homes with pets, allergies, or continuous fan operation may need more frequent changes.

| Filter Size | Merv Rating | Change Every... |
|---|---|---|
| 1 Inch | 1 to 4 | 1 Month |
| 1 Inch | 8 to 11 | 1 to 2 Months |
| 1 Inch | 12 to 13 | 1 Month (Max) |
| 4 to 5 Inch | 8 to 11 | 6 to 9 Months |
| 4 to 5 Inch | 12 to 16 | 6 Months |
Why a High MERV Rating Isn’t Always Good for a One Inch Filter
A lot of homeowners assume “higher MERV = better filtration.” But when it comes to a 1-inch filter, that can actually cause more problems.
High-MERV 1-inch filters restrict airflow because they’re trying to trap fine particles in a very thin space. That can:
- Strain your furnace’s blower motor
- Reduce heating and cooling efficiency
- Cause uneven temperatures in your home
- Lead to early equipment wear or breakdowns
Unless your system was designed for it, stick with MERV 8 or lower for 1 inch filters as it’s the sweet spot for efficiency and airflow.
The Bottom Line
A clean, properly sized filter is one of the easiest ways to protect your furnace and improve your home’s air quality.
If you’re constantly replacing thin 1-inch filters, upgrading to a
5-inch media filter can save you time, money, and headaches — all while keeping your system running efficiently.
At Walchuk Heating & Cooling, we can help you upgrade to the right filter system for your furnace and ductwork. It’s a small change that makes a big difference in comfort, performance, and peace of mind.
