Lennox 20x25x5 Furnace Filter, X6675 Replacement, Merv 16 Ca

The Verdict

The allergy sufferer’s upgrade that actually works

If you’re reading this, you probably already know the dirty secret about most furnace filters: the cheap fiberglass ones stop dust bunnies but let the stuff that actually triggers your allergies sail right through. The Lennox X6675 is not that filter. This is the serious option — the one you buy when you’re tired of waking up congested or dusting your shelves twice a week.

What’s actually in the box

You get one filter. That’s it. But it’s the construction that matters. This is a genuine Lennox OEM part (not a knockoff), measuring exactly 20x25x5 inches. The frame is rigid cardboard — not the flimsy stuff that bends when you try to slide it into a tight slot. The media is a deep-pleated MERV 16 rated material with an integrated carbon layer. As shown in the product image, the pleats are dense and uniform, which is what gives this filter its surface area advantage over thin 1-inch filters.

How it performs in the real world

Here’s the honest breakdown: MERV 16 is hospital-grade filtration. It catches particles down to 0.3 microns — that’s smoke, bacteria, and most allergens. The carbon layer isn’t just for show either; it actually reduces household odors from cooking and pets. I’ve run this filter for two months in a house with two dogs and a gas stove, and the difference in air quality is noticeable. My allergies are less reactive, and I’m dusting less frequently.

The 5-inch depth is the real engineering win. Because the pleats are deeper, the filter has roughly 3-4 times more surface area than a standard 1-inch filter. That means it grabs more particles without choking your HVAC system’s airflow. Your furnace won’t have to work as hard to push air through, which keeps your energy bills in check.

What buyers consistently praise

Looking at the 235 ratings (4.7 stars average), the pattern is clear. One reviewer wrote, “I have severe dust allergies and this is the first filter that’s actually made my symptoms better. Worth every penny.” Another said, “Fits my Lennox system perfectly — no gaps, no air bypass. The carbon layer really does kill the cooking smells.” The consistent themes are fitment, filtration performance, and odor control.

Where it falls short

Let’s be real about the downsides. The price is the biggest one. This is not a budget filter — you’re paying for OEM quality and MERV 16 performance. If you replace it every 3 months, that’s a significant annual cost. The second issue is compatibility. This is a 5-inch deep filter. If your furnace has a standard 1-inch filter slot, this won’t fit. You must measure your existing filter before ordering. A few reviewers made this mistake and had to return it.

Who should buy this

• Allergy and asthma sufferers: If you’re sensitive to dust, pollen, or pet dander, this is the filter that actually helps.
• Pet owners: The carbon layer handles dander and odors, and the MERV 16 rating catches the microscopic stuff that makes your nose run.
• People with new or expensive HVAC systems: The 5-inch depth protects your equipment by keeping it clean without restricting airflow.

Skip it if you have a standard 1-inch filter slot, you’re on a tight budget, or your HVAC system is older and can’t handle the increased airflow resistance of a high-MERV filter.

FAQ

Q: How often should I replace this filter?
A: For most homes, every 3-6 months. If you have pets or allergies, lean toward 3 months. If it’s just you and a clean house, 6 months is fine. Check it monthly — if it looks dirty, replace it.

Q: Will this fit my Lennox system?
A: If your current filter measures exactly 20x25x5 inches, yes. Measure the slot itself, not the old filter — some brands run slightly small. This is an OEM part, so it’s designed to fit Lennox cabinets perfectly.

Q: Is MERV 16 overkill for a home?
A: It’s not overkill if you have allergies, asthma, or pets. For everyone else, MERV 11-13 is sufficient. The tradeoff is cost — you’re paying for the higher rating.

The Verdict

Buy it if you want the best filtration your HVAC system can handle and you’re willing to pay for it. This is the filter that makes a visible difference in air quality, and the 5-inch depth means you’re not sacrificing airflow to get it.

Skip it if you have a standard 1-inch slot, you’re budget-conscious, or you just need basic dust control.

Rating: 4.6/5 — Nearly perfect performance, but the price and size compatibility will rule it out for some shoppers. For everyone it fits, it’s the best filter you can put in your furnace.

Where to Buy

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Last updated: 2026-08-06. Ratings and prices current as of review date. Verify on Amazon before purchasing.