Lennox 16x25x5 X6670 MERV 11 Box Replacement Filter for Lenn

The Verdict

If you own a Lennox Healthy Climate or Honeywell FC16 media cabinet, you already know the pain: this isn’t a standard 1-inch filter you grab at the hardware store. The 5-inch deep box filter is a specialty item, and the X6670 is the exact replacement Lennox designed for those systems. At 4.8 stars from 240 ratings, it’s clearly doing something right. But is it worth the premium over generic options? Let’s dig in.

What You’re Actually Getting

The X6670 is a 16x25x5-inch box filter with a rigid cardboard frame and MERV 11 pleated media. The “box” design is key — unlike standard filters that flex, this one has a sturdy outer frame that slides into your media cabinet and seals properly. The 5-inch depth means significantly more surface area than a 1-inch filter, which translates to lower pressure drop and better airflow even as the filter loads up with dust.

As shown in the product image, the filter has a directional arrow stamped on the frame, and the media pleats are tightly packed and uniform. This isn’t a flimsy aftermarket knockoff — the construction quality is immediately apparent when you handle it.

Real-World Performance

The MERV 11 rating is the sweet spot for most homes. It captures the stuff you actually care about — pollen, pet dander, dust mites, mold spores — without the airflow restriction you’d get from a MERV 13 or higher. That matters for your HVAC system’s efficiency and your energy bills. A higher-rated filter that chokes your system costs you more in the long run.

One buyer put it plainly: “Fits perfectly in my Lennox Healthy Climate system. No gaps, no air bypass. I’ve tried cheaper alternatives and they always let dust through the edges. This one doesn’t.” That’s the consistent theme across reviews — fitment is spot-on, and the filter does its job without drama.

The 5-inch depth also means you’re changing this less frequently. Under normal conditions, this filter lasts 6-12 months depending on your home’s dust load, pets, and how often you run your system. That’s roughly 2-4 times longer than a standard 1-inch filter, which partially offsets the higher upfront cost.

Where It Falls Short

Let’s be honest about the downsides. The biggest complaint is price — this filter typically runs $25-35 each, and there’s no bulk discount on this listing. If you’re buying several at once, you’ll feel it in your wallet. One reviewer noted: “Great filter, but I wish they offered a multi-pack. I ended up buying three and it stung.”

There’s also a minor concern about frame thickness. A few buyers mentioned the cardboard frame feels slightly less substantial than the original filter that came with their system. In practice, this hasn’t caused fitment issues for most people, but it’s worth handling carefully during installation to avoid crushing the corners.

Finally, this filter is only for systems that take 5-inch box filters. If you have a standard 1-inch filter slot, this won’t work — measure your existing filter before ordering.

Who Should Buy This

• Lennox Healthy Climate or Honeywell FC16 owners — this is the exact OEM replacement, and the fitment guarantee is worth the peace of mind
• Pet owners or allergy sufferers — MERV 11 gives meaningful filtration without sacrificing airflow
• Homeowners who forget filter changes — the 6-12 month lifespan is forgiving compared to 1-inch filters that need monthly attention

FAQ

Q: How often should I replace this filter? A: Every 6-12 months, but check it monthly. If you have pets or heavy dust, lean toward the 6-month end. If the filter looks dirty but airflow feels normal, you can stretch it further.

Q: Will this fit my Honeywell FC16 system? A: Yes. The X6670 is the direct replacement for the Honeywell FC16 series media cabinet. The dimensions and frame design are identical to the original.

Q: Is MERV 11 enough for allergies? A: For most allergy sufferers, yes. MERV 11 captures pollen, pet dander, and mold spores effectively. If you have severe respiratory issues, you might consider MERV 13, but be aware it will restrict airflow more.

The Verdict

Buy it if: You own a Lennox or Honeywell 5-inch media cabinet and want a filter that fits right the first time, filters effectively, and lasts up to a year.

Skip it if: You’re on a tight budget and willing to gamble on generic alternatives, or if you only need a 1-inch filter (this won’t fit).

Rating: 4.6/5 — It’s not cheap, but the OEM fitment, solid construction, and extended lifespan justify the premium for most homeowners.

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.