You know that smell. The one that hits you when you flip the AC on after the rig’s been sitting in the driveway for three weeks. That musty, dusty, vaguely sweet aroma that means your RV air conditioner has been quietly collecting every piece of pollen, dog hair, and dead bug from here to the last campsite you visited.
I used to ignore it. Then I pulled the filter out of my rooftop unit and nearly gagged. It was gray-brown, matted down like a cheap bath mat, and I’m pretty sure something had tried to nest in the corner. That was the day I learned RV AC filters aren’t a ‘set it and forget it’ deal. They’re a consumable, like oil or tires or your patience at a Walmart parking lot.
The problem is finding the right replacement. Dometic wants twenty bucks for a piece of foam that costs them a dollar to make. Amazon listings are a minefield of ‘fits most units’ that fit absolutely nothing. And the universal rolls? You end up hacking at them with scissors in a dusty parking lot, praying the edges are straight enough to not let air bypass the filter entirely.
This one — the 16 x 40 x 1/4 inch job from a brand that barely has a name — came in at $12.99 for a two-pack. That’s the price of one Dometic-branded filter, and you get two. I ordered them with low expectations and a backup plan to return them. Six months later, I’m ordering my second set.
First Impressions: It’s Foam. It’s Cheap. That’s Fine.
Let’s not pretend this is high-tech gear. It’s open-cell polyurethane foam, 1/4-inch thick, cut into a 16 by 40-inch rectangle. That’s it. That’s the whole product. But the quality of the foam matters, and this stuff is noticeably denser than the flimsy white sheets you get in some universal packs. It’s got structure to it. You can squeeze it and it springs back. The 40 PPI (pores per inch) rating means it’s catching the fine dust, not just the big stuff.
The first thing I did was hold it up to the light. You can see through it, which is good — that means airflow isn’t going to be choked off. Some filters are so dense they turn your AC into a whisper. This one lets air move. That’s critical because a rooftop AC unit that struggles for air runs longer, works harder, and eventually freezes up the coils. I’ve dealt with that. It’s not fun.
I also checked the dimensions against my unit’s filter slot before cutting. The 16-inch width is pretty standard for most Dometic and Coleman rooftop units. The 40-inch length? That’s where it gets interesting. My filter slot is about 18 inches long, so I had to cut this down. But here’s the thing — the foam cuts clean with regular scissors. No fraying, no crumbling, no weird residue. You mark it, you cut it, you slide it in. Takes two minutes.
The ‘Cut to Fit’ Claim Is Actually True
Most ‘universal’ RV filters are a lie. They claim they’ll fit anything but they’re either too thick, too stiff, or made of that fiberglass crap that sheds particles into your living space. This one is foam, so cutting it isn’t a chore. I’ve used foam filters before where the cutting process left jagged edges that let unfiltered air sneak around the sides. Not this one. A sharp pair of scissors and a straight edge gives you a clean cut that sits flush in the slot.
I’ve also read reviews from people who just fold the 40-inch length in half or even in thirds to fit their shorter slots. The foam is flexible enough to do that without kinking. That’s a nice option if you don’t trust your measuring skills. Just fold it over and shove it in. It’ll still filter, just with more layers than you technically need. And since it’s only 1/4 inch thick, even doubled up it’s not going to block airflow.
The thickness matters more than you’d think. Some replacement filters are a half-inch thick or more, and they don’t fit the shallow channels in older rooftop units. The 1/4 inch spec here matches what most Dometic Penguin and Coleman Mach units actually use. I’ve seen people buy thicker filters and then complain they can’t get the return air grille to snap back into place. This one slides in without a fight.
Real-World Use: The Milk Jug Test
Look, I’m not a scientist. But I am a guy who’s been running this filter for months, and I’ve got a simple way to test if it’s working: take a clean water bottle, put your mouth on it, and try to suck air through the foam. Did that when I first got them. There’s resistance, but not suffocation. That tells you it’s catching particles without strangling your AC.
The proof came about six weeks in. I pulled the filter out during a routine check at a campsite in New Mexico — where the wind never stops and the dust is everywhere — and it was dirty. Like, visibly gray, caked with fine desert dust. But here’s the thing: the inside of the AC unit was clean. The coils behind the filter were spotless. That’s the filter doing its one and only job.
I replaced it with the second one from the pack and tossed the dirty one. At $6.50 per filter, replacing it every couple of months is cheaper than the $80 coil cleaning spray and the hour of labor you’ll spend if you let that dust cake onto the evaporator fins. I’ve cleaned those coils before. It’s a miserable job involving fin combs and cramped spaces and lots of cursing. A $6.50 filter every two months is way cheaper than my dignity.
The Smell Test
Remember that musty smell I mentioned at the start? That’s not just dust. That’s mold and mildew growing on organic matter trapped in the filter. When you run your AC, moisture condenses on the coils and drips down into the drain pan. If that moisture hits a filthy filter, you get a petri dish situation.
This foam doesn’t hold moisture like the cheap fiberglass filters do. I ran my AC hard during a humid stretch in Tennessee — the kind of humidity that makes you feel like you’re breathing through a wet sock — and when I pulled the filter, it was damp but not soggy. It dried out quickly once the AC cycled off. No smell. No mold. The foam is naturally resistant to that kind of growth, which is a huge plus for anyone who stores their rig for weeks at a time.
If you’re dealing with an existing smell issue, swapping the filter is step one. I had to go further last year — cleaned the coils, flushed the drain pan, and replaced the filter. The smell was gone. If you’ve got a persistent odor even after a fresh filter, you might need to look at a deeper issue, like the drain pan itself. I did a full write-up on that mess over here if you’re dealing with the same thing: RV Air Conditioner Cover. Not the same problem, but it’s the same part of the rig, and knowing what’s on your roof helps you troubleshoot faster.
Compatibility: What It Will and Won’t Work With
This filter is designed for the standard 16-inch wide return air grilles found on most Dometic and Coleman rooftop units. If you’ve got a newer Dometic with a filter that slides out from the inside ceiling grille, this is likely what you need. If you’ve got an older unit with a filter that clips in horizontally, you’ll need to check your measurements.
The length is the variable. At 40 inches, you’ve got enough material to cover most configurations. For shorter slots, you’ll trim. For the rare longer slot, you might need two filters to fill it, which is annoying but workable. You can also cut this to fit the side-mounted return grilles on some motorhomes. I’ve done it. Works fine.
One thing I’ll warn you about: if you’ve got a Dometic unit that takes the specific part number 3313107.103 or 3105012.003, this isn’t the direct replacement for that. That’s a different size and shape. I’ve used those before and they’re fine, but they’re a different beast. I did a review of those specific filters if you need the details: Acostop 6 Pcs RV Air Conditioner Replacement Filters. Different product, same principle — know your dimensions before you buy.
The Two-Pack Math
Twelve ninety-nine for two filters. That’s the whole pitch. If you’re replacing filters every 60 to 90 days during active camping season, that’s about twenty-six bucks a year. For comparison, a single Dometic-branded filter runs fifteen to twenty bucks, and a lot of those are just rebranded generic foam anyway.
Now, the included filters won’t last forever. The foam degrades with UV exposure and repeated washing. If you’re the type who tries to rinse and reuse filters, you’ll get maybe three or four wash cycles out of these before they start to lose their shape. But at this price, why bother washing them? Toss them, replace them, move on. Your AC will thank you with better airflow and lower run times.
I should note, though — I did wash one once. It survived the sink, air-dried overnight, and went back in service. It worked, but it wasn’t as stiff as a fresh one. The foam had softened slightly. Fine for a short trip, but I wouldn’t trust it for a long haul. Just buy the next pack.
What You Don’t Get
There’s no frame, no rigid plastic border, no fancy antimicrobial coating. It’s just foam. If you need a filter that fits a specific brand-name housing without any cutting, this isn’t that. You’ll need to measure and trim, and if you’re the ‘it must be perfect’ type, the hand-cut edges might bug you. They don’t affect performance, but they’re not laser-cut factory edges.
Also, this is not a HEPA filter. It’s not stopping smoke particles or ultra-fine allergens. It’s a pre-filter, designed to keep the big stuff off your coils. If you’ve got serious allergies or you’re camping in wildfire smoke season, you’ll want a secondary filtration system inside the rig. This is just the first line of defense.
And the packaging? It’s a plastic bag. Nothing fancy. The filters might arrive slightly compressed from shipping, but they puff back up to shape within a few minutes. Don’t panic if they look flat when you open the package. That’s normal.
The Installation Reality
Pop the ceiling grille off. On most units, there are four screws or a few plastic tabs that release the grille. The filter sits in a channel behind the grille, usually on the intake side. Slide the old one out, slide the new one in, put the grille back. If you have to cut, do it before you climb up there — measure twice, cut once, and don’t try to trim it while balancing on a ladder with the grille in one hand.
I’ve installed these in under ten minutes, including the cutting. The hardest part is getting the old filter out without dumping a pile of dust in your face. Pro tip: do this outside, and wear a cheap dust mask. The stuff that accumulates in there is nasty.
One thing I learned the hard way: don’t overtighten the grille screws when you put it back. These foam filters are forgiving, but if you crush the gasket around the grille, you’ll get air bypass and rattles. Snug is enough. Hand-tighten and stop.
The Verdict
For $12.99, you get two filters that work, fit after a simple trim, and keep your AC coils clean. The foam quality is solid, the airflow restriction is minimal, and the price means you can actually replace them on a schedule instead of waiting until the smell forces your hand.
I’ve spent way more on filters that fit worse and performed the same. I’ve spent way less on filters that disintegrated after a month of summer use. This is the sweet spot. If you’re tired of choking on dust when you flip on the AC, or you’re just tired of paying Dometic’s tax for a piece of foam, pick these up.
If you pick one up through the links here, I might get a small cut — doesn’t cost you extra and it helps keep the lights on.
RV A/C Filters Replacement 16 x 40 x 1/4 on Amazon
They’re in the drawer under my bed now. Two fresh ones, waiting for the next trip. When I pull the dirty one out at the end of this season, I’ll have a replacement ready, and checking the filter will take two minutes instead of an afternoon of scrubbing coils with a fin comb and wondering why I ever thought RVing was a good idea. That’s worth twelve bucks.