Most filter slots take a size you can buy off a shelf. Some don't.
If you measured your slot and landed on 22.25 inches, or 19.75, or anything else sitting between the numbers a catalog stocks, you already know the problem. Round down and the gap lets air slip past the filter instead of through it. Round up and the filter won't seat. Neither one gives you a seal, and a filter that doesn't seal doesn't filter.
That's a custom slot, and it's more common than you'd think. Here's how we make a filter to fit it.
Three things hold true on every custom filter we cut:
±⅛″
How close we cut to the measurement you give us
Same media
Custom orders use the same filter material as our standard sizes
3 checks
Three people verify the size before your filter is packed
What "cut to size" means
We start with one of our standard filters in a size larger than the one you need, then cut it down to your measurements.
It's worth saying plainly, because "custom" gets used loosely in this category. Your filter isn't built one-off from raw material, and it isn't trimmed with a utility knife and taped back together either. It goes down a dedicated line with its own saw and its own capping station, and the size gets checked three separate times before it's packed.
We hold every custom cut to within plus or minus one eighth of an inch.
Your filtration level comes through the cut
Cutting a filter down changes its size, not its rating.
A filter's rating depends on the relationship between its face area, which is the opening air passes through, and its media surface area, which is the total pleated material doing the work. Cutting reduces both together, in proportion, and our custom process keeps that relationship the same. So the rating of the standard filter we start from is the rating of the filter you receive. Order MERV 11 in a custom size and you get MERV 11.
Face area and media area shrink in proportion
Standard size
9 pleats across the face
cut to size
Your size
7 pleats across the face
Narrower face, proportionally less media — the ratio holds, so the rating holds
A narrower filter has fewer pleats, but the same amount of media per inch of face. That's why the rating carries over.
MERV ratings are set by ASHRAE 52.2, the industry test standard, and that doesn't change when a filter is cut to size.
The material is no different either. Custom orders use the same filter media as our standard production, so there's nothing lesser about an odd size.
The five stations your filter passes through
Every custom order runs the same line, in the same order.
1
Ticket
Our customs lead prints your order and marks the pick ticket with the standard filter size that needs to be pulled and cut to reach your dimensions, then assigns the work.
2
Pick
A picker pulls that filter from stock and brings it to the saw.
3
Cut
The saw operator confirms it's the right filter, measures it before cutting, cuts it to your dimensions, and measures it again afterward to make sure the cut landed inside tolerance.
SIZE VERIFIED
4
Cap
The cappers check the size and the MERV rating again, then cut and apply the end caps evenly across the filter.
SIZE VERIFIED
5
Label and check
The labeler does the final size check, applies your label, and runs the last quality inspection before the order heads to shipping.
SIZE VERIFIED
That's three different people confirming the size before your filter leaves the floor, and it's deliberate. A standard size has a catalog number we can check against. A custom size has only your measurement, so we check the measurement three times.
How big we can make it
Most custom sizes are no trouble at all. The limit isn't the saw, it's the box: our largest custom filters are capped by what can ship as a standard parcel. If your measurements run past that, our custom team can talk you through the options.
Getting your measurement right
There's one part of this we can't do for you, and it's worth a couple of minutes of your time.
When a custom filter does need to come back, it's almost always because the measurement on the order wasn't quite right. That's the nature of made-to-order work. We cut to the number you give us, which is exactly the point, and it also means the number matters. So it's worth measuring carefully before you order.
Before you order
Measure the slot, not the old filter. An old filter can be warped or compressed, and it may have been the wrong size to begin with.
Measure all three dimensions. Depth is the one people forget, and it's the most common miss we see.
Don't round. Rounding to a nominal number is right for a standard size, but not for a custom one. Give us the actual measurement, down to the eighth of an inch.
Check it twice before you submit.
If you'd like a walkthrough, here's how to measure your air filter. It takes about two minutes, and it's the difference between a filter that seals and one that doesn't.
You have the measurement. We'll cut to it.
Enter your dimensions and choose your filtration level.
A custom filter starts as one of our standard filters in a larger size. Our customs lead marks the order with the size to pull, a picker brings it to the saw, the saw operator measures and cuts it to your dimensions, the cappers apply new end caps, and the labeler does a final check before it ships. The size is verified three separate times along the way.
Are custom filters cut down from standard filters?
Yes. We start with a standard filter larger than the size you need and cut it down on a dedicated custom line, holding the cut to within an eighth of an inch.
How do I know what size custom filter to order?
Measure the filter slot itself rather than the old filter, since an old one can be warped or may have been the wrong size. Measure length, width and depth in inches, and write down the actual measurement including any fractions.
Should I round my measurement to a whole number?
Not for a custom filter. Rounding to a nominal size is the right approach when you're ordering a standard filter, because standard sizes are cut slightly under their labeled dimensions. On a custom order we cut to the number you enter, so give us the actual measurement to the nearest eighth of an inch.
How precise is a custom cut?
We hold a tolerance of plus or minus one eighth of an inch on every custom filter.
Does cutting a filter to size change its MERV rating?
No. Cutting reduces face area and media surface area in proportion, and our process keeps that relationship constant, so the rating of the standard filter we start from carries through. MERV ratings are set by ASHRAE 52.2.
Do custom filters use different media than standard sizes?
No. Custom orders use the same filter media as our standard production.
What's the largest custom filter you can make?
The limit comes from shipping rather than from production. Our largest custom sizes are capped by what can go out as a standard parcel. If your measurements run past that, get in touch with our custom team.
