01 / DOORS
Q-Lon weatherstrip replacement, and the one spec that decides whether it works
If the seal around your entry door has gone hard and shiny, this is almost certainly what it is. Buying the replacement is easy. Buying the right reach is the part people get wrong.
We earn a commission on some links here, at no extra cost to you. It does not change what we recommend or the order they appear in. How we are funded
Pull a few inches of the old strip out of the slot and look at how far the bulb stands off the spine. That is the reach, and it is what you are buying: medium is the common factory fitment, long is for a door that sits further from its frame. Match it. Fitting long reach where medium belongs stops the door latching.
What Q-Lon is, and why your door probably has it
If you have a prehung entry door bought in the last few decades, the seal running around the inside of the frame is a foam-filled compression strip pushed into a machined slot. Q-Lon is the name of the profile family that a very large share of those doors shipped with, which is why people arrive searching the brand rather than the category: they have pulled a piece out, seen the name or recognized the shape, and want the same thing back.
It fails in a specific and recognizable way. The foam inside loses its spring, so the strip stops pushing back; the outer skin goes hard, shiny and slightly brittle; and on the sunny elevation it may crack along the fold. The symptom is a door that looks shut and whistles anyway, usually worst on the latch side.
The good news is that this is a genuinely easy repair. The strip pulls out by hand, the new one pushes in by hand, and there is no adhesive, no tools and nothing to cure. The only way to get it wrong is to order the wrong part, which is what the rest of this page is about.
Why one reach is often wrong all the way round
This is the part almost nothing else in this category explains, and it is the reason one of the picks here is a deliberately mixed kit.
A door does not sit the same distance from its frame on all three runs. On the hinge side it is held in tight by the hinges themselves, and the gap there is small and consistent. On the lock side the door is only pulled in at one point, by the latch, so the gap above and below the strike tends to be wider. The header sits between the two.
So factory fitments frequently use a LONGER reach on the lock side and header and a SHORTER one on the hinge side. If you have ever fitted one reach all the way round and ended up with a door that latches fine but still leaks at the lock, or seals at the lock but will not shut without a shove, this is almost certainly what happened: you fitted a uniform strip to a door that was never uniform.
Match the part to your gap
Measure at the widest point. Then read across. If your measurement sits on a boundary, take the larger band — a seal that is slightly too big compresses, and one that is too small does nothing at all.
| Your gap | Part type | Our pick | Price |
|---|---|---|---|
| Whole door, medium reach, light frame | 3-piece kit, Medium Reach, Beige |  Q-Lon 96 in Replacement Kerf Weatherstrip Kit, Medium Reach, Beige, 3 PiecesThe common factory fitment. Hinge, lock and header matched in one order. | $39.95 · CHECK ON AMAZON |
| Whole door, medium reach, brown frame | 3-piece kit, Medium Reach, Brown |  Q-Lon 96 in Replacement Kerf Weatherstrip Kit, Medium Reach, Brown, 3 PiecesSame kit, the other color prehung doors actually shipped with. | $39.95 · CHECK ON AMAZON |
| Double doors, sealed on the hinge sides but not the middle | Kit, Long astragal and header, Medium hinge |  Q-Lon 96 in Replacement Kerf Weatherstrip Kit for Double Entry Doors, Long Reach Astragal and Header with Medium Reach Hinge Sides, BeigeA real factory configuration, and the fix when one reach is wrong everywhere. | $54.95 · CHECK ON AMAZON |
| One run only, gap has opened up | Single strip, Long Reach, Beige |  Q-Lon 96 in Replacement Kerf Weatherstrip, Long Reach, Beige, Single StripFor a side where the door has dropped away. Wrong if the gap is normal. | $23.95 · CHECK ON AMAZON |
| One run only, normal gap | Single strip, Medium Reach, Brown |  Q-Lon 96 in Replacement Kerf Weatherstrip, Medium Reach, Brown, Single StripThe lock side usually dies first. Cheapest correct answer when it does. | $23.95 · CHECK ON AMAZON |
Whole door or one run
Weatherstrip does not fail evenly, so buying for a whole door is not automatically the right call. Two patterns are worth recognizing.
The LOCK SIDE goes first on most doors, because it takes the compression every time the door closes and it is the run under the most load. A lock-side strip can be dead while the hinge side still springs back perfectly well. That is the case for a single strip, and it is much cheaper.
The SUNNY ELEVATION goes first across a house. If you have two exterior doors and one faces south, that one will need doing years before the other, whatever the catalog says about service life. UV is what hardens the skin.
Against that, a three-piece kit gives you three runs that match each other in color and age, which a patched door never will. If the doorway is prominent, that is worth real money. If it is a side door into a utility room, it is not.
Fitting it, which is the easy part
There is very little to this and it goes wrong in only two ways, both avoidable.
- 1Pull the old strip right out and clear the slot. Old weatherstrip leaves crumbs of perished foam in the kerf, and a new spine will not seat properly on top of them.
- 2Start at the top of a run and push the barbed spine in with a thumb, working down a few inches at a time. Do not stretch it as you go: stretched strip contracts over the following weeks and leaves you short at the bottom, which is exactly where you do not want a gap.
- 3Cut each run slightly long and compress it into the corner rather than butting it loose. A joint under light compression stays closed; a joint cut exactly to length opens as the strip settles.
- 4Shut the door and check it latches with normal effort before you do the second run. If it is already fighting you, the reach is too long and it is far better to find that out on one run than on three.
What we would skip, and why
Nobody in this category ever declines to recommend something. That is what makes universal praise worth ignoring. Here is what we would not buy.
Ordering before you have pulled a piece of the old strip out
It takes about ten seconds and it is the whole job. Get a fingernail under the strip in the kerf slot, pull a few inches free, and look at it. You are reading two things: how far the bulb stands out from the spine, which is the REACH, and what color it actually is under the dirt. Everything on this page is sold by those two attributes, and guessing at them is the only way to get this purchase wrong.
Fitting long reach all the way round because it seals better
It does not seal better, it reaches further, and those are different things. A longer reach on a door that only needed medium means the door is compressing more foam than it was built to, so it becomes hard to latch and people start slamming it. Slamming is what flattens weatherstrip permanently, so the over-specified strip fails faster than the correct one would have. Match the reach; do not upgrade it.
Buying Q-Lon for a frame with no kerf slot
All of this pushes into a machined slot around the door stop. If you run a finger along your stop and there is no slot in it, none of these parts has anywhere to go and no amount of adhesive will hold a barbed spine to a flat surface. That frame wants adhesive weatherstrip instead, and the decision is covered in best weather stripping for doors and, for prehung metal doors specifically, best weather stripping for steel doors.
Replacing one run and expecting it to match
It will seal correctly and it will not look the same. A new strip next to two that have had ten years of sun on them is visibly a different color, and this material cannot be painted to match. That is a perfectly reasonable trade when only the lock side has failed and money matters, and it is worth knowing before you open the package rather than after. If appearance matters more than cost, buy the kit.
Treating hardened weatherstrip as the whole problem
Weatherstrip that has gone hard is a real failure and replacing it is worth doing. But if the door has also DROPPED, which is common on an older prehung unit, new strip of any reach is being asked to cover a gap that is wider at the top than the bottom, and it will not. Check the gap at the top, middle and bottom of the latch side before ordering. If it varies a lot, the hinges want attention first and the strip second.
If the replacement does not fix it
New weatherstrip solves a hardened-seal problem and nothing else, so it is worth knowing what it does not solve before you decide it has failed.
It does nothing at the bottom of the door, where there is no frame to hold a strip. That gap is usually the largest single opening in the doorway, and it wants a sweep or a threshold instead: best door sweeps and best door thresholds cover the parts, and how to measure a door gap covers sizing them.
And it cannot correct a door that has moved. If the gap on the latch side is visibly wider at the top than the bottom, the door has dropped or the frame has racked, and a compression strip is being asked to span a wedge. Adjusting the hinges costs nothing and should come first. How to find drafts in your house covers confirming the door is actually where your air is coming in.
Complete the kit
The parts that decide whether the seal you just bought actually holds. Skip these and you will be doing the job again in March.
Removing old weatherstrip adhesive
Goo Gone Pro-Power Adhesive Remover Spray, 16 fl oz, with Scraper
The step everybody skips: the new tape will not stick to the residue the old tape left behind.
Medium frame gaps
Frost King EPDM Rubber Self-Stick Weatherseal Tape, D-Section, 5/16 in x 1/4 in x 17 ft
EPDM in a hollow D — the profile that keeps sealing at minus ten where foam tape has already gone hard.
Deep gaps before caulking
Frost King C21CP-C Caulk Saver Backer Rod, 3/8 in x 350 ft
Backer rod: the foam you push into a deep gap so the caulk over it is a seal rather than a bottomless hole.
#ad · how we are funded · price as of October 17, 2026
How we picked
- We rank on published reach first, because reach is the single specification that decides whether the replacement seals, and it is the one that generic kerf strip does not publish at all.
- Kit or single strip second, matched to how weatherstrip actually fails — unevenly, usually on the lock side and the sunny side first — rather than assuming everyone is doing a whole door.
- Color third, treated as a fitting decision. This material cannot be painted, so the color you order is the color in your doorway for the next decade.
- No maker publishes a working gap range for compression weatherstrip and we do not infer one; reach is the published spec and it is the right one. We did not test these. Prices come from the live price layer and are dated; the full method is published.
We have not tested these products and we do not claim to have. The full method, including what we refuse to claim, is on how we pick.
Questions people actually ask
- What is Q-Lon weatherstrip?
- A foam-filled compression weatherstrip that pushes into a machined slot around the frame of a prehung door. It is the profile family a very large share of prehung entry doors shipped with from the factory, which is why people search for it by name: they have pulled a piece out and want the same thing back rather than a generic substitute.
- What is the difference between medium reach and long reach Q-Lon?
- Reach is how far the foam bulb stands out of the slot to meet the door. Medium is the common factory fitment. Long stands further out, for a door that sits further from its frame. It is not an upgrade: fitting long reach where medium belongs means the door compresses more foam than it was designed to and becomes hard to latch.
- How do I know which Q-Lon reach I need?
- Pull a few inches of the existing strip out of the slot and look at it end-on, comparing how far the bulb stands off the spine. If the door currently latches with normal effort and simply leaks, order the same reach you took out. Check all three runs, because a lot of factory doors use a longer reach on the lock side and header than on the hinge side.
- Can I replace just one side of the weatherstrip?
- Yes, and it is often the sensible call, because the lock side takes the compression on every close and usually hardens years before the hinge side. The trade-off is appearance: a new strip beside two aged ones is visibly a different color and this material cannot be painted. If the doorway is prominent, buy the three-piece kit instead.
- Will new Q-Lon fix a door that still leaks at the bottom?
- No. Q-Lon seals the two jambs and the header, where there is a frame to hold it. The gap under the door has no frame and is usually the biggest opening in the doorway. That needs a sweep or a threshold, sized against the gap you measure, and it is a separate purchase from this one.
- Does Q-Lon fit any door?
- Only a frame with a kerf, the machined slot around the door stop. Run a finger along your stop: if there is no slot, a barbed spine has nothing to grip and adhesive will not hold it. The listings for these parts name Masonite, Jeld-Wen and Taylor entry doors as fitments, so the safest check is still to pull your old strip and compare the profile.
Read next
The best weather stripping for steel doors, chosen by what your frame actually has
Check the frame for a kerf slot and the slab with a fridge magnet. Those two answers pick the part.
The best weather stripping for doors, by published thickness
V-strip, D-section, silicone and foam placed against the gap each published thickness can actually seal.
The best door sweeps, sorted by the gap they actually close
Six sweeps placed by the gap they close, from a slim vinyl blade to a brush for uneven floors.
Foam, V-seal or silicone: which weather stripping your door needs
Three materials, three gap bands, one spec table. Choose by measured gap, not by shelf price.
How to measure a door gap properly
The index-card method, the three-point rule, and how to read your number against a published seal size.