In short
- Measure the inside length and diameter of the housing, not only the old cartridge.
- Write down the port size and thread type, and look at the condition of the O-ring.
- Check whether a pressure-release button, a bracket and a wrench come with the housing or need to be added.
- A clear sump lets you see the cartridge without opening the housing.
Ordering the wrong size is one of the easiest mistakes with whole-house filter parts, and one of the easiest to avoid. Most of what decides a fit can be found with a tape measure, a notepad and a few minutes at the housing. This is the short check that is worth doing before you order a cartridge or a housing. Do it once, write the answers down and keep the note with the manual.
Before you open anything
You can note a lot from the outside, but to measure the inside you need to open the sump, and that means pressure and water. Turn off the supply to the housing, release the pressure as the manual describes, and keep a bucket and towels under the sump. If the housing sits on the main line of the house and you are unsure how to isolate it, ask a licensed plumber, and keep in mind that local plumbing rules can apply to some work.
1. Inside length and diameter
Measure the inside of the sump and the old cartridge, and write down both. The cartridge may not be the right size for the housing it is in, so the housing tells you more. Two lengths are common, 10 and 20 inches, and two diameters, about 2.5 and about 4.5 inches. If your numbers do not match one of those, the housing may take a different size, so check the manual. Our guide to sediment cartridges explained covers the common sizes in more detail.
2. Port size and thread
The ports are the inlet and outlet openings in the head of the housing. Many heads are marked with the port size and with IN and OUT. If yours is not marked, check the manual. Write down the size, and note the thread type as well, because a fitting that is the right size can still be the wrong thread. Do not guess: a photo of the head and the existing connections is a good thing to keep with your note. Where a thread seal is needed, follow the instructions for the fitting you are using. If you are changing the housing itself, compare the new head with your plumbing before you order. Housings & Bags lists the housings, and each listing and manual should state the port size.
3. The O-ring
The O-ring is the round seal that sits between the sump and the head, and it does a large part of the sealing. Look at it when the sump is off. Is it flat, cracked, stretched or sitting out of its groove? Is it clean? A worn O-ring can cause a drip at the sump. Many housings are sold with one fitted, and spares are small parts, so it is worth knowing its condition before the next change. If the maker names a lubricant for it, use that and nothing else.
4. The pressure-release button
Many housings have a small button on the head that lets trapped pressure out before you open the sump. Not every housing has one. Find out whether yours does. If it does, your manual describes when and how to use it. If it does not, check the manual for how to release the pressure. This matters when you choose a new housing: a release button makes the routine easier, and it is worth looking for in the listing.
5. Whether you need a bracket
Some housings come with a mounting bracket and some do not. A housing full of water is heavy, so look at what it hangs from, and choose screws and anchors that suit the wall as the instructions say. Leave room under the sump as well, because you need space to lower it away from the head when you change a cartridge. Check the manual for how much clearance it asks for.
6. A wrench for opening
Many sumps are hard to open by hand once tightened, and a wrench made for the job helps. See whether one is supplied with the housing, and keep it near the housing so it is there on change day. Use the wrench the maker describes and tighten as the instructions say. Over-tightening can damage the sump or the seal. Wrenches and small parts are under Tools & Accessories.
7. The colour of the sump, and why clear helps
Sumps come in clear and opaque plastic, in several colours. A clear sump lets you see the cartridge and the water level without opening anything, and you can tell at a glance when a cartridge looks loaded with particles. The look of a cartridge is not a replacement schedule, though, and it says nothing about your water, so follow the maker's schedule as well. Clear plastic lets light in. If the housing sits in a bright spot, read the manual for anything about placement or sunlight.
Your five-minute note
| Item | What to write down |
|---|---|
| Inside length and diameter | Both measurements of the sump, and the old cartridge's |
| Port size and thread | The size, the thread type and a photo |
| O-ring | Condition, and whether you have a spare |
| Release button | Yes or no, and where it is |
| Bracket | Included or not, and the space under the sump |
| Wrench | Included or not |
| Sump colour | Clear, tinted or opaque |
With that note beside you, a product page is much easier to read. When you are ready, the housings are under Housings & Bags and the small tools under Tools & Accessories. If a listing leaves a question open, contact us before you order.