20x4.5 Water Filter Cartridge: Reading the Size
Out of stock
A 20x4.5 water filter cartridge is 20 inches long and 4.5 inches across. It is a large cartridge, the kind that goes in a housing where water enters a home.
The size has to match the housing it sits in. This page explains how to read the two numbers, how to check your housing and old cartridge, and how to change one safely.
This filter is out of stock right now, so it cannot be added to the cart.
Length first, then diameter
In 20x4.5, the first number is the length of the cartridge, 20 inches. The second is its diameter, 4.5 inches. You will also see it written as 20 x 4.5, and searches often drop the dot, as in 20x4 5.
Both numbers matter. A cartridge with the same length but a 2.5 inch diameter is far thinner and will not fit a housing made for 4.5 inch cartridges.
Checking your housing
Housings are made for one cartridge size. Look for a model number or size on the housing cap or a label on the sump, then check it in the housing maker's manual. That listed size is what the cartridge must match.
The size on a cartridge is nominal. Measure the old cartridge too and compare it with the size the housing maker lists before you choose a replacement.
Changing the cartridge
- Shut off the water to the housing and release the pressure.
- Unscrew the sump with the housing wrench, keeping it upright.
- Lift out the old cartridge and note any markings on it.
- Rinse the sump and check the O-ring for cracks.
- Seat the new cartridge on the center post, screw the sump back on hand tight, then turn the water on slowly and check for drips.
After the change
Run some water through the new cartridge before you use it, following the flush steps on its box. Change it sooner if water flow slows down.
If you are not sure about the plumbing work, hire a licensed plumber.
Read your old filter
- Read the housing cap or label for its model or cartridge size.
- Measure the old cartridge: about 20 inches long and 4.5 inches across.
- Compare those numbers with the size the housing maker lists.
- Check that the new cartridge has the same length and diameter before you open the housing.
When to call a pro
If the housing cracks, leaks at the cap after you tighten it, or the shutoff valve will not close, stop and call a licensed plumber.
Questions
What does 20x4.5 mean on a water filter?
It is the cartridge size: 20 inches long and 4.5 inches in diameter.
Will a 20x2.5 cartridge fit a 20x4.5 housing?
No. The length matches but the diameter does not. A housing made for 4.5 inch cartridges needs a 4.5 inch cartridge.
How do I know my housing size?
Check the cap or a label on the housing for its model, then look up the cartridge size in the housing maker's manual. Measure the old cartridge to confirm.
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Keep reading
General information from the numbers on the filter, not a substitute for your system manual. Brand names are used only to show fit.