Chiller Filter Cartridges: Sizing, Cleaning, Replacing

Choose a cartridge by micron rating and flow, not by brand: a coarse pleated cartridge for general debris, a finer one only if the pump has headroom. Clean from the inside out, replace when flow stops recovering, and keep one spare so you never run the loop without filtration.

Filter cartridges are the cheapest consumable in a chiller loop and the one most often chosen by whatever was already in the housing. That is a false economy: the wrong cartridge either passes debris or strangles the flow.

What the micron rating does

Micron rating describes the size of particle the cartridge captures. Lower numbers capture finer particles and block sooner.

A 5 micron cartridge in a loop with a marginal pump will block within days and look like a failing chiller.

Pleated, washable or carbon

For a plunge loop, a pleated cartridge of 20–30 micron is the usual compromise between flow and capture.

Fitting the housing

Cartridges are not interchangeable across housings, even when they look similar.

• Check the outside diameter and the end-cap style.
• Confirm the height, including any locating spigot.
• Check the housing O-ring size; a worn ring leaks regardless of the cartridge.
• Confirm the flow rating of the housing, not just the cartridge.

Order one spare before you need it. The week a cartridge clogs is not the week to discover the part number is wrong.

Cleaning that does not wreck the cartridge

1. Remove the cartridge and empty the housing.
2. Rinse from the inside out with a hose.
3. Use a soft brush on heavy deposits; never scrub across the pleats.
4. Avoid pressure washers; they tear the media.
5. Soak in a mild detergent if greasy, then rinse thoroughly.
6. Reinstall with a smear of silicone grease on the O-ring, not on the media.

If flow does not recover after a rinse, the cartridge is done.

When to replace rather than rinse

• Pleats stay discoloured after cleaning.
• Flow does not return to normal.
• The cartridge smells after cleaning.
• The media is torn, collapsed or deformed.
• It has been in service for the full interval the manual states.

Cartridges and sanitation

A filter removes particles; it does not disinfect. A loaded cartridge is a good place for biofilm to grow, which is why the schedule matters more than the rating.

• Keep a sanitiser residual in the water.
• Rinse weekly in heavy use.
• Replace rather than persist with a smelly cartridge.
• Clean the housing interior when you change the cartridge.

Matching cartridge to pump

If you upgrade the cartridge rating, check the pump can still deliver the chiller's flow window with the new restriction.

A finer cartridge:

• captures more,
• blocks faster,
• raises head,
• reduces flow.

That trade is fine if you have headroom and a schedule; it is a trap if the loop was already marginal. The honest test is a week of running: if flow is still strong at the end of it, the rating is sustainable; if it collapses, step back one grade.

Stocking and cost

Cartridges are cheap individually and annoying when missing.

• Keep two spares: one in use, one ready to swap.
• Note the part number inside the housing door.
• Buy the same micron rating unless you are deliberately changing the loop.
• Avoid bulk buys of carbon blocks; they degrade in storage.

The running cost of cartridges is small compared with a fouled heat exchanger or a replacement pump.

Cartridges and water chemistry

A cartridge is not a water treatment system, but it interacts with chemistry.

• Fine cartridges capture flocculated particles after a clarifier.
• Carbon removes some organics and taste, and can remove sanitiser if used incorrectly.
• Heavy scale will not be removed by a cartridge; use a descaler.
• Oily residue from sunscreen loads the media quickly and needs detergent soaking.

If the water smells after filtering, the problem is upstream of the cartridge.

Signs the housing needs attention

• The O-ring is flattened, cracked or missing.
• The housing body is crazed or cloudy.
• The lid threads are stiff or cross-threaded.
• Water weeps from the seal after a change.
• The housing is rated below the pump's pressure.

Housings are cheap. A leaking housing near a chiller's electrics is not.

Frequently asked questions

What micron filter should a cold plunge use?

20 to 30 micron is a practical middle for most plunge loops. Use a coarser cartridge if the pump is marginal, or a finer one only with flow headroom and frequent changes.

Can I wash and reuse chiller cartridges?

Pleated cartridges can be rinsed several times before replacement. Washable mesh lasts longer but filters coarser particles. Carbon blocks are not reusable.

How often should I change a chiller cartridge?

Follow the manual, and replace when flow stops recovering after cleaning. Home plunge loops often need a change every month or two.

Does a finer cartridge make the water cleaner?

It captures smaller particles, but only if flow continues. A finer cartridge that blocks weekly can leave the water worse than a coarser one that keeps circulating.

Can I run the chiller without a cartridge?

No. Without filtration, debris reaches the heat exchanger and flow drops. If you are waiting for a replacement, stop the loop rather than running it unfiltered.