How to Winterize a Pool Filter - Sand, DE, and Cartridge
Winterizing your pool filter incorrectly causes freeze damage that voids warranties. This guide covers the correct procedure for sand, DE, and cartridge filters - including drain points, O-ring care, and storage.
Why Winterizing Your Filter Matters
A filter tank that freezes cracks. A multiport valve with standing water splits. DE grids with ice inside them tear.
The repair cost for freeze damage to a pool filter ranges from $150 (valve) to $800 or more (tank replacement). The time cost of winterizing correctly is about an hour. Every year, pool owners skip winterization and pay for it in spring.
What Happens When Water Freezes in Your Filter
Water expands approximately 9% in volume when it freezes. A filter tank holds several gallons of water in the sand, around the laterals, and in the underdrain.
When that water freezes:
- The expanding ice cracks the filter tank (fiberglass or ABS plastic both fail)
- Lateral arms inside the sand filter crack at their connections
- The multiport valve body splits if standing water is trapped in the valve ports
- DE grid fabric tears under the pressure of ice forming inside the grid channels
None of these failures are immediately obvious - they look fine until spring startup, when the cracked filter either leaks immediately or fails within the first run cycle.
Winterizing a Sand Filter - Step by Step
Tools needed: Flathead screwdriver or socket wrench for drain plugs, O-ring lubricant
- Do a final backwash and rinse cycle
- Turn off the pump and circuit breaker
- Remove the drain plug(s) from the filter tank bottom
- Open the air relief valve at the top of the filter
- Allow the tank to drain completely (10-15 minutes)
- Set the multiport valve to WINTERIZE (or position between settings)
- Remove the pressure gauge and store indoors (cold can freeze the Bourdon tube)
- Lubricate all O-rings with silicone lubricant
- Store drain plugs somewhere you will find them in spring (the skimmer basket is a classic spot)
Do not: Leave the valve in any locked position. Do not add fresh sand or any chemicals to the filter before closing.
Winterizing a DE Filter - Step by Step
Tools needed: Filter cleaner, O-ring lubricant, storage space for grids (in hard freeze climates)
- Do a final backwash cycle - do not recharge with DE
- Turn off the pump and circuit breaker
- Release pressure through the air relief valve
- Remove the drain plug from the filter tank
- In mild climates: allow the tank to drain, leave assembled
- In hard freeze climates: disassemble the filter completely, remove the manifold and grids, rinse each grid with a hose, store indoors dry
- Leave the drain plug removed and the air relief valve open
- In spring: reassemble, check grids for damage, add fresh DE charge
Winterizing a Cartridge Filter - Step by Step
- Remove the cartridge from the filter housing
- Clean the cartridge thoroughly with a garden hose (spray between pleats)
- Soak in cartridge filter cleaner overnight if it has been more than one season
- Store the clean cartridge indoors in a bucket of clean water (prevents the media from drying and cracking)
- Drain the filter housing completely
- Leave the drain plug removed
- Store the housing lid loosely in place (not sealed)
Recommended cartridge cleaning products: Pool cartridge filter cleaner on Amazon - use a dedicated cartridge cleaner, not bleach or household cleaners.
O-Ring Maintenance at Closing
Winterization is the best time to inspect and lubricate all O-rings.
O-rings degrade over time - they dry out, crack, and lose their seal. Cold winters accelerate this degradation. Inspecting them at closing means you know the condition before spring startup, not after the pump is already running and leaking.
Check:
- Multiport valve O-ring (large O-ring on the valve base)
- Drain plug O-rings
- Union O-rings in the plumbing
- Filter lid O-ring (cartridge and DE filters)
Apply a thin coat of pool-safe silicone lubricant. Do not use WD-40, vegetable oil, or Vaseline on rubber O-rings - these degrade rubber over time. Pool silicone lubricant is inexpensive and specifically formulated for this use.
Pool O-ring silicone lubricant on Amazon
Spring Startup Checklist
Before reopening in spring:
- Replace drain plugs (with fresh O-rings if the old ones are cracked)
- Reinstall the pressure gauge
- Reinstall the cartridge (cartridge filters) or add fresh DE (DE filters)
- Set multiport valve to FILTER position
- Prime the pump
- Check all connections for leaks before leaving the equipment running unattended
Related Guides
- How to Backwash a Pool Filter - final backwash procedure
- How to Change Pool Filter Sand - spring sand replacement if needed
- How Much DE for Pool Filter - spring recharge quantities
- Pool Filter Maintenance Complete Guide - full maintenance schedule
Frequently Asked Questions
Do I need to drain my pool filter for winter?
Do I need to winterize my pool filter in warm climates?
Can I leave sand in my sand filter over winter?
Should I add antifreeze to my pool filter?
When should I winterize my pool filter?
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