What size filter pump do I need for my cold plunge?

Your pump should cycle your entire tub volume in 1 hour or less. For a 50-gallon tub, that's 50 GPH minimum. The Intex C1500 (1500 GPH, $89) is the standard choice and handles tubs up to 100 gallons. If your chiller has a built-in circulation pump, your filter pump only needs to handle filtration (lower flow is fine). If your chiller doesn't have a pump, your filter pump handles both circulation and filtration.

How often should I run my cold plunge filter pump?

4-8 hours per day, ideally on the same timer as your chiller (overnight is common for lower electricity rates). The filter catches skin cells, hair, and debris that feed bacteria. Running it less than 4 hours/day leads to cloudy water within 1-2 weeks. Running it continuously uses more electricity without much benefit.

How often should I replace my cold plunge filter cartridge?

Every 2-4 weeks depending on usage. Hose off the cartridge weekly (takes 2 minutes) to extend its life. Replace it monthly for daily plungers, every 6-8 weeks for occasional use. Signs it needs replacement: water flow drops noticeably, cartridge looks brown even after hosing, or water becomes cloudy. Intex Type A/K cartridges cost about $5 each on Amazon.

Can I use a sand filter for my cold plunge?

Yes - sand filters are more expensive upfront ($200-300) but eliminate cartridge replacements. Sand lasts 3-5 years before needing replacement. Sand filters also handle larger debris better and provide finer filtration. The trade-off: they're larger, heavier, and require backwashing (a 5-minute process every 2-4 weeks). For most DIYers, the Intex C1500 cartridge filter ($89) is sufficient - sand filters are overkill for residential plunge use.

Cold Plunge Filters and Pumps Setup Guide

Why your filter pump matters

Your filter pump is the unsung hero of your cold plunge. It moves water through your chiller (without flow, your chiller can't cool), through your filter (without filtration, your water grows biofilm in 2 weeks), and through your ozone injector (without flow, ozone can't sanitize). A failed pump means no cooling, no filtration, no sanitation — a useless plunge.

This guide covers filter pump sizing, installation, and maintenance.

Sizing your filter pump

Filter pump flow rate is measured in gallons per hour (GPH). The rule of thumb for cold plunge: your pump should be able to cycle your entire tub volume in 1 hour or less. For a 50-gallon tub, that's 50 GPH minimum — but most pumps are rated much higher.

Tub size	Minimum pump GPH	Recommended pump
25 gal	500 GPH	Intex C1500 (1500 GPH)
50 gal	1000 GPH	Intex C1500 (1500 GPH)
100 gal	1500 GPH	Intex C1500 (1500 GPH) or larger
150+ gal	2000+ GPH	Intex 2500 GPH or pool-grade pump

Most chillers have a built-in circulation pump — if yours does, you only need a separate filter pump if you want additional filtration beyond what the chiller provides. If your chiller doesn't have a built-in pump, your filter pump serves both purposes (circulation + filtration).

The Intex C1500: the DIY standard

The Intex C1500 Cartridge Filter Pump is the most popular choice for DIY cold plunges, and for good reason:

1500 GPH flow rate — handles tubs up to 100 gallons
$89 price — cheapest quality option
Standard cartridge filter — replacement cartridges are $5 each, available everywhere
Quiet operation (40-50 dB) — suitable for indoor installations
Simple installation — barbed fittings, no glue required
1-year warranty — typical for the price point

The trade-off: the C1500 uses small paper cartridges that need replacement every 2-4 weeks (depending on usage). For larger tubs or heavier use, consider upgrading to a sand filter pump — more expensive upfront but no cartridge replacements.

Installation

Step 1: Choose a mounting location

Mount the filter pump at or below the waterline of your tub, on a stable surface. Most DIYers mount it on a small shelf or platform next to the chiller. Ensure the pump is level — tilted mounting causes premature bearing wear.

Step 2: Plumb the suction line

Connect the pump's suction (inlet) port to a bulkhead fitting near the bottom of your tub. Use 3/4" flexible PVC spa hose — never garden hose, which collapses under suction. Add a check valve on the suction line if your pump is mounted above the waterline (prevents backflow when pump stops).

Step 3: Plumb the return line

Connect the pump's return (outlet) port to either: (a) a return bulkhead near the top of your tub (if running filter only), or (b) the inlet of your chiller (if your chiller doesn't have a built-in pump). In either case, use flexible PVC spa hose.

Step 4: Install the filter cartridge

The Intex C1500 uses a Type A/K cartridge (about $5 each on Amazon). Insert the cartridge into the pump housing, secure the housing with the twist-lock cover. Run the pump for 1 minute to verify flow — you should see water moving through the clear housing.

Step 5: Wire to a timer

Plug the pump into a mechanical or smart timer (both $10-15 on Amazon). Set to run 4-8 hours per day — most DIYers run it on the same timer as their chiller, typically overnight when electricity rates are lower.

Maintenance schedule

Task	Frequency	Time
Inspect cartridge	Weekly	1 min
Hose off cartridge	Weekly	2 min
Replace cartridge	Every 2-4 weeks	2 min
Inspect pump housing for cracks	Monthly	1 min
Lubricate O-rings (silicone grease)	Every 3 months	5 min
Deep clean pump housing	Every 6 months (at drain time)	15 min

Troubleshooting common issues

Issue: Pump runs but no flow

Air lock — disconnect the suction line briefly to release trapped air
Clogged cartridge — replace or clean
Blocked suction bulkhead — clear debris from inside the tub
Kinked suction hose — straighten

Issue: Pump hums but doesn't start

Frozen impeller (winter) — bring pump indoors to thaw
Debris lodged in impeller — disassemble and clean
Failed capacitor — pump needs replacement

Issue: Pump leaks at housing

Loose twist-lock cover — hand-tighten
Worn O-ring — replace (parts available on Amazon)
Cracked housing — replace pump

Issue: Pump is loud

Cavitation (air in suction line) — bleed air
Worn bearings — pump nearing end of life
Loose mounting — tighten hardware
Debris in impeller — disassemble and clean

💡 Pro tip: dual-filter setup

For plunges used by multiple people daily, consider a dual-filter setup: a coarse pre-filter (mesh screen, $10) before the pump catches hair and large debris, extending the life of your fine cartridge filter. The pre-filter is cleanable and reusable — just hose it off weekly. Your fine cartridges will last 2-3x longer between replacements.

📚 Related

For the full water care protocol, see our water care guide. For plumbing instructions, see our master build guide.