Our verdict: Worth paying for
Hot tub filters
Short answer
Hot tub filter area runs from 15 to 325 square feet across the 227 spec sheets that list it, with a median of 50. More square footage means slower flow through each foot of filter, so it catches more and clogs later.
Worth paying for
Look for generous filter area; it's a cheap route to clear water. Sundance's 880 has 130 square feet, but its inner core costs $46.99 every 6 months. Hot Spring warns a clogged filter can trip its pump and freeze the tub in winter.
How does a hot tub filter work?
A hot tub filter is a pleated cartridge, usually polyester, sitting in a housing behind the skimmer or under a weir. The pump pulls water through the pleats, which trap hair, skin flakes, lint and the oily film people leave behind, then the clean water heads to the heater and back to the seats. Cartridges are the most common spa filter by far, and larger tubs often pair one with an ozonator.
Area matters because of speed. Spread the same flow over more pleats and the water moves through each square foot more slowly, so finer particles get caught instead of pushed through, and the cartridge takes longer to clog. A trade rule of thumb is no more than 0.375 gallons a minute per square foot of cartridge. By that rule, a pump moving 20 gallons a minute through the filter wants at least 54 square feet.
How many square feet of filter does a hot tub need?
More is better, and the spread is wide. The smallest figure we found is 15 square feet on the Cal Spas Aloha PZ-614L; the largest is 325 on the Hot Spring Aria, which spreads it across several cartridges. Sundance lists 130 square feet on its 880 Series. Some makers stack stages instead of adding area: Jacuzzi runs a pre-filter bag or basket ahead of its cartridges and adds a polishing cartridge on its top models. Generous area is one of the cheapest routes to clear water, so ask for the total square footage and compare it across the tubs you are considering.
How often do you replace a hot tub filter?
Follow the maker's schedule and count it as a running cost. CDC's hot tub guidance calls for replacing cartridges as the manufacturer directs and scrubbing to remove biofilm, and its model code notes that fouled cartridges can shelter bacteria. Some fine inner cores are not rinsable: Sundance's 880 manual says to replace its MicroClean inner core every 6 months, and one parts seller lists it at $46.99. A clogged filter can do more than cloud the water. Hot Spring's 2026 manual warns that dirty filters can trip the circulation pump's cut-off, which risks a freeze in winter if nobody notices. Some cores also carry minerals; see hot tub mineral systems. Owners: see how to clean a hot tub filter, when to replace one and filter size by model.
What to ask the dealer
- How many square feet of filter does it have in total?
- What do replacement cartridges cost, and how often will I buy them?
- Will a cheaper aftermarket filter void my warranty?
The details
Which brands offer it, the research behind the verdict, and the sources.
Which brands offer it
15 brands
| Sundance Spas | 75 to 130 sq ft | 130 |
|---|---|---|
| Hot Spring | 25 to 325 sq ft | 100 |
| Cal Spas | 15 to 150 sq ft | 75 |
| Caldera Spas | 25 to 100 sq ft | 65 |
| Jacuzzi | 50 to 120 sq ft | 60 |
| Artesian Spas | 35 to 150 sq ft | 50 |
| Wellis | 50 sq ft | 50 |
| Marquis | 35 to 50 sq ft | 35 |
| Nordic Hot Tubs | 20 to 45 sq ft | 35 |
| PDC Spas | 25 sq ft | 25 |
| American Whirlpool | Not published | — |
| Bullfrog Spas | Not published | — |
| Dimension One Spas | Not published | — |
| Master Spas | Not published | — |
| Vita Spa | Not published | — |
What the research says
7 findings
- Government The CEC report notes cartridge filters are the most common spa filtration, with larger spas typically pairing a cartridge filter with ozone.
- Trade A pool and spa trade publication gives a general cartridge sizing rule of no more than 0.375 GPM per square foot of filter area, and recommends cleaning when pressure rises about 10 psi.
- Government CDC's Legionella guidance for hot tubs calls for regular cartridge replacement per the manufacturer and vigorous scrubbing to remove biofilm.
- Government CDC's model-code rationale warns that fouled or poorly cleaned cartridges can shelter biofilm bacteria.
- Maker Sundance lists 130 square feet of MicroClean Ultra II filter on its 880 Series.
- Trade A parts seller lists Sundance's MicroClean inner core at $46.99 and says it can't be rinsed; Sundance's 880 manual says to replace it every 6 months.
- Maker Hot Spring's 2026 manual says dirty filters can trip the circulation pump's cut-off, risking a freeze if missed.
Common questions
How many square feet of filter should a hot tub have?
The median across 227 spec sheets is 50 square feet, and the range runs from 15 to 325. A trade rule of thumb is no more than 0.375 gallons a minute per square foot.
How often should you replace a hot tub filter?
As often as the maker says, which varies by cartridge. CDC guidance calls for scheduled replacement and scrubbing; some fine inner cores are not rinsable: Sundance's 880 manual says every 6 months.
Does a bigger filter keep hot tub water cleaner?
Generally yes. More area slows the water through each square foot, so the cartridge catches finer particles and takes longer to clog.
Sources
5
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