iSpring WGB32B Replacement Filters: Which Cartridges Fit, and Cross-Fit Alternatives

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Short answer

The iSpring WGB32B takes three 20 x 4.5 in cartridges. The iSpring WCB/WGB manual’s stage table puts the FP25B polypropylene sediment cartridge in stage 1 at the inlet and the FC25B carbon block in stages 2 and 3; the set is sold as F3WGB32B, and the housings are iSpring’s HB28B Big Blue. iSpring’s system page rates stage 1 at 5 microns. The FP25B and FC25B product pages each rate the cartridge at up to 100,000 gallons or 12 months at up to 15 GPM, and the manual says to replace every 6 to 12 months, or sooner when pressure is slowing. Pentair’s spec sheets put the Pentek DGD-5005-20 (5 micron) and DGD-2501-20 (1 micron) sediment cartridges at 4.50 x 20 in and the EP-20BB carbon block at 4.63 x 20 in, sized for Big Blue housings. The one spec that must match is the 20 x 4.5 in nominal size; micron rating, capacity and pressure drop change with each cartridge.

The spec people get wrong is not the size but the micron: a 1 micron cartridge fits the WGB32B perfectly and is the wrong buy if your complaint is pressure.

What fits

The iSpring WCB/WGB manual (version 2020-03, repeated in the 05/2021 revision) fixes the stage order: FP25B at the inlet, FC25B in the two positions after it. iSpring publishes a micron rating only for stage 1.

Part	Fits stage	Size	Rating (manufacturer’s published figures)	Link
iSpring FP25B	Stage 1 (inlet), sediment	20 x 4.5 in	5 micron polypropylene; up to 100,000 gallons or 12 months; up to 15 GPM	iSpring FP25B, 1-pack
iSpring FC25B	Stages 2 and 3, carbon block	20 x 4.5 in	Coconut shell carbon block; up to 99% chlorine; up to 100,000 gallons or 12 months; up to 15 GPM; no micron rating published	iSpring FC25B, 1-pack
iSpring F3WGB32B	All three (one FP25B, two FC25B)	20 x 4.5 in	The replacement pack the manual names for the WGB32B	Not linked: no listing for the pack was opened

The housing’s working window does not change with the cartridge: the manual sets it at 25 to 80 psi, 40 to 100 F (4 to 37 C) and 3 to 15 GPM, with 1 in NPT ports on the bracket.

Cross-fit alternatives

The only fit spec either maker publishes is 20 in by 4.5 in nominal. Pentair’s DGD sheet (310061 Rev E) lists both DGD cartridges at 4.50 x 20 in and sized for Pentek Big Blue housings; its EP sheet (310077 Rev E) lists the EP-20BB at 4.63 x 20 in. Neither sheet nor the iSpring pages state end-cap style or inner diameter, so this page does not either. No Culligan cartridge in this size was found.

Alternative	Same size?	Rating (source)	What differs from the iSpring part
Pentek DGD-5005-20 (part 155358-43)	4.50 x 20 in, yes	5 micron nominal; under 1 psi at 20 gpm; 40 to 145 F; 100% polypropylene (Pentair sheet 310061)	Replaces the FP25B. Pentair publishes no gallon capacity; its listing copy says about every 6 months or sooner on a pressure drop. Pressure-drop figure is Pentair’s internal test. NSF/ANSI 42 for material requirements only
Pentek DGD-2501-20 (part 155360-43)	4.50 x 20 in, yes	1 micron nominal; under 1 psi at 20 gpm; 40 to 145 F (Pentair sheet 310061)	Finer than the FP25B’s 5 micron. NDSU Extension: a 2 to 5 micron filter already needs more pressure to push water through, and 1 micron is finer still
Pentek EP-20BB (part 155583-43)	4.63 x 20 in, sized for Big Blue housings	5 micron nominal (85% removal basis); 2.0 psi at 4.0 gpm; over 44,000 gallons at 4.0 gpm on 2 ppm free chlorine with over 90% reduction; 40 to 180 F (Pentair sheet 310077)	Replaces the FC25B. Carries a published chlorine capacity and pressure drop, both from Pentair’s internal testing; the FC25B publishes neither. NSF/ANSI 42 for material requirements only
Aquaboon 5 micron 20 x 4.5, 2-pack	4.5 x 4.5 x 20 in, per listing	5 micron; 100% melt-blown polypropylene; service life up to 4 to 6 months (listing copy)	No manufacturer spec sheet or product page could be found, and the listing names no NSF standard. Every figure in this row is listing copy
Waterdrop WD-WF20PG, 3-cartridge set	4.5 x 4.5 x 20 in, yes	97.72% chlorine reduction; 15 GPM; 12 months; NSF/ANSI 372 (Waterdrop page)	A full three-stage set (sediment, GAC with KDF, carbon), not a lone sediment cartridge. No per-stage micron rating is published, and NSF/ANSI 372 is a lead-free materials standard, not a contaminant-reduction one

NSF’s own standards sheet defines NSF/ANSI 42 as the aesthetic-effects standard (chlorine, taste and odor, particulate) for point-of-use and point-of-entry systems, and NSF/ANSI 53 as the health-effects standard for claims such as lead and VOCs. Pentair’s sheets certify the DGD and EP-20BB to NSF/ANSI 42 for material requirements only; iSpring’s pages say only that its cartridges were tested by an independent third party to meet NSF/ANSI standards, with no number. Neither is a contaminant-reduction listing you can look up.

The chlorine number a carbon stage works against is EPA’s maximum residual disinfectant level, 4.0 mg/L for chlorine and 4.0 mg/L for chloramines. Pentair’s over 44,000 gallon figure for the EP-20BB assumes 2 ppm; a higher residual spends the block sooner. No carbon block above publishes a chloramine claim.

Replacement interval

iSpring’s manual gives 6 to 12 months, depending on the contaminants in the supply, and names the trigger: the system has been working properly and the pressure is slowing. The product pages restate it as up to 100,000 gallons or 12 months per cartridge at up to 15 GPM; the gallons decide whether you reach the 12 months.

Nebraska Extension puts household use at 60 to 80 gallons per person per day: multiply by your headcount and divide 100,000 by the result to see which limit arrives first. NDSU Extension’s rule for activated carbon filters is more conservative, every 3 to 6 months or sooner on decreased flow. The Pentek DGD sheet publishes no capacity or interval; its listing copy says about every 6 months.

After the change, the manual says to run the nearest cold faucet for about 10 minutes to expel carbon fines, never a hot faucet.

Which set to buy

The iSpring set is the one the manual names, and its only certification line is “tested by an independent third-party to meet NSF/ANSI standards”, with no standard number. The Pentek cartridges print NSF/ANSI 42 and a pressure drop, but the certification covers material requirements only and the DGD sheet gives no gallon capacity. For the manual’s exact parts, fit one FP25B and two FC25B . For a published pressure drop and chlorine capacity, fit a DGD-5005-20 and two EP-20BB . Skip all of them if your well water runs orange: none is an iron cartridge, and the iron in well water guide carries those limits. Skip the 1 micron DGD-2501-20 if pressure drop is the complaint, and if your utility disinfects with chloramine, no cartridge here publishes a claim for it.

Frequently asked questions

Which filter goes in which stage of the iSpring WGB32B?

The iSpring WCB/WGB manual's stage table puts the FP25B polypropylene sediment cartridge in stage 1 at the inlet and the FC25B carbon block in stages 2 and 3. The manual sells the three together as replacement pack F3WGB32B, and names the housing as the HB28B Big Blue. iSpring's system page rates stage 1 at 5 microns; no micron figure is published for the FC25B.

How often should the WGB32B filters be replaced?

iSpring's manual says every 6 to 12 months depending on the contaminants in the supply, or when the pressure is slowing on a system that has been working properly. The FP25B and FC25B pages rate each cartridge at up to 100,000 gallons or 12 months at up to 15 GPM. NDSU Extension's rule for activated carbon filters is more conservative: every 3 to 6 months, or sooner on decreased flow.

Do Pentek Big Blue cartridges fit the iSpring WGB32B housings?

Pentair's DGD spec sheet lists the DGD-5005-20 (part 155358-43, 5 micron) and DGD-2501-20 (part 155360-43, 1 micron) at 4.50 x 20 in and says the series is sized for Pentek Big Blue housings. The EP-20BB carbon block (part 155583-43) is 4.63 x 20 in on Pentair's EP sheet. The WGB32B housings take 20 x 4.5 in nominal cartridges, which is the only fit spec either maker publishes.

Does NSF/ANSI 42 on the box mean the cartridge is certified to reduce chlorine?

Not by itself. NSF's standards sheet says NSF/ANSI 42 covers aesthetic effects (chlorine, taste and odor, particulate) for point-of-use and point-of-entry systems, but Pentair's sheets state the DGD and EP-20BB are certified to NSF/ANSI 42 for material requirements only. iSpring's pages say only that its cartridges were tested by an independent third party to meet NSF/ANSI standards, with no standard number given.

What do I do right after changing the WGB32B cartridges?

iSpring's manual says to open the nearest cold water faucet and run it for about 10 minutes to expel carbon fines from the new FC25B blocks, and not to use a hot water faucet for that first flush. The same manual sets the housing's working window at 25 to 80 psi and 40 to 100 F, which stays the same whichever 20 x 4.5 in cartridge you fit.