20 Inch Big Blue Cartridge Compatibility: Which 20 x 4.5 in Filters Fit Any Housing
Every 20 in Big Blue housing takes a 20 x 4.5 in cartridge: Pentek DGD at 4.50 in, EP-20BB at 4.63 in, 1 to 25 micron. Carbon block runs fatter than sediment media.
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Short answer
Any 20 in Big Blue housing takes a 20 x 4.5 in nominal cartridge. Pentair’s DGD Series sheet (310061 Rev E) states the line is sized for Pentek Big Blue filter housings and lists the DGD-5005-20 and DGD-2501-20 sediment cartridges at 4.50 x 20 in (114 x 508 mm), under 1 psi pressure drop at 20 gpm. Pentair’s EP Series sheet (310077 Rev E) lists the EP-20BB carbon block at 4.63 x 20 in (118 x 508 mm) maximum, 5 micron nominal, with a published capacity over 44,000 gallons at 4.0 gpm and 2 ppm free chlorine. That eighth of an inch is real: carbon block media runs fatter than spun polypropylene and still fits the same sump. Micron ratings on the DGD sheet run 1 to 25, all nominal, not absolute. iSpring’s WGB32B system, built around the same 20 x 4.5 in cartridge and a 1 in NPT port, confirms the sizing independently of Pentair.
What fits
Sediment stage, most housings: the default
Pentek DGD-5005-20
4.50 x 20 in, 5 micron nominal dual-gradient polypropylene; under 1 psi at 20 gpm; NSF/ANSI 42 material
Sediment stage when 5 micron lets fines through
Pentek DGD-2501-20
4.50 x 20 in, 1 micron nominal dual-gradient polypropylene; under 1 psi at 20 gpm; NSF/ANSI 42 material
Carbon stage, city water with a chlorine residual
Pentek EP-20BB
4.63 x 20 in carbon block, 5 micron nominal; 2.0 psi at 4.0 gpm; over 44,000 gallons at 2 ppm free chlorine
The number people match cartridges to is the port size stamped on the housing cap, and it sets the plumbing, not the cartridge that fits inside.
Which cartridges fit a 20 in Big Blue housing?
Every part below is a 20 x 4.5 in nominal cartridge from Pentair’s own DGD and EP spec sheets. A nominal rating is the maker’s stated percentage of particles removed at that size, not an absolute cut-off.
| Cartridge | Type | Micron (nominal) | Pressure drop or capacity (maker’s figure) | Dimensions | Source |
|---|---|---|---|---|---|
| Pentek DGD-5005-20 (155358-43) | Dual-gradient spun polypropylene sediment | 5 | Under 1 psi at 20 gpm | 4.50 x 20 in (114 x 508 mm) | Pentair DGD sheet 310061 Rev E |
| Pentek DGD-2501-20 (155360-43) | Dual-gradient spun polypropylene sediment | 1 | Under 1 psi at 20 gpm | 4.50 x 20 in (114 x 508 mm) | Pentair DGD sheet 310061 Rev E |
| Pentek DGD-7525-20 (155356-43) | Dual-gradient spun polypropylene sediment | 25 | Under 1 psi at 20 gpm | 4.50 x 20 in (114 x 508 mm) | Pentair DGD sheet 310061 Rev E |
| Pentek EP-20BB (155583-43) | Bonded PAC carbon block | 5 | 2.0 psi at 4.0 gpm; over 44,000 gallons at 2 ppm free chlorine | 4.63 x 20 in (118 x 508 mm) maximum | Pentair EP sheet 310077 Rev E |
Note the two dimensions: Pentair’s EP sheet gives the EP-20BB at 4.63 in maximum and its DGD sheet gives the sediment line at 4.50 in, an eighth of an inch narrower, which is why a carbon block sits tighter in a clear sump. Both sheets say their cartridges carry NSF/ANSI 42 certification for material requirements only, not a contaminant-reduction claim.
What else fits the same housing?
Pentair’s DGD sheet documents fit only inside Pentek’s own Big Blue housings. Other makers publish the same nominal 20 x 4.5 in size for their own systems, which is the number that has to match, not a cross-brand fit guarantee.
| System | Port | Cartridge size published | Other published limits | Source |
|---|---|---|---|---|
| iSpring WGB32B | 1 in NPT | 20 x 4.5 in | Up to 15 GPM | iSpring WGB32B product page |
| Express Water WH300SCKS | 1 in, per the Express Water WH300SCKS replacement filters page | 20 x 4.5 in | Not independently confirmed this session | Not independently sourced this session |
Buy the cartridge by the 20 x 4.5 in size and match the port to the existing plumbing. Neither maker here publishes an o-ring or sump-thread spec against the other, so this page does not claim they interchange.
How often do they need replacing?
The DGD sheet publishes no gallon capacity and no interval: a sediment cartridge is finished when the pressure drop across it climbs, and the sheet’s under 1 psi at 20 gpm is the starting point, not a service life. Pentair’s EP sheet gives a capacity at a stated flow: over 44,000 gallons at 4.0 gpm for the EP-20BB, based on 2 ppm free available chlorine and greater than 90 percent reduction. A higher chlorine residual spends the block sooner.
Sediment load ahead of the carbon stage shortens every interval. On well water with visible turbidity, read the best whole house sediment filter for well water page before buying a 1 micron cartridge, and check the whole house filter flow rate calculator for whether the housing’s flow rating covers the house.
Which cartridge to order
The Pentek DGD-5005-20 is 5 micron nominal, not absolute, and Pentair publishes no capacity for it; its case is a published pressure drop and a 4.50 in diameter that fits any housing built for Pentek’s own Big Blue line.
The EP-20BB carries a published 44,000 gallon chlorine figure but runs 4.63 in, so a sump that is tight with a carbon block is behaving as the sheet says.
Skip the 1 micron DGD-2501-20 if the complaint is low pressure, and skip every cartridge here if the water is orange or smells of sulfur: the iron in well water and rotten egg smell guides carry those limits.
Frequently asked questions
Why is the Pentek EP-20BB listed at 4.63 in when other Big Blue cartridges run 4.50 in?
Pentair's EP Series sheet (310077 Rev E) gives the EP-20BB carbon block as 4.63 x 20 in maximum, while its DGD Series sheet (310061 Rev E) lists the DGD-5005-20 and DGD-2501-20 sediment cartridges at 4.50 x 20 in. Carbon block media runs about an eighth of an inch fatter than spun polypropylene and still fits the same Big Blue sump.
Is a 1 micron Pentek DGD-2501-20 the same length as the 5 micron DGD-5005-20?
Yes. Pentair's DGD sheet lists the DGD-2501-20 (1 micron nominal) and the DGD-5005-20 (5 micron nominal) at the same 4.50 x 20 in (114 x 508 mm) dimension, with the same under 1 psi pressure drop at 20 gpm. The micron rating changes filtration, not the cartridge's physical size.
Does the DGD Series fit housings other than Pentek's own Big Blue?
Pentair's DGD sheet states the series is sized for Pentek Big Blue filter housings specifically. iSpring's WGB32B page separately lists 20 x 4.5 in cartridges for its own housing, the same nominal size, though no maker here documents a cross-brand fit guarantee beyond that shared number.
What does NSF/ANSI Standard 42 mean on these cartridges?
Pentair's EP and DGD sheets both state their cartridges are tested and certified to NSF/ANSI Standard 42 for material requirements only, not a contaminant-reduction claim. The EP-20BB's chlorine taste and odor capacity is a separate, internally tested figure, not part of that certification.
How much flow can a 20 in Big Blue system actually handle?
iSpring's WGB32B page states its 20 x 4.5 in system handles up to 15 gpm. Pentair's DGD sheet rates the cartridge itself at under 1 psi pressure drop at 20 gpm, so the housing and the plumbing behind it, not the cartridge, usually set the practical limit for a whole house.
