Direct answer: North Star’s single-cabinet softeners step up by capacity and flow. The NSC22 (22,100 grains, 0.65 cu. ft. resin) and NSC31 (31,300 grains, 0.81 cu. ft.) share a 3/4-inch valve and a 7.2 gpm rated service flow; North Star lists them for households of 1–4+ and 1–5+ people. The NSC42 (42,100 grains, 1.20 cu. ft.) moves to a 1-inch valve, 9.9 gpm and higher hardness and iron limits. The NSCWC adds activated carbon for chlorine taste and odor to a 35,600-grain softener in the same cabinet size. All four cabinets measure 48 x 15 x 20-1/2 inches.
Publisher boundary: Water System Guide is an independent research publisher, not a North Star dealer. Figures come from manual 7393624 (NSC22 and NSC31) and manual 7393632 (NSC42), both Rev. H dated January 7, 2026, and North Star product pages, reviewed October 15, 2026. We did not review NSCWC, NSCWHC or NST manuals. Household sizes are North Star’s guidance. North Star publishes no prices; see our North Star ownership costs guide.
The cabinet models side by side
| Specification | NSC22 | NSC31 | NSC42 | NSCWC (2-in-1) |
|---|---|---|---|---|
| Part number | NSC2223 | NSC3123 | NSC4223 | NSCWC23 |
| Model code (manual) | n22P | n31P | n42P | Not reviewed |
| Maximum rated capacity | 22,100 grains at 10.4 lbs. | 31,300 grains at 12.9 lbs. | 42,100 grains at 16.3 lbs. | 35,600 grains (product page) |
| Rated efficiency at minimum dose | 4,474 grains/lb. at 1.9 lbs. | 5,090 grains/lb. at 2.4 lbs. | 4,940 grains/lb. at 2.5 lbs. | 4,780 grains/lb. at 2.9 lbs. |
| Resin | 0.65 cu. ft. | 0.81 cu. ft. | 1.20 cu. ft. | 0.98 cu. ft. plus activated carbon |
| Rated service flow | 7.2 gpm | 7.2 gpm | 9.9 gpm | 8.0 gpm |
| Pressure drop at rated flow (manual) | 13.7 psi | 14.9 psi | 11.9 psi | Not reviewed |
| Maximum supply hardness (manual) | 95 gpg | 110 gpg | 120 gpg | Not reviewed |
| Maximum clear-water iron | 6 ppm | 8 ppm | 11 ppm | 3 ppm |
| Valve | 3/4 in., up to 1 in. plumbing | 3/4 in., up to 1 in. plumbing | 1 in., up to 1-1/4 in. plumbing | 3/4 in., up to 1 in. plumbing |
| Household size (product page) | 1–4+ | 1–5+ | 1–6+ | 1–6+ |
| Weight (product page) | 78 lbs. | 86 lbs. | 97 lbs. | 114 lbs. |
Sources: NSC22/NSC31 manual specifications; NSC42 manual specifications; product pages for the NSC22, NSC31, NSC42 and NSCWC.
Shared limits from the manuals: 20–125 psi water pressure, 40–120°F water temperature, a minimum supply flow of 3 gpm and a maximum drain flow of 2.0 gpm. All three cabinet manuals and product pages list NSF/ANSI 44, NSF/ANSI/CAN 372 and CSA B483.1.
Capacity at each salt dose
The manuals rate each softener at three salt doses. The controller picks a dose at each regeneration, so the capacity actually restored varies.
| Dose point | NSC22 | NSC31 | NSC42 |
|---|---|---|---|
| Lowest | 8,700 grains at 1.9 lbs. | 12,300 grains at 2.4 lbs. | 12,400 grains at 2.5 lbs. |
| Middle | 18,500 grains at 6.2 lbs. | 26,200 grains at 7.7 lbs. | 33,300 grains at 9.5 lbs. |
| Highest | 22,100 grains at 10.4 lbs. | 31,300 grains at 12.9 lbs. | 42,100 grains at 16.3 lbs. |
At the lowest dose, the NSC31 and NSC42 restore almost the same capacity. The NSC42’s larger bed pulls ahead at the middle and high doses. Our NSC31 vs NSC42 comparison looks at that pair in more depth.
Where the product pages and manuals differ
A few published figures don’t match between documents. We show both rather than choose:
- NSC31 capacity. The product page’s feature list says “max grain capacity of 31,100,” while its specification table and the manual list 31,300 grains. North Star’s own filter on the softener listing page includes both 31,100 and 31,300 entries.
- Intermittent flow. The manuals rate intermittent flow at a 15 psi pressure drop: 7.6 gpm (NSC22), 7.3 gpm (NSC31) and 11.5 gpm (NSC42). The product pages rate it at a 30 psi drop: 11.3, 14.6 and 17.8 gpm. They are different test conditions, not a correction.
- NSC22 efficiency. The manual lists 4,474 grains per pound; the product page lists 4,475.
- Household size for the NSC42 and NSCWC. Both product pages describe the softener as serving “households of any size,” while each specification table says 1–6+ people. North Star’s listing filter shows both “1-6+” and “Any” entries.
- Rated service flow vs intermittent flow. The manuals note that intermittent flow “does not represent the maximum service flow rate used for determining the softeners’ rated capacity and efficiency.” Running continuously above the rated service flow “may affect capacity and efficiency performance.” Size for the rated service flow, not the intermittent figure.
When an installer quotes a model, the manual’s figures for the dose and flow they plan to use are the ones to hold them to.
NSC22 and NSC31: same cabinet, more resin
The NSC22 and NSC31 share one owner manual, one parts list and a 3/4-inch valve (NSC22/NSC31 manual). Both have a TANK LIGHT button and a low salt light. The NSC31 adds 0.16 cubic feet of resin, raises the hardness limit from 95 to 110 gpg and iron from 6 to 8 ppm, and has the best minimum-dose efficiency of the range. Its pressure drop at rated flow is a little higher, 14.9 psi against 13.7.
The reviewed NSC22/NSC31 manual has no salt-type setting, so it does not document potassium chloride programming.
NSC42: the 1-inch valve model
The NSC42 has its own manual and a 1-inch valve rated for up to 1-1/4-inch plumbing. Its controls differ from the smaller models: a WATER USE button shows current flow and average daily gallons, a tank light switches on when the magnetic salt lid opens, and a salt-type screen sets NaCl or KCl (NSC42 manual, PDF page 17). Error codes display as Err1 to Err5 rather than E1 to E5.
At 9.9 gpm with an 11.9 psi drop, it delivers more flow with less pressure loss than the NSC31. It also uses more water per full-dose regeneration, 45.9 gallons against 31.1.
NSCWC and NSCWHC: softening plus carbon
The NSCWC product page describes a “2-in-1 system [that] softens water and reduces chlorine taste & odor with carbon filtration.” It lists NSF/ANSI 42 for chlorine taste and odor and NSF/ANSI 44 for hardness, barium and radium 226/228. Its iron limit is the lowest in the group at 3 ppm, so it is not the choice for iron-bearing well water. North Star lists the NSCWHC as a 2-in-1 softener and whole-home filtration system with Wi-Fi. We did not review either system’s manual.
Two-tank models
North Star’s softener listing also includes three two-tank models, the NST30ED, NST45ED1 and NST70ED1, named as 30,000-, 45,000- and 70,000-grain softeners. They use different equipment from the cabinet models, and nothing on this page or in the NSC manuals applies to them.
What every cabinet model shares
The four product pages list the same feature set: AutoSense Technology, which North Star says “learns water usage patterns to optimize water use and regeneration frequency”; reverse flow regeneration; a low salt monitor; an inner tank light; suitability for city or well water; and an installation kit with a custom-fit bypass valve. Each lists a 1-inch male pipe thread connection. The warranty line is identical on all four: “1 year on all parts | 5 year on electronics and valves | 10 year on tanks.” Choosing a model therefore comes down to capacity, flow, water limits and carbon, not warranty or features.
How to choose
- Test the water. Hardness above 95 gpg rules out the NSC22, and above 110 gpg the NSC31. Clear-water iron above 3, 6 or 8 ppm rules out the NSCWC, NSC22 or NSC31 respectively. The manuals add that Wisconsin “requires additional treatment if water supply contains clear water iron exceeding 5 ppm,” whatever the softener’s rating.
- Check peak flow and pipe size. Homes with 1-1/4-inch plumbing or high simultaneous use point to the NSC42.
- Decide on chlorine taste and odor. Only the NSCWC and NSCWHC include carbon.
- Plan the space. All four cabinets need 48 inches of height plus room to open the salt lid.
Our softener sizing calculator estimates the daily grain load, and the grain capacity guide explains why capacity at a lower salt dose matters. The North Star brand research records certification listings by model.
Frequently asked questions
What is the difference between the North Star NSC22 and NSC31?
They share a manual, a 3/4-inch valve and a 7.2 gpm service flow. The NSC31 has more resin (0.81 vs 0.65 cubic feet), a higher capacity (31,300 vs 22,100 grains) and higher hardness and iron limits.
Which North Star softener is best for 1-1/4-inch plumbing?
The NSC42, which North Star lists with a 1-inch valve for up to 1-1/4-inch plumbing. The NSC22, NSC31 and NSCWC use a 3/4-inch valve for up to 1-inch plumbing.
Does North Star make a softener with a carbon filter?
Yes. The NSCWC and Wi-Fi NSCWHC combine softening with activated carbon. The NSCWC product page lists NSF/ANSI 42 for chlorine taste and odor reduction.
How big is a North Star NSC31?
The product page lists 48 inches high, 15 inches wide and 20-1/2 inches deep, weighing 86 pounds, the same cabinet dimensions as the NSC22 and NSC42.