Rheem Water Softener Models Compared: Which Preferred Fits?

Direct answer: Rheem sells four softeners. The RHS18 Preferred Compact (18,500 grains, 30-1/4 inches tall) is the small-space model for 1 to 4 people. The RHS32 Preferred (33,000 grains) suits households up to 4 people with up to 1-inch plumbing. The RHS42 Preferred Plus (42,400 grains) adds a 1-inch valve rated for up to 1-1/4-inch plumbing, a higher 9.9 gpm service flow, a built-in sediment filter and a blending valve. The RHW42 Preferred Platinum has the RHS42’s published ratings plus Wi-Fi and the iQua app. Choose by measured hardness, iron, flow and space, not by the grain number alone.

Publisher boundary: Water System Guide is an independent research publisher, not a Rheem retailer. Specifications come from Rheem product pages reviewed October 15, 2026, and, for RHS32 and RHS42, the owner manuals 7386465 and 7386473 (Rev. P, January 20, 2026). We did not review RHS18 or RHW42 manuals. Household-size labels are Rheem’s marketing guidance. We list no prices; see the publisher note in our Rheem running costs guide.

The four models side by side

Sources: RHS18, RHS32, RHS42 and RHW42 product pages. RHS32 and RHS42 figures match their RHS32 and RHS42 manual specification tables.

All four share the same operating limits on their product pages: 20 to 125 psi water pressure, 40 to 120°F water temperature, a minimum supply flow of 3 gpm and a maximum drain flow of 2.0 gpm.

Capacity at every salt dose

A softener’s grain rating depends on how much salt it uses. The manuals list three rated points for the two models we could check fully:

At the lowest dose the two are close; the RHS42’s extra resin shows up at the middle and high doses. The controller picks the dose at each recharge, so the capacity actually used varies. Our RHS32 vs RHS42 comparison goes deeper on those two.

The model name is a class, not a rating. The “18” in RHS18 corresponds to 18,500 grains at the maximum dose, and “32” to 33,000.

RHS18 Preferred Compact: small spaces, low hardness

The RHS18 is the only model under four feet tall. Rheem’s page calls it a “space-saving design” for “condos, townhomes, etc.” and says it uses a sliding lid for salt loading (RHS18 product page).

Its limits are the tightest in the range. Maximum supply hardness is 65 gpg and clear-water iron 3 ppm, against 105 gpg and 8 ppm for the RHS32. Its 0.64 cubic feet of resin and 18,500-grain top rating mean more frequent recharges in a hard-water home. The product page lists model code LE18, a different code family from the rH32 and rH42 of the larger models, so do not assume the RHS32 manual’s menus apply.

RHS32 Preferred: the mid-size model

The RHS32 adds capacity and flow over the RHS18 in a 43-1/2-inch cabinet. Rheem positions it for households up to four people with a high-flow valve for up to 1-inch plumbing (RHS32 product page). Its 7.9 gpm rated service flow comes with a 14.9 psi pressure drop, the highest of the four.

The manual shows the RHS32 uses a 3/4-inch valve with its own parts set, a 9 x 35-inch resin tank and a status light with low-salt and cleaner reminders. It does not have the RHS42’s Clean feature or dedicated salt-level button.

RHS42 Preferred Plus: higher flow and hardness limits

The RHS42 is the step up for larger homes, higher flow or harder water. The product page lists an “ultra high flow valve” for up to 1-1/4-inch plumbing, a built-in sediment filter “with no filter replacements needed,” an illuminated tank light, and an external blending valve for adjusting hardness (RHS42 product page).

The manual confirms several of these as parts and controls: a filter screen (7265025) in the parts list, a 1-inch bypass blending valve (7329594), a dedicated SET SALT LEVEL button, a TANK LIGHT button, and an optional Clean feature that adds a backwash and rinse before recharge for iron or sediment (RHS42 manual, PDF page 13). Its rated service flow is 9.9 gpm at a 12.0 psi drop, so it delivers more flow with less pressure loss than the RHS32.

RHW42 Preferred Platinum: RHS42 ratings plus Wi-Fi

The RHW42’s published ratings match the RHS42’s on every line of the specification table. The differences are connectivity. The product page describes the free iQua app for water-use analytics, salt settings and alerts, continuous-flow alerts and manual regeneration, plus an optional Rheem Preferred Series Water Shut-off Valve for remote shutoff (RHW42 product page). Its low-salt alert shows on the app and the softener display.

The page lists the model code as RH42, the same as the RHS42. Because the code alone does not separate them, use the rating decal inside the salt lid to confirm which you have before ordering parts.

How to choose between them

Rheem’s household-size labels are a starting point. Four measurable checks settle the choice:

1. Hardness and iron. Test the untreated water. If hardness approaches 65 gpg or iron exceeds 3 ppm, the RHS18 is out of range. The RHS32 stops at 105 gpg and 8 ppm; the RHS42 and RHW42 go to 140 gpg and 11 ppm.
2. Peak flow. Count fixtures that run at once. The rated service flows are 7.0, 7.9 and 9.9 gpm, and the manuals note that continuous operation above the service flow rate may affect capacity and efficiency.
3. Pipe size. Homes with 1-1/4-inch plumbing fit the RHS42 or RHW42 by Rheem’s guidance.
4. Space. The RHS18 is about 30 inches tall; the others need 43-1/2 to 48 inches plus room to load salt.

Our softener sizing calculator turns hardness and water use into a daily grain load, and the grain capacity guide explains why the rated capacity at a lower salt dose matters more than the headline number.

What all four share

Rheem’s pages list the same warranty for each model: one year on parts and labor, extendable to five years with Rheem cleaner, three years on electronics and ten years on tanks. All four are sold through The Home Depot, according to the “Buy Exclusively At The Home Depot” links on the Rheem pages. The reviewed RHS32 and RHS42 manuals name Water Channel Partners as manufacturer and warrantor; see our Rheem brand research for certification listings.

Certification on the two documented models

The RHS32 and RHS42 manual covers carry the same certification statement: “tested and certified by NSF International against NSF/ANSI Standard 44 for hardness reduction, efficiency and the reduction of barium and radium 226/228,” certified to NSF/ANSI/CAN Standard 372, and tested and certified by the Water Quality Association against CSA B483.1 (RHS32 manual, PDF page 1). The specification pages list the barium challenge as 10 mg/L reduced to 2.0 mg/L, and radium 226/228 as 25 pCi/L reduced to 5 pCi/L. For the RHS18 and RHW42, confirm the exact model in the certifier’s listing, which appears under the manufacturer’s name.

Frequently asked questions

What is the difference between the Rheem RHS32 and RHS42?

The RHS42 has more resin (1.20 vs 0.88 cubic feet), a higher top rating (42,400 vs 33,000 grains), a higher service flow (9.9 vs 7.9 gpm), higher hardness and iron limits, a 1-inch valve, a sediment filter screen and a Clean feature.

Is the Rheem RHW42 different from the RHS42?

Its published ratings match the RHS42’s. The RHW42 adds Wi-Fi with the iQua app for alerts, usage data and remote regeneration, and works with an optional shut-off valve.

Which Rheem softener is the compact model?

The RHS18 Preferred Compact, at 30-1/4 inches tall. It is rated at 18,500 grains, 65 gpg maximum hardness and 3 ppm maximum clear-water iron.

How many people is a Rheem 32,000-grain softener for?

Rheem’s product page says the RHS32 Preferred serves households of up to 4 people. Measured hardness and water use should confirm the fit.