Direct answer: The Rheem Preferred Plus RHS42 has higher rated service flow and more capacity at its largest published salt dose than the Preferred RHS32. However, its minimum-dose capacity is slightly lower. Choose using measured hardness, treated-water use and simultaneous flow demand. The 32,000- and 42,000-grain product classes do not describe capacity at every regeneration setting.
Publisher boundary: Water System Guide is an independent research publisher, not Rheem water-treatment support or an installer. This comparison uses the RHS32 and RHS42 manufacturer manuals, both Rev. P dated January 20, 2026, checked October 7, 2026. It is a document-based comparison, not a field performance test or a current price quote.
Match the actual model before comparing
The equipment label should say RHS32 for Preferred or RHS42 for Preferred Plus. Their manuals identify Water Channel Partners as manufacturer and warrantor. This comparison does not transfer specifications from Rheem water heaters or from the connected RHW42 Preferred Platinum. The controller code alone is not enough to distinguish RHS42 from RHW42: Rheem’s model-code table assigns rH42 to both, while RHS32 uses rH32.
Our Rheem brand guide gives the broader model context. For a purchase or replacement, put the full equipment model on the proposal and ask for the matching performance sheet.
Rated capacity: keep the salt dose beside the grains
The following pairs come from printed page 4 of the RHS32 manual and RHS42 manual. Each column has its own salt dose. These are not equal-pound tests and are not a menu of homeowner-selected fixed doses: the manuals describe electronic controls selecting a variable dose based on the amount needed.
| Published performance point | Preferred RHS32 | Preferred Plus RHS42 |
|---|---|---|
| Lowest listed dose: grains / salt | 13,000 / 2.6 lb | 12,400 / 2.5 lb |
| Middle listed dose: grains / salt | 27,600 / 8.3 lb | 29,900 / 8.0 lb |
| Highest listed dose: grains / salt | 33,000 / 14.1 lb | 42,400 / 16.3 lb |
| Resin volume | 0.88 cubic feet | 1.20 cubic feet |
| Rated service flow | 7.9 gpm | 9.9 gpm |
| Pressure drop at that rated flow | 14.9 psi | 12.0 psi |
| Intermittent flow at 30 psi pressure drop | 11.8 gpm | 22.4 gpm |
| Total regeneration water at highest listed dose | 33.3 gallons | 45.9 gallons |
Two details change the decision. At the highest listed dose, RHS42 has 9,400 additional grains of rated capacity and uses 2.2 additional pounds of salt per regeneration. At the lowest listed dose, RHS32 has 600 more grains, with 0.1 more pound of salt. A larger product class therefore does not guarantee more capacity at every operating point.
Those figures also do not establish annual salt or water cost. Cycle frequency, changing demand, selected dose and actual operation affect the total. Compare estimates made with the same household inputs rather than multiplying the maximum dose by an assumed weekly schedule.
What the difference means at a known hardness load
Consider a hypothetical home using 300 gallons through the softener daily at 20 grains per gallon hardness, with no iron compensation in this example:
300 gallons/day × 20 grains/gallon = 6,000 grains/day.
Here is the arithmetic if each published capacity point were available for that load:
| Capacity point | RHS32: capacity ÷ 6,000 | RHS42: capacity ÷ 6,000 |
|---|---|---|
| Lowest listed dose | About 2.2 days | About 2.1 days |
| Middle listed dose | About 4.6 days | About 5.0 days |
| Highest listed dose | About 5.5 days | About 7.1 days |
These intervals are illustrations before reserve, variable dosing, iron, household variation and controller rules. They are not regeneration schedules to enter. Their purpose is to show why a headline grain class is inadequate for choosing a model.
Use your own measured hardness and actual treated-water use in our softener sizing calculator. Then ask the seller how the proposed unit will meet that load under its operating settings. A household with guests, an irrigation branch on treated water or a plumbing leak needs its actual use accounted for rather than a people-count assumption alone.
Capacity and peak flow answer different questions
Daily hardness load concerns how much work accumulates between regenerations. Peak flow concerns showers, laundry and other uses happening at once. The RHS42’s rated service flow is 2.0 gpm higher, with the pressure drops shown above at each model’s own rated flow.
The much larger intermittent-flow numbers are measured at a 30 psi pressure drop. They are not substitutes for service-flow ratings. Both manuals explicitly caution that continuous operation above rated service flow can affect capacity and efficiency. A proposal based on RHS42’s 22.4 gpm intermittent figure alone leaves the sustained-flow question unanswered.
Ask the installer to assess the home’s supply pressure and simultaneous fixtures. The published table does not tell us the pressure drop of either model at every possible flow, so it does not establish a complete pressure curve or promise good shower pressure in every installation.
Which model is the stronger candidate?
| Your situation | Decision to check |
|---|---|
| Measured daily load and peak use fit RHS32 | RHS32 remains a candidate; the larger grain label alone is not a reason to replace it |
| More capacity is needed at the higher operating doses | RHS42 has more published capacity in the middle and highest rows; require a demand-based sizing explanation |
| Simultaneous use challenges RHS32’s service-flow rating | Assess RHS42’s higher service flow together with supply pressure and the actual plumbing |
| Hard water appears despite apparently suitable sizing | Check bypass, settings, salt use and recharge behavior before assuming a larger replacement is the answer |
Neither this table nor the laboratory ratings establish the correct treatment for every well. Water chemistry and pretreatment needs still belong in the assessment. A more capable softener is not a substitute for confirming what is in the source water.
Compare the complete installed proposal
Ask each seller to fill in the same short worksheet:
- Full model and dated performance document.
- Raw hardness, units, test date, clear-water iron and relevant water-test results.
- Expected gallons treated daily and simultaneous fixture demand.
- Capacity/dose assumptions, reserve and recharge logic used for the recommendation.
- Supply pressure, installation location, drain arrangement and commissioning scope.
- Equipment, installation and future consumables priced separately, plus the actual warranty and service contact.
Our water softener cost guide helps compare written scopes. Current retailer prices were not verified for this review; request dated equipment and installed quotes.
For an installed RHS32 or RHS42, use the Rheem settings guide to match the controller. If the unit is producing hard water, start with the not-softening checks and record a treated-water test before arranging replacement.
Frequently asked questions
Is the Rheem RHS42 always better than the RHS32?
No. RHS42 has higher rated service flow and more capacity at its middle and highest listed doses, but RHS32 has slightly more capacity at the lowest listed dose. The fit depends on hardness load, peak flow, operating settings and installation.
Does an RHS32 deliver 32,000 grains at every recharge?
No. The reviewed manual lists 13,000 grains at 2.6 pounds of salt, 27,600 at 8.3 pounds and 33,000 at 14.1 pounds. Its electronic controls select a variable salt dose based on need.
Can I use the RHS42 22.4 gpm figure for continuous service?
That is an intermittent-flow figure at 30 psi pressure drop. Its rated service flow is 9.9 gpm. The manual cautions that continuous operation above service flow can affect capacity and efficiency.
Can changing the RHS32 model code turn it into an RHS42?
No. The code must match the installed equipment. Rheem assigns rH32 to RHS32 and rH42 to RHS42; selecting a different code does not change the resin volume or hardware.
Sources and review scope
- Rheem RHS32 manufacturer-authored and manufacturer-hosted owner manual 7386465, Rev. P January 20, 2026; reviewed October 7, 2026.
- Rheem RHS42 manufacturer-authored and manufacturer-hosted owner manual 7386473, Rev. P January 20, 2026; reviewed October 7, 2026.
- Rheem first-party Programming the Model Code, updated February 19, 2026; reviewed October 7, 2026.
The cited manuals and support pages were checked October 7, 2026. This review does not establish current retailer pricing, local inventory, performance in your home or the configuration of a different controller.