Quick Answer: Both owner's manuals name the same manufacturer, Water Channel Partners in Minnesota, and the warranties are nearly identical. The Rheem RHS42 (Preferred Plus) has the better numbers on paper: 9.9 gpm of flow, 140 gpg max hardness and 42,400 grains. But Rheem says it sells its softeners only through The Home Depot, so it isn't on Amazon. The Whirlpool WHES40E is the more widely sold of the two, but it's currently out of stock on Amazon too. If you're shopping there, the EcoPure EP42 is the closest in-stock match: 42,000 grains, up to 11 ppm of clear-water iron and the same warranty structure. Pick the Rheem if you need the extra flow for three or more bathrooms. Smaller homes can step down to the EcoPure EPS110, and anyone who wants Wi-Fi alerts should look at the GE Smart 35,000 Grain.
Disclosure: As an Amazon Associate, Grains & Gallons earns from qualifying purchases.
Pull up the Rheem RHS42 owner's manual and check the last page: "Water Channel Partners, Eagan, MN." Pull up the Whirlpool manual for its 40,000-grain softener: "Water Channel Partners, Woodbury, MN." Same company, two addresses in the same metro, two logos.
That changes the question. You're not comparing a water-heater company against an appliance company. You're comparing two trims of the same family, sold through different stores, with a few spec differences that matter for some homes and not at all for others.
In this guide
The figures side by side
From the Rheem RHS42 manual and Whirlpool's manual for the WHES40 (the Whirlpool 40,000-grain model; the Amazon listing is the WHES40E):
| Rheem RHS42 (Preferred Plus) | Whirlpool WHES40 / WHES40E | |
|---|---|---|
| Capacity by salt dose | 12,400 @ 2.5 lb · 29,900 @ 8.0 lb · 42,400 @ 16.3 lb | 17,300 @ 3.4 lb · 31,600 @ 9.0 lb · 40,000 @ 15.5 lb |
| Max hardness | 140 gpg | 125 gpg |
| Max clear-water iron | 11 ppm | 10 ppm |
| Rated service flow | 9.9 gpm @ 12.0 psi drop | 7.6 gpm @ 14.7 psi drop |
| Rated efficiency | 5,010 grains/lb at min. dose | 5,094 grains/lb at min. dose |
| Regen water, min. dose | 2.5 gal per 1,000 grains | 3.0 gal per 1,000 grains |
| Resin | 1.20 cu ft | 1.14 cu ft |
| Certifications | NSF/ANSI 44 (incl. barium, radium 226/228), NSF/ANSI 372, WQA to CSA B483.1 | NSF/ANSI 44, NSF/ANSI/CAN 372, WQA to CSA B483.1 |
| Warranty | 1 yr full (5 yr with Rheem cleaner) · 3 yr control board · 10 yr tanks | 1 yr full (5 yr with Whirlpool cleaner) · 3 yr control board · 10 yr tanks |
| Where sold | The Home Depot only (per Rheem) | Many retailers (currently out of stock on Amazon) |
One flag on the Whirlpool flow figure: a retailer listing for the WHES40 shows 8.5 gpm, while the manual says 7.6. We used the manual. Either way, the Rheem is higher.
Three differences that matter
1. Flow. 9.9 gpm against 7.6 is the biggest real-world gap. In a 1- or 2-bath house you'll never feel it. With three bathrooms, or a big rain head plus laundry running, the Rheem keeps more pressure when demand peaks. Its pressure drop at rated flow is also lower (12.0 psi vs 14.7).
2. Very hard or iron-heavy water. The Rheem is rated to 140 gpg and 11 ppm of clear-water iron. The Whirlpool is rated to 125 gpg and 10 ppm. Few homes are anywhere near 125 gpg, but if your well report shows 8+ ppm of iron, extra headroom is welcome. Read our guide on whether a softener can remove iron before you rely on either one for it. A softener handles clear-water (ferrous) iron, not the orange flakes you see once iron oxidizes.
3. Where you can buy and return it. Rheem says its Preferred series is sold exclusively at The Home Depot. If you want to order on Amazon, or your nearest Home Depot doesn't stock the size you need, that decides it, though right now the Whirlpool 40k is out of stock on Amazon as well.
Three differences that don't
Salt efficiency. 5,010 vs 5,094 grains per pound at the lowest setting is a wash. Rheem advertises "about 40% less salt than traditional softeners," but its own site says that's from internal lab testing. Read it as "less salt than an old timer-based unit," not "less than the Whirlpool."
"Smart" learning. Rheem calls it Learning Technology. Whirlpool's retail listing calls it 6th Sense. Both are demand-initiated regeneration with a variable salt dose, which their manuals describe almost word for word. Both also include an optional salt-efficiency mode (off by default, on by law in California) that runs at 4,000 grains per pound or better and regenerates more often.
Warranty. The structures match: one year full, three years on the board, ten on the tanks, extendable to five years of parts-and-labor coverage if you use the brand's softener cleaner every four months. It's the same deal with a different bottle on the shelf. If you go that route, our page on resin and iron cleaners explains what those products actually do.
Rheem's lineup, briefly
The RHS42 is the Preferred Plus model. Rheem's Preferred series also includes:
- Preferred Platinum: Wi-Fi through the iQua app, with salt alerts and remote water management (shutoff valve sold separately)
- Preferred: essential features for medium households
- Preferred Compact: space-saving, no low-salt monitor
All of them come with a double-lined mineral tank and the same warranty structure. If you want the Wi-Fi model, the Platinum is Rheem's answer to GE's smart softener.
The capacity math, using the Rheem's lowest setting
The Rheem's lowest salt setting is very efficient but only removes 12,400 grains. For a couple at 10 gpg (2 × 75 × 10 = 1,500 grains a day), that's eight days per cycle at the most efficient dose. That's excellent salt use, and a good argument for setting your hardness correctly instead of guessing. Our walkthrough on how to set hardness on a softener covers how to compensate for iron too.
A family of five at 20 gpg needs 7,500 grains a day. At the middle dose (29,900 Rheem, 31,600 Whirlpool), either unit regenerates about every four days. That works, but if you're seeing hard water return a day before regeneration, you're undersized. We explain the signs in why hardness returns before regeneration. A household like that should look at Whirlpool's 44k model or a larger Fleck-valve unit instead.
Setup details buried in the manuals
A few lines in these manuals are worth reading before install day, especially on a well:
- Minimum supply flow. Rheem's manual calls for at least 3 gpm of supply flow, because backwash needs it. A small well pump or a long run of 1/2-inch pipe can fall short, so test with a bucket and a timer at the nearest spigot.
- Pressure and temperature. Whirlpool lists 20–125 psi and 40–120°F. Neither unit belongs in an unheated garage that freezes.
- Drain flow. Whirlpool lists a max drain flow of 2.0 gpm, so your drain has to keep up with that during backwash without backing up.
- Salt type. Both manuals allow potassium chloride as an alternative to sodium chloride. Rheem's has a setting to tell the controller which one you're using.
- Extra cleaning. Rheem adds an optional "Clean" feature that extends backwash and fast rinse (1 to 15 minutes), and lets you cap the days between recharges at up to 15. That's handy if your water has some iron, since the resin gets flushed on a schedule even when you're using little water.
None of these will decide Rheem vs Whirlpool on their own. But the minimum-flow note is why some well owners end up with a softener that never fully backwashes.
Picking an alternative on Amazon
If you've decided you want this kind of cabinet softener but neither the Rheem nor the Whirlpool is an option:
- EcoPure EP42: the closest match on paper. It's rated for 42,000 grains and up to 11 ppm of clear-water iron, uses demand-based AutoSense regeneration, and is NSF certified. The warranty is the same shape as the other two: one year full, three on electronics, ten on the tank, extendable to five years of full coverage if you use EcoPure's cleaner regularly. EcoPure markets it for 1–5+ person homes on city or well water. Check price on Amazon.
- EcoPure EPS110: a compact cabinet sized for 1–2 people and 1–2 bathrooms, with the resin tank inside the brine tank. EcoPure says it performs like a 32,000-grain demand unit while using up to 40% less salt. Buying a 40k class unit for a couple usually means sitting at a low salt setting anyway. Check price on Amazon.
- GE Smart 35,000 Grain: adds Wi-Fi flow alerts, low-salt reminders and vacation mode through the SmartHQ app, plus a bypass blending valve so you can dial in how soft the water is. GE says it suits households of up to 6 people and uses 1-inch connections. GE's listing doesn't give a flow or iron rating, so check the spec sheet before you count on it for very hard or iron-heavy wells. Check price on Amazon.
Matching the model to your house
- Rheem RHS42: three or more bathrooms, hardness over 100 gpg, iron near 10 ppm, and a Home Depot nearby.
- Whirlpool WHES40E or EcoPure EP42: almost everyone else in the 2- to 4-person range. The EP42 is the one you can order on Amazon right now.
- Neither: you need more than about 6,000 grains a day of capacity at a moderate salt setting. Size up instead of over-salting a 40k unit.