These two companies build a large share of every water heater sold in the United States, plus most of the ones wearing other names. If you are standing in a store deciding between them, the honest answer is that you are choosing between two competent tanks, and the decision that matters more is which line you buy within either brand.
That is not a cop-out. It has a testable basis, and it also has three real exceptions where one brand is clearly the better buy. Both are below.
The short answer
- Replacing a tank this weekend at a big box store: buy whichever brand the closer store stocks, in the longest warranty tier you can afford. Rheem is the Home Depot brand, A.O. Smith is the Lowe’s brand. The warranty tier changes the appliance more than the badge does.
- Buying a heat pump water heater: Rheem. The ProTerra line has held the efficiency lead on the ENERGY STAR listings and it offers a 120 volt plug-in version that fits houses with no spare panel capacity.
- Buying tankless: Rheem. It has been building its own tankless units for years and the parts bench is deep. A.O. Smith’s tankless range is thinner.
- Having a plumber install it: buy whatever the local supply house carries. A brand whose parts are on the van beats a brand your contractor has to order.
- Hard water, over about 10 grains per gallon: neither brand saves you. Buy the 12 year tier of either, which is where the better anode protection lives.
Who owns what
Half the confusion in this category comes from badge engineering. Rheem also sells water heaters as Ruud, Richmond and Eemax. A.O. Smith also sells them as State, American and Reliance, and owns Lochinvar on the commercial side. Two people comparing four brands are often comparing two factories.
Both are American manufacturers with American plants. Rheem has built water heaters in Montgomery, Alabama for decades. A.O. Smith’s plant in Ashland City, Tennessee is one of the largest water heater factories in the world. Neither company is the offshore importer the other’s fans on forums like to imply.
Side by side
| criteria | RheemRuud, Richmond, Eemax | A.O. SmithState, American, Reliance |
|---|---|---|
| Where you buy it | Home DepotPlus plumbing wholesalers for the Professional lines | Lowe’sPlus wholesalers for ProLine |
| Retail line | Performance / Plus / PlatinumWarranty tier goes 6, 9, 12 years | Signature / Select / 900Same 6, 9, 12 ladder |
| Trade line | Professional Classic to PrestigeBetter parts, dealer-backed | ProLine, ProLine XESame idea, same gap vs retailtie |
| Heat pump flagship | ProTerra, UEF up to ~4.0120V plug-in version availableefficiency lead | Voltex / Signature 900, UEF ~3.4–3.9Strong, one step behind on paper |
| Tankless | Full range, own manufactureCondensing and non-condensingdeeper bench | Limited rangeNot the reason to pick this brand |
| 50 gal electric, retail | $550–$800By warranty tier | $550–$800Effectively the same shelftie |
| Warranty structure | 6 / 9 / 12 year tankLabor typically 1 year | 6 / 9 / 12 year tankLabor typically 1 yeartie |
| Published failure data | NoneNo public model-level database | NoneSame |
Standard storage tank? Coin flip, decided by which store is closer and which warranty tier is on sale. Heat pump or tankless? Rheem, on published efficiency and on range. Contractor install? Whichever one your plumber stocks, every time.
Why the brands matter less than the tier
Inside either brand, a 6 year tank and a 12 year tank of the same capacity look identical from the outside. What changes is anode protection, sometimes element quality, sometimes insulation thickness. The 12 year unit costs perhaps $150 more and it is the closest thing to a free upgrade in this category, because the thing that kills a tank is corrosion and the anode is what fights it.
The other gap that is larger than the brand gap is retail versus trade. Rheem Professional and A.O. Smith ProLine units are not the same product as the ones on the store shelf, even at matching warranty lengths. They use different components, and they come with a dealer who has a stake in the warranty claim. If a plumber tells you the wholesale unit is better, they are usually right, and they also make more money on it. Both things are true at once.
What nobody can tell you
There is no public database of water heater failures by model. Manufacturers hold their warranty claim rates and no independent body publishes model-level reliability for this category. Every “Brand X lasts longer” claim you will read, including the ones from plumbers with thirty years of experience, is a sample of a few hundred units in one water district.
Those samples are not worthless. They are just local. A plumber in a hard water county in Arizona genuinely does see tanks fail at seven years, and it has almost nothing to do with the badge. Water chemistry, set temperature and whether anyone ever touched the anode explain more variance than the manufacturer does.
What can be verified is on paper: the AHRI directory lists certified efficiency by model number, the ENERGY STAR product finder lists qualifying heat pump units with their UEF, and the warranty document states exactly what is covered and for how long. Those three sources settle most arguments in this category, and they are the only ones we use.
The heat pump exception, in numbers
This is where the choice stops being a coin flip. Both companies make good heat pump water heaters, but Rheem’s ProTerra has generally sat at the top of the ENERGY STAR efficiency table, and it offers a 120 volt plug-in model that runs on an ordinary outlet.
On a household using 64 gallons of hot water a day, at $0.17 per kWh, the difference between a UEF of 4.0 and a UEF of 3.5 is roughly $25 a year. Over twelve years that is $300, which is real but rarely decisive. The 120 volt option is worth far more than the efficiency gap, because it can remove the need for electrical work entirely in a house whose panel is full.
Either way, a heat pump unit is the biggest running cost decision available on an all-electric house. It cuts water heating energy by roughly two thirds against a resistance tank, which dwarfs everything on this page. The full comparison is in tank vs tankless, where all five appliance types are costed over ten years.
How to actually decide, in order
- Fix the type and the capacity first. Tank or tankless, gas or electric or heat pump, and what first-hour rating your morning needs. Our sizing guide has the worksheet. A right-sized Rheem and a right-sized A.O. Smith both work. An undersized anything does not.
- Pick the warranty tier. Twelve years if you are staying, six if you are selling within a few years.
- Then pick the badge. Availability, price on the day, and whether your installer will stand behind it.
I keep meeting people who spent three evenings researching brands and ten minutes on capacity. It is backwards. The badge decision is worth a few hundred dollars over a decade. The sizing decision is worth every cold shower you will take in it.
Sources
- AHRI Directory of Certified Product Performance for model-level efficiency ratings.
- ENERGY STAR certified water heater product finder for heat pump UEF values and qualifying models.
- Manufacturer warranty documents and specification sheets, which are the only place the tier differences are written down.
- Retail pricing observed at national US retailers. Prices move; the ranking between the two brands has not.
We do not accept payment from manufacturers and we do not publish installation quotes. How we build these comparisons, and what we deliberately leave out, is on the method page.