HonestHomeCost
Water Heaters

Rheem or A.O. Smith: what actually differs?

By Honest Home Cost Editorial Team ·Updated ·4 min read

Short answer

Rheem and A.O. Smith are the two groups behind most water heaters sold in the United States, and the practical difference for an owner is which badges each one stands behind and how each one codes a date. Rheem builds for Ruud, Richmond, GE, Hotpoint and Lowe's own brand. A.O. Smith builds for State, American, Reliance, U.S. Craftmaster, Whirlpool and Kenmore, having bought GSW and American Water Heater Company by 2006. Their serial numbers run in opposite orders, which is the single most common source of a wrong age.

month, then year
How a Rheem serial reads (InspectApedia, Fast Water Heater)
year, then week
How an A.O. Smith serial reads (InspectApedia, Fast Water Heater)
by 2006
When A.O. Smith had bought GSW and American Water Heater (InspectApedia)
over seven years
The age error from reading one brand by the other's rule

What we will not do on this page

Most pages answering this question declare a winner. We are not going to, because we have no evidence that would support it. We have not tested these units, we do not have failure-rate data, and the warranty documents that would let us compare coverage term by term are not published in a form we could read, as we set out in our age decoder work.

What we do have is the ownership structure, the serial formats and the badge lists, all from sources you can check. Those answer a more useful question than "which is better": what am I actually looking at, and what does it mean for me.

Who owns which badge

Group Badges it builds for
Rheem Ruud, Richmond, GE, Hotpoint, Lowe's own brand
A.O. Smith State, American Water Heater, Reliance, U.S. Craftmaster, Whirlpool, Kenmore

Both lists are from InspectApedia's brand index and Fast Water Heater, which agree on the groupings. The A.O. Smith list is longer than it looks: InspectApedia's State page names more than twenty further badges State Industries produced, among them Ace, Century, Crosley, Nationaline, Sears and Thermo-king.

The corporate route to that list is documented. InspectApedia on A.O. Smith: founded in 1915, first US patent in 1936 for the glass-lined tank, and "by 2006 the company had purchased both Canadian GSW Incorporated and the American Water Heater Company." Their American page gives the other end of the same chain: American Water Heater Company was "founded around 1972, was merged into GSW in 2002 and in turn GSW later merged into AO Smith."

What this means in practice, marked as our reading: a Whirlpool, a Kenmore and a State tank can come out of the same plants. If you are comparing two quotes on different badges from this group, you may be comparing the same heater twice.

The difference that costs people money

The two groups code dates in opposite orders. This is not a quality difference, it is a trap.

Plate reads 1219 Group Reading Result
on a Rheem badge Rheem month 12, year 19 December 2019
on an A.O. Smith badge A.O. Smith year 12, week 19 May 2012

Over seven years from the same four digits. Fast Water Heater calls it "the single most common mix-up we see, because the same four digits mean completely different things depending on the brand."

We got this wrong ourselves on Kenmore and corrected it on 8 October 2026, which is documented on the Kenmore page.

The per-brand detail sits on its own pages: Rheem, A.O. Smith, State, American, Whirlpool, GE and Kenmore.

One documented difference in the hardware

InspectApedia notes, in the context of replacement anode rods, that a flexible magnesium anode sold as a fit for "AO Smith, Rheem, Reliance, Richmond, Kenmore, GE & State water heaters" is not compatible with Bradford White units.

Read for what it says rather than what it does not: on this specific part, Rheem and A.O. Smith units are interchangeable with each other, and a third group is not. That is a point in favour of either of these two over a more unusual badge when it comes to sourcing parts years from now. See the anode rod page for what the part does and costs.

What we would compare instead

Our advice, marked as ours. Since neither group can be ranked from public evidence, compare the two quotes in front of you on things that are written down:

  • The warranty term on the specific model, not the brand. Terms vary more within a brand than between brands, and the number on the box is checkable.
  • The installer. Our installation labor page covers what that part costs, and a good install outlasts a brand preference.
  • Parts availability for your model, which the anode note above speaks to.
  • Whether a tank or tankless unit suits the house, a decision that matters far more than the badge on it.

None of our sources frames the comparison this way. It is our conclusion from what they do document.

Sources

  1. InspectApedia, Water Heater Age and Manuals (brand index showing which badge belongs to which group)
  2. InspectApedia, A.O. Smith Water Heater Age (company history, acquisitions, serial formats)
  3. InspectApedia, American and American Standard Water Heater Age (the 1972, GSW 2002, A.O. Smith corporate chain)
  4. Fast Water Heater Company, How Old Is My Water Heater? (both family rules and the mix-up they cause)

Price figures are national US ranges from the sources above as of the date shown. Your local price depends on labor rates, permits and site conditions. Read how we get our numbers.