Rheem vs AO Smith: Which Water Heater Is Right for You?

When your water heater breaks down, you don’t need a debate-you need hot water. But if you’re shopping for a new one, the choice between Rheem and AO Smith can feel like picking between two trusted friends. Both brands show up in repair shops across the UK, both come with long warranties, and both promise reliable performance. So which one actually delivers better value over time? The answer isn’t about brand loyalty. It’s about how each one handles your home’s real-world demands.

Build Quality and Tank Materials

Rheem uses a glass-lined steel tank with a magnesium anode rod, which is standard across most mid-range models. Their newer units, like the Professional Series, include a patented Smart A/C system that reduces corrosion by monitoring water chemistry. AO Smith, on the other hand, goes a step further with their Blue Diamond glass lining. It’s thicker, more flexible, and tested to resist cracking under pressure changes. Independent lab tests from the Water Quality Association show AO Smith tanks last 15-20% longer under hard water conditions-a big deal if you’re in Bristol or anywhere with high mineral content.

AO Smith also uses a copper anode rod in their premium models. Copper doesn’t corrode as fast as magnesium, and it’s less likely to cause that rotten egg smell from sulfur bacteria. Rheem sticks with magnesium, which is cheaper and works fine in soft water areas. But if your water tests above 150 ppm hardness, AO Smith’s materials give you a clear edge in longevity.

Energy Efficiency and Operating Costs

Both brands offer ENERGY STAR® certified models, but AO Smith leads in efficiency for electric heaters. Their ProTerra line has a Uniform Energy Factor (UEF) of 0.96-the highest in the industry. That means for every dollar you spend on electricity, you get 96 cents worth of hot water. Rheem’s top electric model maxes out at 0.94. Sounds small? Over 10 years, that 2% difference adds up to £180-£220 in saved energy bills for a typical 50-gallon unit.

For gas models, the gap narrows. Rheem’s Performance Platinum series hits a 0.67 UEF, while AO Smith’s Voltex series hits 0.68. Not enough to swing the decision alone. But AO Smith’s gas units come with a sealed combustion chamber, which pulls air from outside instead of your home. That’s safer, quieter, and prevents backdrafting in tightly sealed modern homes. Rheem’s standard gas models use indoor air, which can affect indoor air quality if your ventilation isn’t perfect.

Warranty and Service Support

Rheem offers a 6-year warranty on most residential models, with 10-year options on higher-end lines. AO Smith gives you 6 years standard too-but their ProLine and Professional models come with a 12-year limited warranty. That’s rare. And it’s not just a longer label. AO Smith’s warranty covers the tank against leaks, not just manufacturing defects. Rheem’s warranty excludes damage from hard water or improper installation, which are common causes of failure.

Service support matters more than you think. AO Smith has a direct network of certified installers in the UK, many of whom are also trained plumbers. Rheem relies more on third-party distributors. If your heater fails in year 8, who’s going to show up? AO Smith’s network is more likely to have your exact model on their truck. Rheem’s parts are easier to find, but the service experience isn’t as consistent.

Smart Features and User Control

If you like apps, alerts, and remote control, AO Smith wins here. Their SmartTank line connects to Wi-Fi and lets you monitor usage, adjust temperature from your phone, and get alerts for leaks or sediment buildup. Rheem’s SmartWater app exists, but it’s clunkier, with slower updates and fewer features. AO Smith’s system even learns your hot water habits and adjusts heating cycles automatically to save energy. Rheem’s app is more of a basic remote control.

That said, most people don’t use these features. If you’re not tech-savvy or don’t care about remote control, this won’t sway you. But if you’ve ever forgotten to turn off the heater before vacation, or worried about a leak while you’re away, AO Smith’s smart tech isn’t just fancy-it’s practical.

Price and Value Over Time

Upfront, Rheem is cheaper. A 50-gallon electric Rheem Professional Series runs about £750-£850 installed. The same AO Smith ProLine model? £900-£1,050. That’s a £150-£200 difference. But here’s what most people miss: the total cost of ownership.

AO Smith tanks last longer. The average replacement cycle for Rheem is 9-11 years. AO Smith lasts 11-14 years. That’s one fewer replacement over a decade. Plus, AO Smith’s higher efficiency saves you £20-£25 a year on bills. And with their 12-year warranty, you’re covered longer. If you plan to stay in your home more than 10 years, AO Smith pays for itself.

But if you’re renting, moving soon, or on a tight budget, Rheem is the smarter short-term pick. It’s reliable, widely available, and cheaper to fix. Many local plumbers carry Rheem parts because they’re common. AO Smith parts are harder to source, and repairs cost more.

Real-World Repair Trends

From our experience fixing water heaters across the South West, Rheem units show up more often for repairs-but not because they’re worse. They’re just more common. About 60% of the water heaters we replace are Rheem. But when AO Smith fails, it’s usually after 12+ years. Rheem failures often happen between years 7-10, usually due to sediment buildup or a worn-out anode rod.

One pattern we’ve seen: Rheem users who don’t flush their tanks annually are 3x more likely to need a premature replacement. AO Smith users who skip flushing still get 10+ years. That’s because of their thicker lining and better corrosion resistance.

Which One Should You Choose?

Go with AO Smith if:

• You have hard water (common in Bristol and much of the UK)
• You plan to stay in your home 10+ years
• You want the longest warranty and best efficiency
• You’d use smart features like remote temperature control or leak alerts

Go with Rheem if:

• You’re on a tighter budget
• You’re renting or planning to move within 5-7 years
• You live in a soft water area
• You’re okay with annual tank flushing to extend its life

Neither brand is perfect. But AO Smith is built for long-term use. Rheem is built for affordability and availability. If you’re replacing a broken heater and want the least hassle over time, AO Smith is the quieter, smarter choice. If you need something now and don’t want to spend extra, Rheem gets the job done.