A. O. Smith vs Rheem Water Heaters
The two companies that dominate American water heating, compared on published figures rather than reputation.
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A. O. Smith wins on gas delivery and peak heat pump efficiency: a 50-gallon gas unit at 91 gallons first hour, and the Voltex AL at 4.02 UEF. Rheem wins on protection and documentation: integrated leak shutoff limiting a leak to about 20 ounces, a 12-year electric tank warranty, and a published 37 to 145°F heat pump ambient range.
These two companies make most of what you will see. Picking between them is not a quality judgment — it is a question of which specific strength matches your install.
The verdict by category
| Category | Winner | The figure |
|---|---|---|
| Gas tank first-hour rating | A. O. Smith | 91 gal from a 50 gal, 50,000 BTU Signature 100 |
| Heat pump efficiency | A. O. Smith | 4.02 UEF on the Voltex AL against 3.88 on the ProTerra |
| Heat pump first-hour rating | A. O. Smith | 83 gal on the Voltex MAX (66 gal) against 67 gal on the ProTerra (50 gal) |
| Electric tank warranty | Rheem | 12-year tank and parts with 3-year labor on the Gladiator |
| Leak protection | Rheem | Integrated detection with auto shutoff limiting a leak to no more than 20 oz |
| Cold-climate heat pump data | Rheem | Published 37 to 145°F ambient range, Northern Climate Spec Tier 4 |
| Tankless range | Rheem | Prestige RTGH at 5.5 GPM at a 70°F rise; A. O. Smith markets Takagi rather than its own line |
| Anode durability on the premium heat pump | A. O. Smith | Voltex AL anode rated to protect the tank for 10 years |
| Retail availability | Both strong | A. O. Smith at Lowe's, Rheem at Home Depot |
Quick picks
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| # | Product | Best for | Price |
|---|---|---|---|
| 1 | A. O. Smith Signature 100, 50 gal gasThe straightforward 50-gallon gas replacement, and the reason to pay attention to the burner size: the 50,000 BTU version is rated at a 91-gallon first-hour rating against 77 gallons for the 40,000 BTU one. | Most gas tank replacements | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 2 |  Rheem Gladiator 50 gal electricThe electric tank to put above a finished floor: integrated leak detection with an automatic shutoff valve that limits a leak to around 20 ounces, plus a 12-year tank and parts warranty. | Electric tanks in finished spaces | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 3 | A. O. Smith Voltex AL, 66 galThe efficiency leader on this page at 4.02 UEF, in the capacity that suits a five- or six-person household, with a heavy-duty anode rated to protect the tank for 10 years. | Highest published heat pump efficiency | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 4 |  Rheem ProTerra 50 gal hybridThe heat pump water heater to start with: a 3.88 UEF, a 67-gallon first-hour rating, and a 37°F lower operating limit that is the widest ambient range in its class — which is the specification that decides whether it works in a cold garage. | Most heat pump installs | Check price on Amazon No live price feed on this site, so we show none. #ad |
The flagship units side by side
Pick 1 — Most gas tank replacements
A. O. Smith Signature 100, 50 gal gas
The straightforward 50-gallon gas replacement, and the reason to pay attention to the burner size: the 50,000 BTU version is rated at a 91-gallon first-hour rating against 77 gallons for the 40,000 BTU one.
| Capacity | 50 gallons |
|---|---|
| First-hour rating | 91 gallons (50,000 BTU model); 77 gallons (40,000 BTU model) |
| Burner | 50,000 BTU/h ultra-low NOx, or 40,000 BTU/h |
| Dimensions | 61 in H x 22 in dia (50,000 BTU); 60-3/4 in H x 22 in dia (40,000 BTU) |
| Warranty | 6-year tank and parts with 1-year labor (50,000 BTU); 9-year tank and parts with 2-year labor (40,000 BTU) |
What is good
- A 91-gallon first-hour rating from a 50-gallon tank covers back-to-back showers that empty an electric tank of the same size
- Widely stocked at Lowe's, so same-day replacement is realistic when the old one fails
- Ultra-low NOx burner meets the stricter air-district rules in California and Texas
- 22-inch diameter fits most existing alcoves without re-plumbing
What is not
- The longer 9-year warranty is on the smaller burner, so warranty and recovery pull in opposite directions
- Atmospheric venting needs a working chimney or B-vent
- Standing pilot and flue losses mean it idles energy away all day
Skip it if: Skip it if your water heater sits in a sealed closet or a space with combustion air problems. An atmospheric gas tank needs real combustion air and a real flue — the power-vent or direct-vent models exist for exactly that case.
No live price feed on this site, so we show none. #ad
Specifications above from Lowe's listing, Signature 100 50-gal 50,000 BTU; Lowe's listing, Signature 100 50-gal 40,000 BTU 9-year. We have not tested this unit ourselves.
Pick 2 — Electric tanks in finished spaces
Rheem Gladiator 50 gal electric
The electric tank to put above a finished floor: integrated leak detection with an automatic shutoff valve that limits a leak to around 20 ounces, plus a 12-year tank and parts warranty.
| Capacity | 50 gallons |
|---|---|
| Elements | 5,500 W double element, 240 V |
| First-hour rating | 63 gallons |
| Efficiency | 0.92 UEF |
| Leak protection | 360° LeakSense detection with factory-fitted automatic shutoff; leaks limited to no more than 20 oz |
| Warranty | 12-year tank and parts, 3-year labor |
What is good
- The auto-shutoff valve is the single most valuable feature on any tank installed over drywall
- 12-year tank and parts with 3-year labor is among the longest electric warranties sold at retail
- 5,500 W double element gives faster recovery than the usual 4,500 W pair
- Leak alerts arrive before the ceiling does
What is not
- A 63-gallon first-hour rating from 50 gallons is ordinary — electric recovery is slow, full stop
- Running cost is electric-rate running cost; a heat pump model costs far less to run
- The shutoff valve is one more serviceable part in the cold inlet
Skip it if: Skip it if the heater lives on a concrete slab next to a floor drain and you have the headroom for a heat pump model. You are paying for leak protection you can get from a 20-dollar pan, and giving up the running-cost saving a heat pump would deliver.
No live price feed on this site, so we show none. #ad
Specifications above from Home Depot listing, Rheem Gladiator XE50T12CS55U1. We have not tested this unit ourselves.
Pick 3 — Highest published heat pump efficiency
A. O. Smith Voltex AL, 66 gal
The efficiency leader on this page at 4.02 UEF, in the capacity that suits a five- or six-person household, with a heavy-duty anode rated to protect the tank for 10 years.
| Capacity | 66 gallons |
|---|---|
| Efficiency | 4.02 UEF |
| Anode | Heavy-duty, rated to protect the tank for 10 years |
| Warranty | 10-year limited |
| Certification | ENERGY STAR certified |
What is good
- 4.02 UEF is the highest figure of any unit in this registry
- 66 gallons removes the recovery anxiety that a 50-gallon heat pump creates in a big household
- The 10-year anode is a real durability claim, not a marketing one
- ENERGY STAR certification keeps it inside most utility rebate lists
What is not
- 66 gallons is a tall, wide cabinet — measure the space before you order
- Sold mainly through wholesale, so availability is slower than big-box
- Published first-hour rating is not listed for the AL model; the Voltex MAX at the same capacity is rated at 83 gallons
Skip it if: Skip it if your install space is a closet. A 66-gallon heat pump needs air volume to work, and starving a heat pump water heater of air is how you end up running on the backup element and paying resistance rates for a premium appliance.
No live price feed on this site, so we show none. #ad
Specifications above from Auer Steel listing, A. O. Smith HPTS-66 Voltex AL; A. O. Smith Voltex AL introduction. We have not tested this unit ourselves.
Pick 4 — Most heat pump installs
Rheem ProTerra 50 gal hybrid
The heat pump water heater to start with: a 3.88 UEF, a 67-gallon first-hour rating, and a 37°F lower operating limit that is the widest ambient range in its class — which is the specification that decides whether it works in a cold garage.
| Capacity | 50 gallons |
|---|---|
| Efficiency | 3.88 UEF; up to 4.07 UEF advertised on 30 A models |
| First-hour rating | 67 gallons |
| Recovery | 27 gallons per hour |
| Heat pump capacity | 4,200 BTU/h |
| Backup element | 5,000 W |
| Voltage | 208 - 240 V |
| Ambient operating range | 37 - 145°F |
| Cold-climate rating | Meets Northern Climate Specification Tier 4 |
| Leak protection | Integrated detection with factory-fitted auto shutoff; leaks limited to no more than 20 oz |
| Warranty | 10-year limited |
What is good
- A 37°F lower limit means the compressor keeps running in an unheated garage through most of a northern winter
- 3.88 UEF is roughly four times a resistance tank, so the running cost difference is not marginal
- 67-gallon first-hour rating is better than most 50-gallon resistance tanks
- EcoNet control lets you force high-demand mode before guests arrive instead of discovering the limit
What is not
- It is a refrigeration appliance in your house: there is a compressor, a fan and a condensate drain
- Needs roughly 700 cubic feet of air, or louvered doors, in a closet
- It cools and dehumidifies the space it stands in, which is a gift in a Houston garage and a problem in a Minnesota basement
Skip it if: Skip it if the only place it can go is a finished, heated room you occupy. It will steal heat from that room in winter — your furnace then pays for the hot water, and the efficiency you bought disappears.
No live price feed on this site, so we show none. #ad
Specifications above from Rheem ProTerra PROPH50 T2 RH375-30 product page; ABR Wholesalers listing, PROPH50 T2 RH375-30. We have not tested this unit ourselves.
Where A. O. Smith wins
- Gas tank delivery. 91 gallons in the first hour from a 50-gallon unit is the best figure in our registry.
- Peak heat pump efficiency. 4.02 UEF on the Voltex AL.
- Heat pump delivery at capacity. 83 gallons first hour on the 66-gallon Voltex MAX beats an 80-gallon resistance tank.
- Anode rating on the premium line. The Voltex AL's 10-year anode rating against the ProLine XE's 6 — and anode life is what decides when a tank fails.
- Range breadth on retail gas, with multiple burner and warranty combinations.
Where Rheem wins
- Leak protection. The Gladiator and ProTerra both use an automatic shutoff valve that limits a leak to no more than 20 ounces. Nothing in the A. O. Smith range in our registry matches this.
- Electric tank warranty. 12 years tank and parts with 3 years labor.
- Published cold-climate data. Rheem states 37 to 145°F and Northern Climate Specification Tier 4 for the ProTerra. We could not find the equivalent figure for the Voltex line in available documentation, and for a garage install that is the number that matters most.
- A real tankless line of its own, with a rise-qualified 5.5 GPM at a 70°F rise on the Prestige RTGH.
- The 120 V plug-in heat pump, which is the only route to heat pump efficiency where no new 240 V circuit is possible.
Pick A. O. Smith if...
- You are buying a retail gas tank and first-hour rating is the priority.
- You want maximum heat pump efficiency and the install space is warm.
- You need 66 gallons of heat pump capacity with an 83-gallon first-hour rating.
- The 10-year anode rating on the Voltex AL matters to you, which in hard or softened water it should.
Pick Rheem if...
- The tank sits above a finished floor, where the automatic leak shutoff is the most valuable feature available.
- You want the longest electric tank warranty.
- The heat pump is going in a cold garage and you want a published ambient operating limit.
- You need a gas tankless unit, or a 120 V plug-in heat pump.
One thing that is not a tiebreaker
Perceived build quality. Across both manufacturers the tanks are glass-lined steel with a sacrificial anode, and the failure mode is identical: the tank rusts through from the inside. What decides how long yours lasts is the anode rod and your water chemistry, not the badge. How long water heaters last.
What goes in with it
A water heater is a system, not a box. These are the parts that go in with it, and the ones people discover they need halfway through the job.
- Expansion tank
Required by code on a closed system, which is most homes with a pressure-reducing valve.
- Drain pan
Cheap insurance anywhere the tank sits above something you care about.
- Anode rod
The part that decides when the tank leaks. Replacing it is the highest-value hour of maintenance there is.