Honestly, finding a water heater that doesn't eat up your entire utility closet or crawl space is a nightmare. Most units are built like giant metal silos. If you're looking at the AO Smith DEL 20, you've probably realized it's one of the few "lowboy" options that actually packs a punch without needing its own zip code.
It’s small.
Specifically, we're talking about a 20-gallon commercial-grade electric tank that stands just over 22 inches tall. But don't let the "compact" label fool you into thinking it's just for tiny apartments or under-sink setups. This thing is a workhorse designed for "recovery," which is industry speak for getting your water back to scalding temperatures as fast as possible after you've used it all up.
Why the AO Smith DEL 20 is actually a "Lowboy" legend
The "DEL" in the name stands for Dura-Power Electric Lowboy. In the world of plumbing, a lowboy is basically a squashed version of a standard heater. While a regular 20-gallon tank might be tall and skinny, the AO Smith DEL 20 is short and wide—about 21-3/4 inches in diameter.
This footprint is intentional.
It’s meant to slide under counters, into cabinets, or into those weirdly cramped basement corners where a standard 4-foot tank just won't fit. What most people get wrong is assuming that because it's short, it's less powerful. Actually, this unit is often kitted out with heavy-duty elements ranging from 1.5 kW all the way up to 6 kW depending on your specific electrical setup.
✨ Don't miss: How to recover deleted pics from phone: What actually works in 2026
The "Blue Diamond" factor
AO Smith is obsessed with their glass lining. They call it Blue Diamond® glass coating. Basically, they fuse a ceramic-like glass to the internal steel tank at incredibly high temperatures. Why should you care? Because water is corrosive. Over time, it eats through steel like acid through paper.
The glass lining acts as a shield. It’s flexible enough to expand and contract as the water heats up and cools down, which prevents the lining from cracking. If that glass stays intact, your tank doesn't rust. If it doesn't rust, you aren't calling a plumber at 3:00 AM because your basement is a swimming pool.
Technical specs that actually matter
If you're looking at the spec sheet, your eyes might glaze over at the talk of "unbalanced three-phase delta" or "bonderized undercoats." Let's simplify that.
- Height: 22-1/4 inches.
- Diameter: 21-3/4 inches.
- Capacity: Exactly 20 US gallons (about 76 liters).
- Weight: It’s roughly 73 to 78 pounds when empty. Once it’s full of water? You’re looking at over 240 pounds. Do not try to move this alone.
- Voltage: It’s versatile. You can find these in 120V, 208V, 240V, or 277V.
One thing that surprises people is the terminal block. AO Smith builds these with a factory-installed terminal block that makes the wiring straightforward. You basically just bring the power to the heater and hook it up. However, it's worth noting that the 120V and 277V models usually don't come with this block—you'll be wiring those into a junction box instead.
What it’s like to live with the DEL 20
I’ve seen these installed in small hair salons, doctor's offices, and even in tiny homes. In a commercial setting, it’s great because it provides a steady stream of hot water for hand-washing or light cleaning. In a residential setting, 20 gallons is... tight.
If you take a 15-minute shower with a standard showerhead, you’ve basically used the whole tank.
That’s where the "recovery rate" comes in. If you have the 6 kW version, it can heat about 68 gallons of water per hour (at a 36°F rise). That means even though the tank is small, it’s "recovering" hot water fast enough that the next person can shower sooner than they could with a cheap, low-wattage alternative.
Common complaints and real-world issues
No product is perfect. Looking at user feedback and technician reports, the most common gripe isn't about the tank itself, but the anode rod.
The anode rod is a "sacrificial" piece of metal inside the tank. It’s designed to corrode so the tank doesn't. In areas with "hard" water (lots of minerals), these rods can react and cause a "rotten egg" smell. AO Smith uses an anode rod with a stainless steel core to make it last longer, but you still need to check it. If you ignore it for three years, don't be shocked if the heater starts acting up.
📖 Related: Why is c.ai down today? What Really Happened
Another thing: the T&P Relief Valve.
It’s located on the top. Sometimes these can drip if your home’s water pressure is too high. It’s not necessarily a defect in the AO Smith DEL 20; it’s the valve doing its job so the tank doesn't explode. But if you see water pooling around the base, check that valve first.
Maintenance: Don't just "set it and forget it"
If you want this thing to last ten years instead of three, you have to do the "anniversary flush."
Every year, turn off the power, hook a garden hose to the drain valve at the bottom, and let it run for a few minutes. This flushes out the sediment—the "sand" and minerals that settle at the bottom. If sediment builds up, it covers the heating element. The element then has to work twice as hard to heat the water through a layer of crud, which eventually causes the element to burn out.
Actionable steps for your installation
Before you click "buy" or hire a contractor, check these three things:
📖 Related: What Is The Phone Number For AT\&T: What Most People Get Wrong
- Check your Breaker: A 6 kW element requires a much beefier circuit than a 1.5 kW element. Make sure your electrical panel can actually handle the load.
- Measure Twice: The DEL 20 is wide. Just because it's short doesn't mean it fits everywhere. Ensure you have at least a few inches of clearance around the diameter for the pipes and the T&P valve discharge.
- Thermal Expansion: If you have a "closed" plumbing system (common in newer homes with a backflow preventer), you must install a thermal expansion tank. Without it, the pressure buildup every time the water heats up will eventually crack the glass lining or the tank itself.
- Permits: In many regions, replacing a water heater requires a permit and a post-install inspection. It seems like a hassle, but it's cheaper than your insurance company denying a claim because of an "unauthorized" installation.
The AO Smith DEL 20 is a specific tool for a specific job. It’s for the person who needs reliable, fast-recovering hot water but doesn't have the luxury of space. If you maintain the anode rod and flush the sediment, it’s easily one of the most durable compact heaters on the market.