Gas water heaters aren’t exempt from anode rods based on the heat source. If the gas unit has a tank, then an anode rod is needed. The exception is a gas water heater with a stainless steel tank; this is corrosion resistant and doesn’t need the anode. Tankless gas water heaters also don’t need anode rods.
I’ve been doing research on anode rods recently (anything to avoid actually replacing it). In my procrastination, I discovered that some water heaters don’t need an anode rod! Now, I inherited a relatively new gas water heater when I moved into my house, and this is the first time I was going to replace the anode rod. As I have only ever had electric water heaters in the past, I was very much hoping that my current unit was one of the exceptions. Alas, it is not, but yours might still be.
This quick guide will help you to understand which water heaters have anode rods and when and why they’re necessary.
Heat Source Irrelevant to Anode Rod Necessity
First, let’s briefly cover what an anode rod is. An anode rod is a cylindrical piece of metal that sits inside a water heater’s tank. It is designed to protect the tank from corrosion by attracting damaging minerals and compounds in the water.
This is why anode rods are often referred to as “sacrificial.” They “sacrifice,” or wear themselves out to help your tank last longer, and are much smaller, cheaper, and easier to replace than the tank is.
Because of what an anode rod is designed to do, the need for one is dependent on whether or not your heater has a tank and what that tank is made of. It is not related to whether the heat source is gas, electric, or even solar.
This is why we will mainly be focusing on if your water heater has a tank and what kind of tank it is.
Tank-Style Gas Water Heaters
Glass-Lined: Needs Anode Rod
If you were asked to think of a water heater, a conventional tank-style heater would probably come to mind first. A glass-lined tank is the most common type.
Without getting into the nitty-gritty, tank-style water heaters work by making and maintaining the temperature of large quantities of hot water. Glass-lined water heaters have a layer of glass inside the tank to protect the metal from corrosion and rust.
Unfortunately, it’s almost impossible to ensure that there aren’t any microscopic defects in this glass layer. Additionally, mineral deposits build up against the lining of the tank over time and crack it. These cracks and defects allow water to seep through the glass and corrode the metal of the tank itself.
This is why anode rods are considered necessary in glass-lined tanks. By attracting the corrosive elements that are in the water to themselves, they dramatically delay damage to the tank.
Of course, technically, it’s possible to have a glass water tank without an anode rod, but this will significantly decrease the amount of time your tank can last without replacement.
Stainless Steel: No Rod Needed
While the purpose of an anode rod is to extend the life of the tank by drawing harmful elements towards itself, a tank-style water heater made from stainless steel does not need an anode rod. This is because the material of the tank itself is already resistant to corrosion.
Stainless steel is produced with at least 10.5% chromium, an element that reacts with the surrounding oxygen to create a thin oxide barrier on the tank’s waterside. This oxide barrier protects the other materials used to produce the steel by keeping the water from touching and interacting with them.
Thanks to their natural protection against corrosion, the tanks of stainless steel water heaters generally have a longer service life than glass-lined water heaters. However, this is balanced out by the fact that they’re also more expensive.
Tankless Gas Water Heaters: No Anode Rod
As the name suggests, tankless water heaters don’t have holding tanks for hot water. Instead, they rapidly heat water as it is needed.
This absence of a holding tank means there are no anode rods in tankless heaters, as the purpose of the rod is to extend the tank’s lifespan.
Instead of maintaining large quantities of hot water, tankless heating systems work by running water through a pipe called a “heat exchanger.” A tankless gas water heater uses gas burners placed below the heat exchanger to get it to the high temperatures required for producing hot water in an instant.
For example, it’s important to keep in mind that while the absence of a tank means there’s no place for an anode rod, this does not mean that a tankless heater doesn’t run the risk of corrosion. It is still a metal fixture that is regularly exposed to water and should be checked yearly by a professional to catch damage before it becomes a problem.