Anodes and Hot Water System Types
All gas, electric and solar mains-pressure water heaters with a vitreous enamel or bonded ceramic coating utilize a sacrificial anode to provide additional corrosion protection.
The common brands are Rheem, Vulcan and Dux as well as Solahart solar heaters.
Less common brands are AQUAMAX electric models, Beasley, Zip, and Quantum.
Which heaters do NOT have an anode?
1. Gravity Fed Tanks located in the ceiling.
These are mostly found in older homes and they are rarely supplied new nowadays due to the fact that the hot water supply relies on gravity alone and as such, it is not very satisfactory for showering.
2. All types of Continuous (Tankless) Gas Heaters.
These are small, wall-mounted heaters which heat the water as it passes through them. Common brands are RINNAI Infinity, RHEEM Integrity, DUX Endurance as well as BOSCH, PYROX, ZIP, etc.
3. Stainless Steel and Copper Storage Type Heaters.
These heaters look similar to the ones that do require an anode. They are generally the same size and shape but the tank is either stainless steel or copper and does not require an anode.
Brand names with a stainless steel tank are AQUAMAX gas heaters and EDWARDS, as well as some models of BEASLEY, in both electric and solar types. Copper tanks haven't been produced for many years, but there are no doubt some still surviving because they have been known to last for 40 years or more. They don't ever have anodes in them.
What about older heaters?
The older a heater is, the greater the likelihood of it having little or no remaining active anode and at the same time, having experienced an appreciable deterioration of the "glass" lining, thus leaving areas of exposed steel wall where corrosion may have already started. While that corrosion cannot be reversed, it can certainly be arrested by the introduction of a new anode, which can get to work by reversing the electrical flow and converting the tank wall back to a cathode (parts of it will have become anodic after the original anode ceased operating).