s the company who wrote the book on HVAC water treatment (literally wrote the book: Water Treatment for HVAC Water Systems) we have a unique perspective on how to best manage corrosion in boilers and hot water heaters.
Several times per year, our clients from across the US will ask us about the use of sacrificial anode bars in their boilers or hot water heaters. Many times, our clients are told that they can “save money” by discontinuing corrosion inhibiting water treatment in favor of adding a sacrificial anode. While this may sound appealing on the surface, we strongly suggest finding the facts before making a decision like this.
A sacrificial anode is a bar that can be inserted inside the vessel of a steel boiler or hot water heater. The anode is made up of metal(s) that are less noble than steel (i.e. zinc, aluminum, or magnesium). Because they are less noble, the anode “attracts” and disrupts general corrosion by diverting the natural flow of electrons and “sacrifices” itself in the process. The anode will corrode first, while the steel vessel will not. Installing a sacrificial anode bar is typically slightly less expensive than the cost of an annual water treatment service.
Sounds like an easy decision, right? Not so fast.
Sacrificial anodes are a primitive way of “controlling” corrosion in your expensive capital equipment. You are actually not controlling it at all, but rather, this action is may actually be encouraging corrosion. The speed at which the anode bar deteriorates is determined by a vast range of environmental inputs; pH, temperature, hardness, alkalinity, heating demand, just to name a few. Once the anode bar has corroded away, it is rendered completely useless. The corrosion causing agents then begin to attack your boiler or hot water heater. The anodes are hidden inside your vessel; you have no way of knowing when they are spent, or past their effective life. Without a corrosion inhibiting chemical treatment plan, you are leaving the entire steel structure vulnerable to uncontrolled corrosion. This is a risk you should not take. Corrosion will attack the boiler tubes, tube sheet, and vessel, causing catastrophic damage. If the damage is repairable, it will be very costly. If it is not repairable, you will be replacing your entire system.
Potentially more important, the anode bar only addresses general or galvanic corrosion. There are several other types of corrosion that can attack your boiler or hot water heater. Based on our nearly 100 years of experience, oxygen pitting is the single most damaging type of corrosion in a steel firetube boiler. The use of an anode bar does nothing to control or prevent oxygen pitting.
In addition to having no way to know when the anode bar is spent, you also have no way to see if the anode bar has been covered with scale. In many circumstances, water in your boiler or hot water heater can have a high tendency to form scale. Scale typically comes from hard water when minerals build up on the inside of your boiler. When scale builds up on your anode rod, it will become useless because the corrosion causing agents cannot come in contact to the less noble metals. Those corrosion causing agents will then attack any exposed metal in your boiler.
If you are considering using an anode bar, you already know that corrosion happens inside of your boiler or hot water heater. When water, heat and metal interact, corrosion happens. The risks associated with a sacrificial anode greatly outweigh the small annual cost savings. Here are a few questions to ask yourself:
- How big of an anode bar do I need?
- How long will that anode bar last?
- Is oxygen pitting a problem in my boiler?
- Do I have a scale formation problem in my boiler?
- What is the volume and quality of my condensate return?
- Is it worth risking the integrity of my large piece of capital equipment to save a very small amount of money?
If you cannot answer any of those questions, or you do not like your answer to any of those questions, we highly recommend using a tried and trusted chemical water treatment program.
Sacrificial anode bars may be useful in small, singly family home domestic hot water heaters; in which chemical treatment is unlikely, and the cost to replace the unit is very inexpensive. But if you have a large boiler or hot water heater, in a multi-family building, or in a commercial/industrial setting, a chemical corrosion inhibitor is absolutely necessary.
After nearly 100 years in business, we would never recommend our clients leave the metal in their boilers or hot water heaters exposed and unprotected. The sacrificial anode bar is a gimmick. It will work. But you have no idea when it will stop working. And when it stops working, your boiler is completely unprotected.
If you must install a anode bar, do so in conjunction with a chemical treatment program with monthly service to give you the piece of mind that the “un-seeable” inside of your boiler or hot water heater is always properly protected.
For more information visit our website at https://metrogroupinc.com/water-treatment/