How hard water can affect a tankless water heater

Most American households have varying degrees of hard water. While hard water is safe for consumption, it can create some minor and major headaches for your plumbing system.

What is hard water?

Before we dive into how hard water can cause problems with your plumbing we should take a high-level look at what hard water is. When runoff water soaks through soil and rock, it dissolves minuscule amounts of minerals. Calcite, and magnesium are the most common form of minerals which cause calcium buildup in water heaters. For a more scientific view of hard water, please click here

If you have noticed a film on your bathtub or shower, you most likely have hard water. Also, hard water limits the sudsing and cleaning capabilities of many detergents and soap.

When hard water is heated, it causes the particles to suspend in the water. They attracted to each other causing them to stick together. When these particles stick together, they become heaver than water and sink.

Hard Water Build Up in Coper Pipe

Gas Water Heaters with a Tank

In a conventional gas-fueled tank water heater, the heating element (the burner) is at the bottom of the storage tank. The water heats up, and the particles sink, and the process repeats itself over and over.  Over time, the lower part of the tank fills up with particles, the particles act as an insulator and cause the burner to be less efficient. In extreme cases, the burner will have to run so long that the steel becomes overheated causing the tank to leak. This can lead to the dreaded “tank rupture” which cause 40-60 gallons of water to flood your basement.

Electric Water heaters with a Tank

Electric tank water heaters are less prone to tank rupture because the heating elements are suspended in the top and middle of the storage reservoir. While most of the calcium will sink to the bottom, some of it will become attached to the heating elements, shortening the lifespan of the water heater.

Tankless Water Heaters

Tankless water heaters are not immune to hard water either. However, the effects on tankless water heaters are minimal and time delayed. As water moves through the heat exchanger, the minerals will drop out of suspension, but most of the minerals will be cleared out with the water flushing through. Thus the build up of scale takes a longer time.

As the scale builds up (more extended period of time) it will cause the heat exchanger to overheat. We believe every current tankless water heater on the market has a safety shut off when a heat exchanger overheats. This prevents damage to the unit and safety to the homeowner. If the unit is reset without the problem being corrected, it will only function for a very short time before the unit shuts itself down.

Most tankless water heaters require a yearly maintenance. The primary purpose of this maintenance is to flush the unit of any scale build up. A vinegar-like solution is run through the unit to clean out any scale build up. The time between cleanings depends on how hard your water is and how much the unit is used. The general guideline is once a year for maintenance.

Some manufacturers such as Rinnai has built in scale detection, which will alert the homeowner on when the unit needs to be flushed. The scale detection for Rinnai is only available on their Ultra and Luxury series.

The best way to prevent hard water is to have your water treated with a water softener. This not only helps your tankless water heater, but it also helps increase the longevity of your plumbing system.

Preventing Hard Water and Extending the life of your Water Heater

The best way to extend the life of your water heater regardless if it’s a conventional water heater or tankless water heater is to install a water softener. A water softener will make you tap water taste better, can extend the life of your water heater and in some cases stop your clothes from getting a yellowish tint them.

How does a water softener work?

A water softener is a mechanical device which is you, or a plumber can install inline with your main water supply. All softeners work with the concept of removing minerals with sodium. Don’t worry about the sodium; it only traces amounts. The chemical process is called ion exchange.

A softener holds a small amount polystyrene beads and salt. The beads have a negative charge. Both calcium and magnesium have a positive charge. When the incoming water passes through the polystyrene beads, the calcium and magnesium cling to the beads. After a few cycles, the beads become saturated with calcium and will no longer attract more calcium. To solve this issue, the unit does a regeneration cycle where the beads are soaked in sodium chloride solution. The soaking causes the calcium to lose it connection with the polystyrene beads, creating a brine. The brine is then flushed through a drainpipe, and the process starts all over.

Almost all residential water softeners use the combination of beads and salt to remove hard water elements. The biggest difference is on how and when the regeneration cycle is activated.

Electronic Timer: A timer causes the cycle to run at set intervals. The unit can not supply soft water when while recharging.

Computerized: Most of these units have a reserve resin, which means you can get soft water while the unit is recharging.

Mechanical Systems: These units have 2 tanks and are much larger. One tank recharges while the other tank makes soft water. These are the most versatile of the units.

How much does a water softner cost?

The cost of a water softener can range from slightly over $100 all the way up to several thousands of dollars.