As the technology behind building systems continues to improve, homeowners are fine-tuning their choice of mechanical components. Where inefficient and oversized equipment once lumbered away in concrete-block basements, new streamlined units with better performance over longer life spans now purr as they provide constant comfort.

Attaching hoses to these flush kit valves lets users pump in descaling solution through the cold-water side and out through the hot-water side. The materials needed to flush the system can often be purchased as a kit, including a bucket, hoses, submersible pump, and descaling solution. Photo credit: Matt Risinger

Tankless water heaters are a prime example. As an increasingly popular choice for propane-powered homes, tankless units take up far less space and heat water only when it’s needed, using fuel more economically than tank-style units. Although performance improves dramatically with tankless, so does the required maintenance.

“Most tank-style water heaters have something like a compact car engine,” says Matt Risinger, CEO and chief builder of Risinger & Co. in Austin, Texas. “A 200,000 Btu tankless [water heater] is like a Ferrari engine.” And like upgrading from a small Honda to an Italian sports car, maintenance needs are going to increase along with performance. “A tankless water heater is heating the water on-demand and has to do it quickly because it’s not storing any water,” Risinger explains. “As a result, scale can build up a lot faster, so a tankless water heater will need to be flushed more often than a tank-style unit.”

David Federico, brand director for Rinnai America, agrees. “Maintenance for a tankless water heater is minimal,” he says, “but as with any appliance, if not properly maintained, it can affect the product’s long-term performance and life cycle.”

Flushing the system

The primary maintenance requirement for tankless water heaters is a system flush. This involves pumping a vinegar solution through the unit to break down scale buildup. While many plumbing companies can perform the service for a fee, manufacturers also offer instructions and materials guidelines for homeowners to do it themselves.

“These days, almost all tankless units have flush kits installed,” Risinger says. “It looks like two garden hose hookups, and it allows you to move the vinegar through the unit in a loop.” Risinger has produced a few YouTube videos explaining the process. He estimates that DIY tankless water heater descaling calls for a one-time $100 investment in a submersible pump, descaling solution or vinegar, hoses, and a bucket, which are often sold as a kit. After that, homeowners will have to buy only the descaling solution as needed.

How often to flush

Newer tankless water heaters typically have flush kits attached during installation, making DIY flushing an easier job. An older tankless unit without a flush kit will require a professional to perform the maintenance. Photo credit: Matt Risinger

Unlike tank-style units that could go several years between maintenance, tankless water heaters should be flushed once a year. “The frequency is typically annual, unless the water quality is poor, in which case it’s recommended more frequently,” Federico says. He adds that many units, including those from Rinnai, can be outfitted with modules to remind users when maintenance is due. Some units can even be remotely monitored by the homeowner’s plumbing company. For his family of six, Risinger says he flushes his tankless unit every 12 months — whether the maintenance notifications call for it or not.

Water softening helps

Another factor in Risinger’s frequent tankless water heater flushes is that his family lives in a hard water area. Because scale is caused by a buildup of minerals (mostly calcium), hard water will result in more scale than softer water. Both Risinger and Federico note that adding a water softener can be beneficial for homes with tankless water heaters.

“Water softeners can be very helpful, particularly in areas where the water quality is not optimal,” Federico says. “They can help to increase the life of the product and decrease the frequency of the unit needing to be flushed.”

Not flushing is hazardous

Calcium particles caused by scale buildup in tankless water heaters can clog faucet aerators like this one or get trapped in screens behind shower valves. The result can be costly behind-the-walls repairs, but it is preventable with regular water heater maintenance. Photo credit: Matt Risinger

While most of a home’s mechanical systems are fairly hands-off, Risinger cautions against lax tankless water heater maintenance. Left too long without flushing, excessive scale buildup can cause sand-like calcium particles to start traveling through the water lines. The particles will collect behind aerators and valve screens throughout the home’s plumbing, which can be costly and inconvenient to repair or replace.

“Tankless water heaters are very cleanable, but if you go too long between cleanings, it will start to affect other systems in the house,” he says. “A lot of people never do any maintenance until there’s a problem, so if [your customers are] thinking about installing a tankless water heater, make sure [they are] willing to maintain it.”

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Lauren Hunter