For many, if not most, commercial applications, hot water is an absolute necessity — critical to keeping the doors open and maintaining business as usual. Hot water at the correct, preset temperature is needed for everything from cleaning dishes in a local café to running washing machines at a laundromat to operating sinks at a neighborhood salon.

After an incredibly tough year dealing with the COVID-19 global pandemic and the subsequent stay-at-home orders and mandated lockdowns across the country, the success of these businesses in 2021 relies heavily on having steady and often large volumes of hot water to meet demands during peak hours of operation. At the same time, each establishment needs far less hot water during slower times of the day. 

Traditional water heaters equipped with an internal storage tank are limited during peak demand times by their storage capacity. During nonpeak hours, they reheat large volumes of hot water that go unused. However, tankless water heaters operate on-demand only to deliver the hot water needed to meet the

How Banking Works

“Banking” refers to installing multiple tankless water heaters that all serve the same hot water system, eventually dumping the water back into a common manifold. This method of providing hot water to fixtures remains the most popular for commercial buildings.

Because of the modularity of tankless water heaters, they are generally not a single heat source but work well as a team. Intelligent controls are programmed to note the amount of hot water needed at a particular moment and which heaters are required to meet that demand. Next, the heaters split the workload and, as a result, only a certain number of units activate to meet demand at that specific time. 

For example, if a building is operating at 30 percent capacity with a three-tankless water heater system, only one would be firing while the other two remain idle. Alternatively, if the building is operating at 100 percent capacity, all three units would fire to meet peak hot water demand. 

With a bank of three tankless heaters, each is piped in parallel. Separate cold water lines enter each unit and separate hot water lines exit each, joining into a common hot water line in the end. 

When banking multiple tankless water heaters in a commercial application, no hot water demand is too large if the system is sized properly. The heaters will communicate with one another to generate enough output to meet demand and “smooth” the load among the various operating units to extend system life. Wi-Fi capability allows the building owner or manager to monitor system operation and be alerted to any problems on their mobile phones.

The typical firing sequence is as follows:

1. The first tankless water heater activates as soon as there is a call for hot water within the system, i.e., someone turns on a faucet or a shower. There also is an option to start two tankless units as default. 

2. This first unit provides all the needed hot water until demand exceeds 80 percent of unit capacity. 

3. Depending on the system, this percentage is customizable. All units allow a quick staging option in which the next heater fires after the first reaches 50 percent of capacity. This is a customizable option to adjust the staging condition. 

4. Once demand surpasses the first unit’s preset capacity, the load is spread between two or more units.

Modulating burner technology can accurately track and meet any hot water demand, matching fuel consumption to current hot water requirements. As noted, if only the BTUs from one water heater are needed, only one will activate. Some banking systems integrate as many as 24 tankless units, controlled by a single remote controller. For even larger applications, multiple systems can be linked together to meet demand. 

The maximum BTU output of the entire system to the minimum BTU output of a single tankless water heater in the system is the turndown ratio. The higher this ratio, the greater the system’s flexibility. 

For example, a bank of 24 tankless water heaters with a minimum-to-maximum BTU range of 15,000 to 7.2 million would have a turndown ratio of 480:1 to meet fluctuating hot water demand. A single heater might fire in the middle of the night to meet the demand for showers at that time, while all 24 might be needed a few hours later for the start of the day 

Benefits of Banking, Modulation 

Banking multiple units with modulating technology yields the following benefits for building owners and facility managers.

• Peace of mind through redundancy. Banking units means never having to worry about a faulty heater shutting down all hot water production. A banked system is designed to always meet hot water demand. If one tankless unit is down, the others will modulate appropriately to deliver the required hot water. If all remaining heaters reach maximum demand, the flow rate will be reduced slightly to lower the BTU input and maintain the set-point temperature.

• Less wear and tear. Since banked tankless water heaters fire only to meet present demand, and the load is equalized among those that do, each unit endures less strain over time. For example, instead of one storage-tank water heater operating for 10,000 hours, banked tankless water heaters that modulate to meet the same demand might each work for only 5,000 hours. All else being equal, each tankless unit in a banked system has a longer life expectancy.

Tankless units also acquire less sediment buildup. To further reduce the toll on the system, incoming water may be filtered to maximize quality. It is important to test and treat the incoming water to ensure maximum longevity and performance. 

• No standby losses. Storage-tank water heaters, whether condensing or noncondensing, incur standby losses. These standby losses, over time, can result in millions of wasted BTUs.

• Installation savings. Specifiers, installers and building owners may have concerns about the costs associated with installing multiple tankless units. However, a commercial tankless system’s upfront cost may be lower than its single, tank-type equivalent. 

It is also possible to supplement the tankless system with one or more storage tanks. This will allow fewer tankless units to be installed without losing the ability to modulate BTUs. There also is no need to oversize a tankless system as a safety precaution. It will consistently deliver the specified amount of hot water.

Some tankless water heater manufacturers offer prefabricated rack systems of varying sizes to make it easier to choose the banking option. The racking approach streamlines installation costs by preassembling, pre-plumbing and preprogramming multiple units in a standard manifold for a particular application. The rack can also come pre-engineered with isolation valves, as well as system and pump controllers. The net results are reduced installation labor costs and a much lower hassle factor for the installer and the end-user.

If condensing heaters are chosen, their cooler exhaust gases will allow for PVC venting — instead of stainless steel — further reducing costs. In warmer climates, an outdoor installation eliminates the need for

Addressing Concerns 

Most banked-tankless users have no major problems with this approach. However, installing multiple units rather than one will likely involve more labor and materials. That is, when installing two heaters as opposed to one, the contractor will likely be doubling the amount of plumbing, venting connections, etc. This probably seems obvious, as well as relatively easy to plan for, so the benefits of banked tankless outweigh the additional work. 

A prefabricated rack option helps simplify the installation process by reducing the number of plumbing connections required. In a rack system, each tankless heater’s exhaust can be placed into a single common manifold. The predesigned racks can incorporate from two to six prehung manifold water heaters, either wall-mounted or floor-mounted. 

All water piping, gas piping and condensate connections are positioned together. This provides a single point of connection for hot and cold water, gas and condensate. Fewer connections, of course, saves time and labor. The heaters will share common venting, allowing multiple water heaters to be installed into a single exhaust system. This can reduce the number of penetrations through the sidewall or roof of the building. 

For anyone considering banking tankless water heaters for a commercial application, reach out to manufacturers with questions. The No. 1 problem is incorrect installation. Referring to manuals and contacting the manufacturer for clarification will go a long way to minimizing, if not avoiding, installation errors. Maximizing the ease of installation and assisting system designers and installers is a top priority for all manufacturers. 

In addition, know your water quality before installation begins. If your area has hard water, commit to properly treating it. This will help extend the longevity of your tankless heater and reduce maintenance concerns.

Hot water supplies must never be compromised in a commercial application. If they are, building owners will face angry tenants, customers or clients at the very least. Even worse, health code violations can shut down operations. 

A banked tankless water heater system is a guarantee against such doomsday scenarios, especially in a pandemic. A well-designed, properly sized, professionally installed system ensures uninterrupted, cost-effective hot water supplies during those moments that count the most.