Shake Shack serves elevated versions of American classics using only the best ingredients. It’s known for its delicious, made-to-order Angus beef burgers, crispy chicken, hand-spun milkshakes, house-made lemonades, beer, wine and more. With its high-quality food at a great value, warm hospitality and a commitment to crafting uplifting experiences, Shake Shack quickly became a cult brand with widespread appeal.

Henderson Engineers, the Kansas City-based national building systems design firm where I serve as the plumbing technical director, has provided design services for more than 135 of these locations. 

Sit-down dining is available at Shake Shack, but a significant amount of its business is through its digital and delivery channels. For patrons dining on-premises, food is served via individual serving-size cardboard boxes and paper cups on a metal serving tray. Hot water is used in the kitchen for preparing and cooking this food, as well as utensil clean-up and handwashing. 

On Shake Shack design and construction projects, the food service consultant provides a code-minimum, triple-compartment sink for manual pot and pan washing, along with at least three handwashing sinks. It also provides a double-compartment sink and a work sink in the coffee and tea prep area. 

Depending on facility size, one or two undercounter commercial dishwashers are provided by the kitchen equipment consultant for washing metal serving trays, utensils, and small pots and pans. While Henderson does not specify the hand sink faucets, our drawings specify the plumbing contractor to provide 0.5 gallons/minute (gpm) flow restrictors to conserve water and energy.

Most Shake Shack projects include men’s and women’s restrooms designated by the architect. Henderson specifies the women’s restroom with two water closets and the men’s with a single water closet and a urinal. We specify each restroom with a single wash fountain lavatory with an electronic single-temperature faucet for patron handwashing. These wash fountains are preferred by Shake Shack for their ease of installation, appearance and durability. 

For water and energy conservation, Henderson specifies 0.5 gpm flow restrictors at the wash fountain faucets. Since the faucet is a single temperature, nonadjustable type, we opt for an ASSE 1070 thermostatic mixing valve set at 100 F.

Water Heating System

For food service, our experts design a water heating system operating at the maximum code-allowed water temperature of 140 F for Legionella control. We designed the hot water recirculation system to return water back to the water heater at a minimum return temperature of 132 F, given that a temperature of 131 F is known to kill Legionella in four hours. 

Henderson uses constant flow cartridge-type control valves and constant-speed recirculation pumps because of their low first cost. Constant flow cartridge-type control valves require no calibrating and setting in the field by the contractor, thus limiting expenses for Shake Shack.

Initial project water heating systems consisting of two 80-gallon electric water heaters are provided for facilities where only gas is available for cooking or where there is no space for water heater flues. Two heaters are chosen for redundancy. 

Where gas is available for water heating, two 80-gallon, 150 MBH high-efficiency water heaters are provided. However, tank water heaters require a large footprint for installation and access. Henderson always ensures space is available to remove one water heater without disturbing the other for quick replacement.

Instantaneous Hot Water

In 2020, Shake Shack directed Henderson to provide instantaneous gas water heaters, which offer energy savings in the form of no standby losses from the storage tank. They also offer additional redundancy in that each heater can operate as a standalone heater if required. 

Each heater includes a bottom gas and cold water inlet and hot water outlet in addition to a combustion air inlet and exhaust outlet at the top. Because the water and gas inlets and outlets are located at the bottom of the heater, gas, cold and hot water headers are installed underneath the heaters. Henderson allows 24 inches of leeway to install the headers and isolation valves. 

The combustion air inlet and exhaust at the top of the heaters make them difficult to stack vertically, and we have learned the heaters are ideally installed in a row along the wall with the gas, hot and cold headers mounted below. Henderson provides 6 inches between each heater and 32 inches of open space in front of each heater for maintenance access. The combustion air and exhaust route straight up through the roof of the building.

Our first designs included wall-mounting the heaters in a row along a back-of-house corridor, as shown in Illustration 1. The bottoms of the heaters were set at 4 feet above the floor. The corridor acted as the service space, making them easily accessible for maintenance. 

However, installing the heaters in working space has the disadvantage of taking up valuable storage space and interfering with staff when maintenance is required. A more traditional approach is to install the heaters in a mechanical room.

One of our early Shake Shack designs included installing the water softener, brine tank and water filtration system under the wall-mounted heaters, as shown in Illustration 2. The water softener was partially within the maintenance area in front of the heaters; the height of the water softener, gas, and hot and cold water header raised the bottom of the heater more than 7 feet off the floor. 

While this setup saved floor space, it proved difficult when providing maintenance, which required accessing the heater with ladders and interfering with the water treatment system installed below. Alternatively, installing two heaters on one wall and two more heaters on the 90-degree adjacent wall allowed two heaters to share their access space, therefore reducing the footprint. The headers below the heater can be easily installed to make the 90-degree bend required.

Many instantaneous gas water heater manufacturers offer factory-assembled, prepiped and skid-mounted systems for four heaters mounted back-to-back. These packaged systems include hot, cold and gas headers with shutoff valves installed underneath the heaters for single-point connection. Factory-assembled exhaust and intake headers also are provided for single-point connection. 

These systems save contractors time in the field by providing a consistent method of installation. Henderson evaluated this option for Shake Shack equipment rooms and found the back-to-back installation with service space on both sides took up too much floor space, as shown in Illustration 3.

Another space-saving idea was to install water heaters with electric-resistance, freeze-protection heating systems on the roof. Henderson would minimize the amount of hot, cold and condensate piping on the roof, but specify the water and condensate piping to be insulated and provided with electric heat trace. This ensures that no damage occurs from freezing. 

The aforementioned factory-assembled, prepiped and skid-mounted systems are ideal for roof mounting; the skid system is designed to meet roof wind loads. As standard practice, our experts only specify heaters on the roof in mild climates with minimal potential for freezing since power failures can occur in snowy or icy freezing conditions, thus rendering systems useless.

Our Shake Shack construction management partners recommended a third-party manufacturer that makes prepiped skid-mounted systems with four stacked water heaters. The heaters are assembled with the upper heaters offset to the front to allow the lower heater’s intake and exhaust flues to pass behind. The lower heaters are installed close to the floor so that the upper heaters are not installed too high for access. 

A common gas, hot and cold water header is installed on the side of the assembly with a subheader installed below the lower and upper heaters. Space is saved by the sharing of access space of the upper and lower stacked heaters, as shown in Illustration 4. The side-by-side heaters fit in the mechanical room without an ion exchange water softener. The width of the heater assembly is kept to a minimum and can be installed in a 5-1/4-foot-wide alcove.

Shake Shack construction managers also evaluated all the instantaneous gas water heater installations. They chose to standardize on the wall-mounted installation above the water softener and filtration system, as shown in Illustration 2. This option took up the least floor space. It was determined that the instantaneous heater maintenance requirements could be met with maintenance technicians accessing them with ladders with few problems.

Water Treatment 

Shake Shack has a sophisticated water treatment system serving its beer coolers, custard machines, ice machines, carbonators, water glass fillers, and coffee and tea makers. Since Henderson’s field of expertise is not water treatment, the kitchen equipment consultant spearheads filter selection on each project. 

The consultant provides a central filter assembly with particulate prefilters and carbon adsorption filters in series to improve water taste. A third filter housing in series includes a scale inhibitor treatment cartridge. This filter assembly has two outlets. One outlet provides filtered water only; the second outlet provides filtered water with scale inhibitor. Water for all equipment except for the carbonator receives scale inhibitor. 

Henderson’s responsibility is to ensure the correct filtered water is sized properly and connected to the correct equipment, as indicated by the kitchen consultant’s drawings. We indicate the two waters in the legend and on our drawings per the legend below:

Generally, Shake Shack avoids ion exchange water softeners given their relatively high installation, operating and maintenance costs. The kitchen equipment consultant decides if an ion exchange water softener is necessary on a project-by-project basis. For scale control, softened water should be considered for all water heaters.

Instantaneous gas water heaters typically include a 0.375-inch Type K copper heat exchanger that can easily be clogged by scale. It’s common for such water heaters to be installed on restaurant projects without ion exchange water softeners. 

To prevent scale from clogging Shake Shack’s heat exchangers, Henderson specifies the heaters with the manufacturer’s recommended pretreatment system. This system consists of a water filter shell with media using template-assisted crystallization (TAC) technology to condition and control the scale. Ion exchange or TAC technology does not preclude requirements for regular manufacturer-recommended cleaning of the heat exchanger tubes.

Using instantaneous gas water heaters saves Shake Shack valuable floor space and offers water heating system redundancy. Like any other water heating system, consideration for mounting, piping and access space for maintenance must be accounted for. 

Finally, an understanding of the locality’s water hardness is necessary to aid in the decision between providing ion exchange water softening or water heater manufacturer-recommended TAC water conditioning. 

Warren Rosenbrook, PE, CPD, FASPE, is the plumbing technical director at Henderson Engineers, a national building systems design firm.