Designing the plumbing for a commercial kitchen can be complicated if you don’t know the specifics.

I received a phone call from a developer who asked for assistance with the plumbing for a new restaurant. After a few minutes of discussion, I realized that there was not one restaurant, but two.

The building in question is 8,000 square feet with six tenant spaces. Three of the tenant spaces are intended to be a white tablecloth restaurant. Two of the spaces are for a quick-food-type restaurant, such as a pizza parlor.

My curiosity was piqued when I asked, “What kind of white tablecloth restaurant?”

The response was not what I expected. He said, “We don’t know.”

“You have to be kidding,” I responded. If you don’t know what kind of restaurant, how is anyone supposed to design the plumbing system?

“Do you know what type of kitchen equipment will be installed?” I then asked. “Do you know the size of the commercial kitchen anticipated? Do you know how many sinks are needed? Do you know where and what type of dishwasher?”

The answer was, “No, no, no and no.”

Designing In The Blind

Basically, the plumbing design for this white tablecloth restaurant would have to be done in the blind. There is no information that can be provided. You may want to walk away from such a project, but then again, work is work.

Is it possible to design and install a plumbing system for a white tablecloth restaurant without knowing any of the specifics? Yes, but you may not get everything right.

The first thing I listed was all of the fixtures that would be necessary for such a restaurant. At a minimum, a commercial kitchen needs a three-compartment sink. The nicer, the better. There also needs to be a hand-washing sink. Most likely, a dishwasher will be installed. Of course, with any food-handling establishment, there will be a grease interceptor. One would also guess that there will be a refrigerator and freezer.

These are the basics. There could be many additional water-using and drainage-discharging fixtures. There are kettles, potato peelers, food waste grinders, pre-rinse, prep sinks, etc.

You need to locate the plumbing for these fixtures and appliances using a best-guess method. The first thing to consider is that certain fixtures and appliances must be located under a commercial kitchen exhaust hood. Any dishwasher, other than an under-the-counter type, must be located under a hood so that the steam can be exhausted. Certain kettles and appliances also may have to be installed under a hood.

While this is a code requirement - found in the mechanical code, not the plumbing code - there are instances when an exhaust hood is not necessary. When the HVAC system takes into account the increased humidity from the kitchen equipment and appliances, certain steam-generating fixtures and appliances do not have to be located under an exhaust hood.

When designing the drainage system, I am of the opinion that there are never enough floor drains and floor sinks. The ideal selection for the floor fixtures is a combination floor sink/floor drain. These are the fixtures that the various manufacturers design to be converted to a floor sink when necessary. Otherwise, they are a floor drain. Anywhere it appears that appliances, fixtures or islands may be located, a floor sink should be installed.

When sizing the drainage piping, a commercial kitchen is a location where bigger is better. Normally, I always advise that keeping a drain smaller is better. However, with a commercial kitchen, there is always the possibility that a tremendous amount of water is discharged within the same period of time. For this white tablecloth restaurant, I recommended a minimum of a 4-inch drain below ground, with consideration for a 6-inch drain. Again, you never know.

I suggested a number of rough-ins of 2-inch drains for various sinks or dishwashers. The more difficult determination is which of these drains to design for discharging through a grease interceptor. With the recent changes to the plumbing codes, it is best to plan on piping everything to a grease interceptor. Dishwashers can now discharge to a grease interceptor. Similarly, food waste grinders may discharge if there is a solids interceptor ahead of the grease interceptor.

As for the design of the water piping system, again, bigger is better. Even though this white tablecloth restaurant is small in size, the minimum water piping size would be 1 inch. Consideration can even be given to providing a 1 1/4-inch water supply. Rather than a 1/2-inch supply to each sink or appliance, I provided a 3/4-inch supply. This will allow fixtures and appliances with greater water demands to be satisfied with the prepiped system.

When the water heater is considered, the easiest solution would be to pipe the water heater but not install one. Sometimes this is a viable option. However, with this developer, they want to show any prospective lessee that the water piping system is ready.

I selected a 125-gallon water heater. White tablecloth restaurants always have a high demand on hot water in a short period of time. The smallest size I considered was a 125-gallon, tank-type water heater. If more hot water is required, there can either be another tank-type water heater installed, or an instantaneous water heater added locally for the fixtures requiring additional hot water demand.

After doing all of this layout, I provided one final comment to the developer. No matter what is installed, something will be wrong. So any lease agreement must include a statement of providing the best known plumbing system for the commercial kitchen.

By adding flexibility to the piping system, it makes it easier for a lessee to modify the kitchen. This flexibility will cost the developer a higher initial cost, but this is the price that they must pay for not having all of the information regarding the restaurant.