Over my career, I’ve seen a multitude of different products and technologies developed to address challenges with plumbing systems and their construction. Some technologies never become viable or widely used; many are met with skepticism from plumbing engineers who typically prefer tried and true methods.

I’ve been skeptical of many technologies myself, and for years I viewed vacuum plumbing systems as little more than a passing fad. However, my attitude toward vacuum plumbing has changed, especially after it proved to be the only logical solution to several design challenges I faced.

Vacuum plumbing is an engineered drainage system that uses negative pressure supplied by source vacuum pumps to transport wastewater through piping that is typically smaller than that of gravity systems. Vacuum plumbing piping is often routed from fixtures up and overhead on the same floor that it serves. 

Instead of relying on floor penetrations and pipe slopes to move wastewater by gravity, the system uses vacuum source equipment consisting of pumps, receivers and controls with interface valves at fixtures to move the waste from the fixtures through the vacuum piping network from the fixtures it serves. Once the waste is transported to the vacuum source equipment, it is discharged to a gravity waste system. 

While this technology isn’t appropriate for every situation, it offers flexible routing, minimal trenching for gravity piping, reduced water consumption and localized disruption that can be especially advantageous in occupied buildings.

Vacuum plumbing vs. vacuum sewer

It is important to note that vacuum plumbing systems are not synonymous with vacuum sewer systems. They are two different systems with two different modes of operation. 

Vacuum plumbing systems typically operate at the building scale and use specialized water closets and fixture interface valves to isolate negatively pressurized piping from the fixtures. Vacuum piping is then routed from the fixtures and interface valves overhead to mains throughout the floor and then to the source equipment that discharges to a gravity system. 

Vacuum plumbing systems can be well-suited to renovation and infill projects in existing buildings, especially those that are sensitive to disruption to occupied areas and excavation of floor slabs.

Vacuum sewer systems are more often employed on a community or municipal scale rather than in a single building. Vacuum sewer systems use standard plumbing fixtures and drain by gravity to collection tanks that are often located outside individual buildings. 

These collection tanks have interface valves like those in vacuum plumbing systems and isolate the gravity drainage piping from the vacuum system. The valves open and evacuate the collection tanks when they reach a set fill level and then route the wastewater to a centralized vacuum equipment plant that then discharges to a gravity sewer. 

Vacuum sewer systems can be attractive in locations where groundwater, rock or environmental sensitivity make traditional gravity sewers costly.

Common misconceptions

Some engineers still view vacuum plumbing as an experimental technology, even though it has been successfully used for decades in healthcare, corrections, retail, education, airports and other markets. Other engineers have avoided vacuum plumbing systems because they believe that codes either do not allow or are overly restrictive about approving them. While most codes still have language that express a preference for gravity systems, many also have language around where and how vacuum plumbing systems can be implemented. 

Codes that do not include specific language for these systems often still contain sections on engineered systems and pathways for approving these systems.

In my experience, when plumbing plans include documentation from a manufacturer verifying that the vacuum system meets their recommendations, code reviewers are far more likely to entertain them. Furthermore, early discussions with code officials about these systems and how they address specific project challenges often yield favorable results. 

Finally, some engineers are concerned about the maintenance involved with the mechanical elements of vacuum plumbing systems. Like any engineered system, the station and valves require periodic attention; however, field evidence shows maintenance is modest in the early years — especially with proper commissioning and leak‑detection alarming at the station, as pumps cycle more frequently if air infiltrates the piping.

Applications, markets and advantages

Vacuum plumbing systems offer advantages in several markets. 

In healthcare, vacuum plumbing systems can provide another infection control feature, as gravity flush toilets generate aerosol plumes that deposit infectious material on nearby surfaces. 

The negative pressure associated with vacuum toilets keep these aerosol plumes far more controlled. Studies by the National Sanitation Foundation and several universities have found no detectable overspray around vacuum toilets versus measurable E. coli around gravity toilets.

Beyond healthcare, many buildings have elements that are sensitive to disruption by construction activities, and routing gravity waste piping through these spaces can be problematic. Examples include MRI and CT suites and other high-value healthcare elements, data and server spaces, food and beverage preparation and processing, and sterile areas that are intolerant of wastewater leaks from piping in ceilings. 

These areas can be avoided with vacuum plumbing systems, as the designer is relatively free to route the vacuum piping through less sensitive areas and on the same floor as the fixtures. Additionally, vacuum plumbing systems include wastewater containment and provide notification if leaks are detected. Small pipe punctures and joint failures pull air inward rather than expelling wastewater outward, while the source equipment generates an alarm when the pumps run for extended amounts of time.

Vacuum plumbing also offers advantages on projects with challenging construction costs, schedules and sequencing. Since most of the piping is routed overhead, plumbing contractors may not need to mobilize as early in the project and may have the advantage of working in a more controlled and conditioned area. 

As mentioned earlier, vacuum piping can be routed where best for the overall design since it is negatively pressurized and has fewer sloping requirements and has inherently smaller pipe sizes than gravity systems.

Finally, LEED buildings may be good candidates for vacuum plumbing systems, as they offer savings in water consumption. Vacuum toilets commonly flush at 0.5 gallons per flush (gpf) or less, while gravity toilets can flush at as much at 1.6 gpf.

Design: What to do and avoid

When considering a vacuum plumbing system, always engage the system manufacturer early. Despite the many advantages of vacuum plumbing systems, some projects and applications are not good candidates for them. 

For example, projects where wastewater could enter the piping at high temperatures can cause the liquid to boil in a vacuum, which can damage piping, interface valves and source equipment. Additionally, while vacuum toilets and valves have seen improvements in noise reduction over the years, they are still not good for noise-sensitive environments, such as sleep labs, recording studios and performance centers. Most manufacturers can advise you on whether your project is a good candidate for their system.

Manufacturers can also advise you on required pipe sloping, which can vary system to system. While vacuum mains do not have sloping requirements as restrictive as gravity systems, they do typically need intermittent rises in the piping to navigate around obstacles. 

Applications that are notorious for the volume and types of debris that get flushed into a gravity plumbing system include correctional institutions, behavioral healthcare facilities, and multi-dwelling residential sites. This debris can, and frequently does, lead to mainline blockages, which can disable operations in portions of a building, and in some cases an entire building itself.

Vacuum plumbing systems, with smaller diameter piping and normally closed failsafe waste interface valves, help avoid mainline blockages by preventing the debris from entering the drainage piping network in the first place. The debris is typically trapped at the vacuum interface valve. While that may disable a single fixture, the remaining fixtures and the building will continue to function normally. Importantly, the cost and time to remedy debris obstructing a single vacuum fixture is a fraction of what it takes to identify and clear a mainline gravity plumbing system blockage. This is especially important for facilities with failing or compromised underground piping.

When setting requirements for the source equipment, keep redundancy in mind. Manufacturers can give recommendations around this, but you should also consult your client on their risk tolerance. 

Designing the source equipment with N+1 pump redundancy is a given, and dual receiver tanks can also be a good idea. Alarms should be connected to the building automation system and immediately notify someone in the event of trouble. Additionally, source equipment should be connected to emergency power wherever possible, and some code officials mandate this.

Finally, educate your client about the maintenance involved and make them aware of the required frequency. Many manufacturers offer maintenance plans, which remove liability from the owner and puts less pressure on their facilities staff.

While vacuum plumbing systems are not appropriate for every building project, they do offer advantages for many of them. Occupied buildings that are sensitive to construction disruption can be good candidates for these systems, as they allow the disruption to be more localized and isolated to a single floor. 

Additionally, projects where speed to market is critical, such as many in healthcare, can see accelerated construction schedules due to less excavation and more flexibility in waste pipe routing.

While some plumbing engineers are still skeptical of vacuum plumbing systems, even more building owners are due to their unfamiliarity with them. So engage your client early in the process and be prepared to educate them on both the advantages and the potential risks.\