Pressure-Assist Toilets

by Nick Gromicko, CMI®
Pressure-assist toilets are water-efficient alternatives to standard, gravity toilets.  As they become more common, especially in newer and updated homes, inspectors should know how they work. Pressure-assist toilet
The first pressure-assist toilet was developed in 1984 in response to concerns over water shortages, and they have become progressively more powerful and economical. Other “green" or water-conserving toilet designs, such as dual-flush and composting toilets, are also available to the consumer, although gravity toilets are still favored in most situations.

Pressure-assist toilets look similar to gravity toilets from the outside, but inside their ceramic tanks, they appear and operate quite differently. As the building’s plumbing fills the tank with water, an air-filled diaphragm inside the tank shrinks accordingly. When the toilet is flushed, the compressed air functions like a spring, pushing the water into the bowl with significantly more force than is created by gravity alone.

Advantages of Pressure-Assist Toilets

  • They are less likely to allow clogs than standard gravity toilets. Because air pressure works in addition to gravity, trapped material is dislodged more easily.
  • There is no condensation buildup during humid weather, thanks to their tank-inside-tank design.
  • They are less likely to break or require maintenance because there are fewer moving parts.
  • Their strong flushing ability is well-suited for older homes where additional force is required to push waste through old pipes.
  • Pressure-assist toilets are more water-efficient.  They typically average 1.1 to 1.2 gallons per flush, which is less than dual-flush toilets, which require 1.3 gallons per flush, or single-flush gravity toilets, which require 1.6 gallons per flush. The U.S. EPA estimates that if you replace your home’s pre-1994 toilet with a pressure-assist toilet, you can save 4,000 gallons of water per year.
  • Some local utilities across the United States offer rebates for replacing old toilets with pressure-assist toilets, or other high-efficiency designs.

Disadvantages of Pressure-Assist Toilets

  • A great deal of noise is created by the sudden rush of water and air moving through the bowl, which may be a concern in residential settings. The noise lasts only a few seconds, however, and newer designs have mitigated this problem.
  • There may be some difficulty in obtaining replacement parts. Many hardware stores don’t carry parts for pressure-assist toilets, and the parts may seem foreign or unfamiliar to most homeowners.
  • The initial financial outlay is greater, since they are more expensive than gravity models.
  • They require at least 20 to 30 pounds per square inch (psi) of pressure, which may be an issue in homes with low water pressure. Ask your InterNACHI inspector about this during your next home inspection if your pressure-assist toilet lacks sufficient force to remove waste completely.
  • The high-velocity jet will shred waste or paper, which may float back into the bowl and require a second flush.
  • Their typical two-piece construction may be less aesthetically pleasing than conventional designs.
  • The trip-lever activation usually requires more force than is required by gravity toilets.
  • A pressure-assist toilet cannot be converted to a gravity toilet.
In summary, pressure-assist toilets are a type of green toilet design that can be preferable to conventional, gravity toilets.  They are becoming increasingly popular for environmental reasons, and some HOAs and municipalities actually require them, especially for new construction.   Inspectors should become familiar with how they work, and the potential problems they may encounter.