There are three main types of HETs, which operate slightly differently and yield slightly different water savings:
Dual-Flush: Dual-flush toilets save water by offering two different flush volumes, one for solids and one for liquids, so you save water by only using what you need. Most dual-flush toilets use 1.6 gpf for a full flush and 0.8 gpf for a reduced flush. Studies show these toilets average about 1.3 gpf.
Pressure-Assist: Pressure-assist toilets compress a pocket of air inside a sealed chamber as water fills. When flushed, the pressurized air forces the water rapidly into the bowl, creating a powerful, fast flush that has a “whoosh” sound. The flush can be slightly louder than standard toilets.
Single-Flush: A few manufacturers do offer HETs that utilize a single-flush—what many would describe as a “standard-style” toilet. These toilets use no more than 1.28 gpf.