What are High Efficiency Toilets (HET)

High Efficiency Toilets

High Efficiency Toilet may sound like a strange phrase to apply to such a mundane home appliance. No doubt there is some hype in its use. But HETs, as they’re known in the trade, really are the “hot rod” version of this traditional home fixture. A little investigation shows why.


The definition of an HET isn’t just a matter of common industry agreement, at least not anymore. It’s also a matter of law. The U.S. Federal government many years ago set standards that have been adopted – and sometimes even exceeded – by the individual states.

Among other criteria, that means a water use of no more than 1.6 gallons per flush. In some states like California it’s even more stringent, as little as 1.28 GPF. In the latter case, those toilets that comply qualify for the government’s WaterSense label, something many manufacturers have taken advantage of for marketing purposes. In either case, its meaning is simple. Every time you press the handle or button, the toilet uses no more than that amount of water to dispose of waste.

Of course, there are many ways to accomplish that goal.

Gravity Feed Toilets

One method is the old-fashioned, been-around-for-decades, technology now called “Gravity Feed”. That is, when you press, a valve opens up and gravity forces water down a tunnel. The resulting pressure forces waste down another, lower, tunnel called a trapway.

It has its pros and cons.

On the upside, it’s certainly reliable. It’s been in use and real-world tested in millions of homes for decades with only occasional problems. On the other hand, for most of that time it has been used with tanks and mechanisms that supply 3.5 GPF or even more. Some older toilets used as much as 5 gallons per flush.

The downside becomes apparent when you combine that traditional design with the newer water-conservation restrictions. Sometimes, 1.6 gallons of water just doesn’t supply enough force to completely remove all the waste in one flush. Requiring a second flush defeats the purpose, but better that than the unsightly, unhygienic consequences of leaving some waste behind.

Dual-Flush Toilets

A step up in effectiveness is the dual-flush design. This high efficiency toilet earns the name by offering two ways to eliminate waste, usually by the use of two separate buttons to press. Press one and, in one sub-type, only about 1.3 gallons is released. That works fine for removing liquid waste. Pressing the second (or both buttons together in some instances) and 1.6 gallons is released.

Other models vary the technique. Some use as little as 0.8 GPF to 1.1 GPF. Some allow for a more traditional-style handle but one that can also be pulled up rather than just pushed down. Move it one way and you get the partial flush; the other way releases the larger amount of water.

Pressure Assist Toilets

The next step up, in the sense of efficiency and oomph, is the Pressure Assist design. Here, the toilet doesn’t rely solely on gravity (as do both the Gravity Feed and many Dual-Flush models) but adds artificially-generated pressure. Typically that’s supplied by a plastic or metal canister that holds air. When you flush, the air adds additional pressure to that supplied by the force of gravity.

The combination is impressive. Some models will force a small bucket of golf balls or short rubber tubes down the trapway. They can typically handle 40 feet of toilet paper in a single flush without jamming. Solid human waste is no challenge to these units.

Still, they have a downside. They don’t have motors that create the pressure and they put extra stress on your pipes. Those two facts imply two more: your home water system must supply adequate pressure in the first place and your pipes must be able to withstand the flush pressure. Fortunately, most homes satisfy those requirements, especially those built in the past 40 years.

Power Assist Toilets

A less-common variation on the HET theme is the Power Assist design. It actually incorporates a pump that forces water at higher velocity than is possible from a gravity feed or simple pressure assist method. The flush volumes are usually between one and 1.3 GPF, so they satisfy the legal restrictions.

However, this type typically requires a 120 volt electrical source to power the motor that drives the pump. While they’re safe, many consumers don’t feel comfortable having a water device like a toilet so directly connected to an electrical supply. They’re also generally much more expensive and usually overkill for homeowners. As a consequence, they’re more often found in commercial establishments and even there they are relatively rare.

Are HETs Worthwhile?

Whatever the specific method or design used, some questions arise. Is any High Efficiency Toilet worth the trouble and expense? What is the price difference, on average, between an HET and a regular toilet? Does my home really need this? Am I legally required to get one?

Naturally, the answers can vary from home to home but the following are valid guidelines for most potential buyers.

The Law

First, the legal issue. The short answer is “yes (and no), it does (not) apply to you”. Sorry for that but it does depend. The Federal guidelines apply to every state in the U.S. but you may be reading this from somewhere else. You’ll no doubt have other regulations to follow. Such is modern life.

The slightly longer answer is that it does apply to every state, but every state may have even more stringent requirements. Arizona and California, for example, tend to be more strict about water conservation than states like Idaho where rainfall (and snow) is more common and water more plentiful.

Those stricter areas tend to use more WaterSense designs. That label is applied to many toilets that meet the EPA’s guideline of using no more than 1.28 GPF. They also must remove at least 350 grams of waste in one flush. But rather than going over all the guidelines in detail and matching against the model that interests you, just look for the WaterSense label.

More generally, rather than trying to become an expert on the subject, which will interest few buyers who are just seeking a new toilet, simply rely on your preferred manufacturer and vendor. You can be sure they’ll follow the law. They’d be out of business pretty quickly if they didn’t.

The Cost

The other questions are actually of more urgent interest to most potential buyers. Whether an HET is worth the extra trouble and expense depends on individual factors too, but those are much simpler.

Most HETs – whether Dual-Flush or Pressure Assist, the two most common types – tend to be about $100 more than the average Gravity Feed model. That varies widely with specific model, of course, but that’s usually the floor. It goes up from there. It’s possible to buy a hugely expensive gravity feed unit, too, but comparing apples to apples on design that’s about the minimal difference.

On the other hand, an HET can easily save you enough water to make up for the extra cash in as little time as one year. Roughly one-third of the water used by the average homeowner used to go down the toilet. An HET can save roughly 10% of the water used by a standard toilet, even one restricted to 1.6 GPF. At today’s utility rates, for a family of four the amount of water conserved by an HET in one year can add up to the difference spent.

The Complexity

Still, HET models can require slightly more knowledge to install. Usually the mechanism inside makes no difference to you. But, in the case of a Power Assist there are, obviously, electrical considerations. Even with the Pressure Assist you have to take care, though. Measuring the pressure available, for instance, is a must. Estimating the pressure your pipes can withstand is also important, and not easy for the average do-it-yourselfer.

The Bottom Line

The bottom line, before you even think about acquiring the more complex type of toilet there’s the basic question: do I need it?

HETs are great technologically; they’re a definite advance over the traditional gravity feed model that uses or used 3.5 gallons per flush. I include “uses” because older homes may still have one; the law only took effect about 20 years ago. Still, they have their downsides. Gravity feed toilets have been around for generations; they’re tried and tested.

You can tell you might need a high efficiency toilet if: (a) you’re legally obligated by your state based on the age of the home/toilet you are installing/replacing, (b) you have a need for a high-force, low-water-use toilet. In the second case, that amounts to judging whether your family uses lots of toilet paper, the toilet is in very frequent use by lots of people, and so forth.

Purchasing a High Efficiency Toilet doesn’t have to be complicated though. Just look through the reviews and select the one that suits you best.

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