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Low-Flow Update, continued

Pumps and compressed air. Kohler offers another approach to power-assisted flushing with its Power Lite toilets (Figure 5). Instead of relying on vacuum or water pressure, these high-end models contain a small submersible pump that forces water from the tank to the bowl. The manufacturer claims that the resulting flush is comparable to that of a pressure-assisted fixture without the associated noise; the obvious limitation is the need for a GFCI-protected outlet within easy reach of the fixture. The Power Lite models also offer the user a choice of two flush volumes -- a standard 1.6- or a water-saving 1.1-gallon flush for liquid waste. A model with an electrically heated seat is also available.



Figure 5.Kohler's Power Lite series of toilets contain compact submersible pumps that are said to produce a flush similar to that of a pressure-assisted fixture. A GFCI-protected outlet is required to supply power to the pump.

Where the ultimate low-flow fixture is required, a California company called Microphor offers several toilets that provide an efficient flush on a mere 2 quarts of water (Figure 6). There's a significant catch, though: In addition to the usual water-supply-and-drain system, the Microphors need an external supply of compressed air at 60 psi.


Figure 6.Microphor makes two residential toilets that use a mere 2 quarts per flush. While the need for a separate source of compressed air makes this impractical for most applications, it's a useful option where local water restrictions or a low-yield well rule out conventional low-flow fixtures.

In a residential installation, that usually involves installing a hardware-store air compressor in the basement or garage and running a 3/8-inch copper line to the fixture, according to Microphor spokesperson Walt Hess. Hess claims that the air-assisted toilets are being used successfully in the California communities of Carmel and Monterey, where severe water restrictions are in effect, as well as in houses elsewhere that are served by low-yield private wells.

Considering Peak Flow

A key difference between pressure- and vacuum-assisted toilets and most gravity fixtures concerns something called peak flow -- the maximum rate at which water passes through the trapway of a given fixture during the flush cycle. Generally speaking, pressure-assisted units have the highest peak flows.

According to Frank Vullo, director of product management for Eljer, the company's pressure-assisted models have peak flows approaching 95 gallons per minute. (Because the entire flush consumes only 1.6 gallons, of course, that high rate of flow is sustained for only a fraction of a second.)

Toto claims that its 3-inch flush valve offers a rate of flow in the area of 50 gallons per minute, which Fernando Fernandez describes as "up there with pressure-assisted toilets." The average gravity fixture, he claims, tops out at about 30 gpm.

The exact figures may be open to question, but it's evident that the Totos and the pressure-assisted units do provide a characteristically rapid flush: Push the handle, and the contents of the bowl are sucked into the drain almost instantly, with little or no visible swirling action.

That sort of high-speed flush may mean fewer clogs, but manufacturers of gravity toilets based on the traditional 2-inch flush valve tend to downplay its value.

"They're all about forceful, and we're all about a sustained flush," says Kohler engineer Kathryn Streeby. Kohler's gravity fixtures, she contends, are designed to provide a relatively gradual flush that swirls water vigorously around the bowl during the drain cycle. According to Streeby, that still clears bulky waste effectively while also reducing streaking and leaving the bowl cleaner.

Rating Performance

All toilets sold in the U.S. are required to meet ASME standard A112.119.2M, which measures water-exchange and bowl-cleaning performance as well as the ability to flush several types of test media (Figure 7). But the fact that a given fixture passes the ASME tests doesn't necessarily mean that it will perform satisfactorily in the field.



Figure 7.To meet the minimum ASME performance standard, a toilet must successfully flush 100 3/4-inch polypropylene balls (top left) and a quantity of polyethylene granules (top right). A dye test (bottom left) and an ink-line test (bottom right) measure the fixture's ability to refill the bowl with clean water and pass enough water through the holes in the rim to minimize "skid marks."

"ASME is an absolute minimum," says Nick Quattro, director of marketing for Briggs Plumbing Products. "If you don't set the bar higher than that, you'll have a lot of unhappy customers."

Individual manufacturers conduct extensive in-house product testing, but the results are seldom made public in any meaningful way. Performance tests undertaken by consumer groups and public agencies, however, permit some worthwhile (though inconclusive) product-to-product comparisons.

Independent testing. A recent study by the NAHB Research Center is a good case in point. Under contract with two West Coast utilities -- Seattle Public Utilities and the Oakland, Calif., East Bay Municipal Utility District -- the NAHB researchers subjected 49 current models of popular toilets from 17 different manufacturers to a variety of laboratory tests. Among other things, the researchers evaluated flushing performance, flush volume, trap diameter, and water-spot area.

But the most controversial part of the report was what the researchers termed the "flush performance index" for each toilet, based on the average amount of test media remaining in the bowl after a series of test flushes. The scores for individual toilets ranged from a perfect score of 0 -- indicating no material remaining -- to a high of 82. (To establish a benchmark for what might be considered unsatisfactory performance in the field, the NAHB researchers also tested three used "problem toilets" that had been the subject of user complaints; these were found to have flush performance numbers ranging from 32 to 44.)

Of the 49 toilets evaluated by the NAHB researchers, 35 were found to have flush performance indexes of ten or under, which the report synopsis describes as a "reasonable criteria for selecting the better performing toilets." Taken at face value, those figures suggest that nearly a third of the fixtures on the market don't work very well.

Conflicting studies. The complete report, published on the NAHBRC website in October 2002, caused a furor in the plumbing industry. Manufacturers whose products were found to perform well looked for ways to use that information in their marketing efforts, while others sought to downplay the results.

"I don't want to knock the folks at the NAHB," says Peter DeMarco, "but I have a problem with any test that tries to rate performance using just one type of media. The type of media you choose can determine the results you get." Moreover, DeMarco claims, the NAHBRC test loadings, consisting of various combinations of floating and sinking sponges, were unrealistically heavy. "They were over the top," he says. "They were far above what a toilet would ever encounter in normal use."

Coincidentally, another independent evaluation of low-flow toilets appeared in the October 2002 issue of Consumer Reports magazine, about the same time as the NAHBRC report. A side-by-side comparison of the two suggests that critics like DeMarco have a point when they argue that different types of objective tests can yield different results.

Of the NAHB's ten best-performing fixtures, for example, the first nine were gravity models. One pressure-assisted toilet, the Gerber Ultra, appeared in tenth place. The Consumer Reports researchers, on the other hand, awarded their top eight spots to pressure- or vacuum-assisted fixtures, with two gravity models appearing in the ninth and tenth positions. The Toto Ultramax, which tied for first place with another Toto fixture in the NAHBRC rankings, ranked behind 20 of the 28 toilets evaluated by the Consumer Reports staff.

Researcher Bob Hill, who led the NAHBRC team, believes that the differences between the studies stem partly from the different test media and loading rates used, and partly from the fact that the Consumer Reports staff considered factors like bowl-washing ability, draining, bowl dilution, and noise in calculating an overall rating for each toilet.

"We looked at flushing ability, water-spot area, and flush volume," Hill says, "but didn't try to come up with a weighted average. Our intent was to put the raw data out there and let consumers draw their own conclusions."

Soon after the NAHBRC study appeared, however, the group began to worry that consumers might be drawing conclusions that weren't supported by the data. "When you rank products from top to bottom, the ones in the middle may be performing very well, but they look like they're far down the list," Hill says. "That can be misleading."

The full-length report, Water Closet Performance Testing, has been removed from the NAHBRC website (, which now contains only a brief synopsis of the results. The full report, however, can be downloaded in pdf form from a number of other sites on the Internet, such as

Cost and Value

Opinions vary on the relationship, if any, between how much a toilet costs and how well it works. After comparing performance data to retail price, for example, the NAHB researchers concluded that "there is no apparent correlation of price with performance." A number of toilets retailing for around $50 were found to perform very well.

Peter DeMarco is adamant that even very inexpensive toilets can perform well. "If the manufacturer is paying attention to quality control, cost shouldn't be a factor," he says.

Plumbers, on the other hand, tend to take a different view. Rex Cauldwell notes that most of his callbacks and installation problems seem to involve inexpensive builder-grade products. Burlington, Vt., plumber Dennis Deloy agrees. "If you buy a $39 toilet, you're going to get a $39 flush," he says. "I prefer Gerbers. They're about all I use, and I've never had any problems with them."

Terry Love observes that most of the models he's had consistent success with tend to cost $200 or more. "I install lots of different brands, but the new Totos are my favorites," he says. (Love's website,, contains his recommendations for specific models from American Standard, Gerber, Kohler, Crane, Universal Rundle, Eljer, Briggs, Mansfield, and other manufacturers, as well as comments from other plumbers.)

Old vs. new. Improved engineering has improved toilet performance overall during the past decade, but it's worth noting that not all of a given manufacturer's products will reflect the current state of the art. New products tend to appear at the high end, while older, less efficient ones are weeded out at the lower end.

"It's a good-better-best­type thing," says Toto's Fernando Fernandez. He notes that his company's Standard Gravity line, which dates from 1994, is still on the market even though two newer product lines -- which use the larger 3-inch flush valves and more sophisticated trapway designs -- offer superior performance.

"The 'good' product is the builder market," Fernandez says. "I leave it to the sales guys to convince them to upgrade, but I wish builders in general were more responsive to some of the recent advances."

Not surprisingly, most manufacturers show little enthusiasm for telling buyers which of their products use older technology. But knowledgeable suppliers will be able to provide that information, which may be worth knowing in cases where performance is an issue.

Installation and Adjustment

When a low-flow toilet clogs or fails to deliver a complete flush, the user often assumes that an old-style 3.5-gallon fixture would have handled the same situation with ease. This "good old days" mentality is frustrating to manufacturers, who are fond of pointing out that plungers weren't invented in 1992. Peter DeMarco notes that flushing is a chaotic, somewhat unpredictable event. "You can never completely rule out clogging," he says. "Sometimes the waste will just line up in a random way that completely blocks the trapway."

On the other hand, because modern low-flows are more precisely engineered than their predecessors, it's safe to say that they are inherently less tolerant of error. Plumbers and manufacturers alike stress the importance of proper installation, adjustment, and maintenance to trouble-free operation.

Controlling water volume. When the first underperforming low-flows hit the street in the early '90s, many plumbers quickly discovered that providing them with additional water made for a better flush. To avoid complaints and callbacks, enterprising plumbers often modified them to use something closer to the familiar 3.5 gallons per flush. Since most of those fixtures were 3.5-gallon models that had been adapted by the manufacturer to get by with less, this sort of in-the-field reverse engineering made sense and usually worked fairly well.

That's no longer true. If today's better-engineered toilets are flushed with too much water, their performance will get worse instead of better.

Rex Cauldwell notes that it's important to make sure the tank fills exactly to the manufacturer's fill line, and to adjust the level if necessary. The chain that connects the flapper valve to the flush lever, he finds, is another common source of problems. "If there's too much slack in the chain, it will lie on the flapper and make it close too soon," he says. "I like to have one or two links of slack when the lever is pushed down all the way."

Flapper flap. A typical flapper valve lasts about five years -- often less where in-tank bowl cleaners are used. When the original flapper wears out, the homeowner frequently replaces it with a generic flapper from the hardware store. This can mean trouble, because replacement flappers often release much more water than the original manufacturer-supplied valve.

In the NAHB tests, for example, all of the new toilets were found to use close to the mandated 1.6 gallons per flush. In a second round of flush tests, using generic replacement flappers, water consumption shot up to an average of nearly 3 gallons per flush. Other researchers have come up with similar results. To prevent customer dissatisfaction down the road, it's a good idea to stress the need to use the right replacement valve.

Low-Flow Toilet Manufacturers

Afeel Corp. / Huntington Brass


American Standard


Barclay Products


Briggs Plumbing Products


Crane Plumbing / Fiat Products


Eljer Plumbingware


Geberit Manufacturing


Gerber Plumbing Fixtures




Jacuzzi Whirlpool Bath








Liette International


Mansfield Plumbing Products




Neo-metro Collection




Renovator's Supply




Sloan Flushmate


St. Thomas Creations


Sterling Plumbing Group


Toto USA




Whitehaus Collection