Water Closet Survey - 4/1/2002 - Home Interior Exterior

Water Closet Survey

INTRODUCTION

The NAHB Research Center undertook a Water Closet Survey in June 1999 in an effort to gauge consumer satisfaction with low-flow toilets and to characterize the nature of that satisfaction or any problems associated with the fixtures. The responses demonstrated a need to investigate further the toilets' ability to remove solids from the bowl. The primary issue for builders was service call complaints from recent homebuyers about frequent clogging.

The NAHB Research Center conducted research to develop a testing protocol to assess a toilet's ability to remove solids. Given that current standards do not provide adequate performance measures, the Research Center developed a "clog potential index" to measure flush strength. Used "complaint toilets" were evaluated to provide a reference baseline for the index. In addition, the Research Center purchased the three most popular toilet models from nine manufacturers and tested them according to the clog potential index protocol. All of the toilets noted in this report are close-coupled or one-piece gravity flush types; the research did not evaluate pressure-assisted models.

[Note: Low-flow toilets consuming no more than 1.6 gpf are mandatory pursuant to a U.S. Department of Energy regulation promulgated after passage of the Energy Policy Act of 1992.]

BACKGROUND

Types of Toilets and Features

All toilets must comply with the Energy Policy Act of 1992, which requires that units use no more than 1.6 gallons of water per flush. Water conservation initiatives have led to the redesign of toilets in various ways. Some manufactures offer dual-flush models that provide 1.6 gpf for solid waste and a smaller volume for liquid waste. Other designs use a pressure-assisted jet of water, mechanical augers, and various hydraulic designs. This report considers only gravity flush toilets, either one- or two-piece designs.

Standards and Code Compliance

Plumbing codes require conformity to ASME A112.19.2 for vitreous china fixtures and ASME A112.19.6 for hydraulic performance. These standards provide criteria for performance, hygiene, workmanship, strength, and suitability for use. Manufacturers provide third-party certification documentation of these standards when requested.

The ASME A112.19.6 (1995 Edition) hydraulic performance standard is currently undergoing revision. The test protocol for evaluating removal of solids has not been updated since enactment of the Energy Policy Act of 1992 and is currently considered inadequate.

Toilets that conform to ASME A112.19.6 may be code-compliant, but flushing performance could be inadequate. From the user's perspective, a unit should remove solids with one flush and, under normal use, should not clog. Until the standard is updated (estimated activation year 2002), there is no assurance that code-compliant toilets will perform adequately in removing solids from the bowl. For this reason, the NAHB Research Center developed a clog potential index by using a variation on the ASME bulk media and test protocol.

The study did not consider all the attributes typically evaluated when a toilet undergoes third-party conformity assessment to ASME A112.19.6. If these attributes are important, the reader is advised to contact the manufacturer for additional information.

TEST PROTOCOLS

Mixed Media Clog Potential Test

The NAHB Research Center developed the test and calculation methods used in this report to evaluate clog potential. The goal of the test protocol was to determine a performance index by challenging a toilet's ability to flush increasing amounts of bulk media. The challenge level should be adequately robust to detect performance differences between toilets.

Figure 1

Background. The test setup called for a calibrated water supply providing 20 psi static pressure and 8 psi flowing pressure at 3 gpm. Before testing, each toilet was calibrated in accordance with the manufacturer's recommendations to provide the rated flush volume. All tested units were adjustable to no more than 1.6 gpf.

The test media consisted of various numbers of sponges and four paper balls (see Figure 1). The media are a modification of experimental test media under development by the working group of ASME Standard A112.19.6–Hydraulic Performance of Water Closets.

Test Media Challenge Level. Figure 2 shows the sponge and paper test media compared with published data on fecal material density and mass of healthy adults. The test media consisted of floating and sinking sponges at five challenge levels. The challenge levels I, II, III, IV, and V correspond to four paper balls and 7, 10, 15, 25, and 30 sponges.

Figure 2

Clog Potential Index. The bars in Figure 3 indicate clog potential and represent test media that remained in the bowl after an initial flush for the ten series of challenge levels-five floater series and five sinker series. More than 100 flushes per toilet were made during the test, or approximately ten flushes for each challenge level for both floating and sinking test media. A perfect score is represented by zero, where no test media remained in the bowl; the maximum possible score is 214.

Please note the following regarding Figure 3:

• Arrows on the chart designate used toilets. All of the other toilets were purchased. Owners of toilets 33, 40, 42 and 43 reported frequent clogging problems with those units.
   
• Toilet 33 was not correctly adjusted when it was in-service. This toilet was evaluated twice, at its in-service condition at 1.2 gallon per flush (gpf), and as toilet 11 at 1.6 gpf. The clog potential improved at the correct flush volume, indicating that flushing strength and clogging can be caused by low tank water depth.
   
• Toilet 1 was included as a reference point for older vintage toilet design of 3.5 gpf. The owner reported satisfactory performance for this toilet.

Figure 3

Calculation Methodology. The clog potential index graph includes both types of media. The floating and sinking media data were combined by calculation.

Fully saturated sponge media were placed in the bowl, four saturated balled-up papers were the placed on top of the sponge media, and the mix was then flushed. The test media remaining in the bowl were counted and recorded. All remaining media were cleared from the toilet before the next repetition. Repetitions were performed at the same challenge level. A running average was calculated at the end of each flush.

The repetitions continued until a clog-index-stability criterion was satisfied. The criterion required the change in the running average to be 5 percent or less for five repetitions in succession. The testing at each challenge level was terminated when a clog-index-stability criterion was satisfied.

The process was repeated for all challenge levels. The ten running averages (five for sinking media and five for floating media) were added together for the clog potential index. The clog potential index shown in Figure 3 was determined by this calculation methodology.

Figure 4 shows an example of the clog-index-stability process for a test at the Level V challenge.

Figure 4

As noted in Figure 4¹, variability in a single flush test is brought under control as the number of test repetitions increases. Early in the test, the clog potential index was 34, but the index stabilized at 20 as noted by the line on the graph.

Price versus Performance

Yet another comparison was based on purchase price and performance. Figure 5 displays the retail purchase price and the clog potential index. Remember that a perfect performance score is zero such that the toilet flushes all the media for each challenge level. Figure 5 reveals no relationship between performance and price.

Figure 5

¹Repeatability and Error Estimate. Confidence interval and repeatability of this test method were evaluated with six technicians conducting eight repetitions; the mean of their results was 98.7. At the 95 percent confidence level, the upper limit was 119.1 and the lower limit 78.3. The error band is approximately ±20.7 percent about the mean.