Tank top flush toiletToilet Design, Types, Features, Installation

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Guide to the different types of toilets & toilet designs:

This article discusses the types of toilets available, features of gravity flush toilets, power-assisted toilets, vacuum-assisted flush toilets, and the properties of one piece vs two-piece toilets.

We also discuss how to stop or prevent sweating (actually condensation) on toilets.

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Design Choices & Alternatives for Toilets

Figure 6-4x: (C) J Wiley, S BlissAs noted in Chapter 6 of Best Practices Guide to Residential Construction:

[Click to enlarge any image]

When water-saving toilets were first introduced in the 1980s, they reduced water usage from 5 to 6 gallons per flush (gpf) to 3.5 with little effect on performance.

However, when Congress mandated in 1992 that manufacturers had two years to reduce water usage to 1.6 gpf, the engineering challenges were much greater.

Most early toilet models were essentially 3.5 gallon designs hastily modified with smaller tanks and narrower trapways intended to increase the flow rate. Most did not work well and required two and sometimes three flushes, negating much of the benefit to water conservation.

Better toilet design and new toilet technologies have led to greatly improved performance in some models. In addition to traditional gravity designs, two types of pressurized designs have been introduced: pressure-assisted and vacuum-assisted.

Both types benefit from the additional flushing power. However, with the pressure-assisted, the increased flush comes with increased noise and complexity (Table 6-11).

[Click any image or table to see an enlarged version with additional detail, commentary & source citation.]

Because there is no standardized testing, figuring out which models perform well is difficult. Test results on individual models performed by the National Association of Home Builders, Consumer Reports, and other groups are a useful guide, but results are not consistent due to differing test methods.

While all toilets sold in the United States must meet the American Society of Mechanical Engineers (ASME) performance standard A112.119.2M, this only guarantees basic functionality.

Operating Properties Gravity-Flush Toilets

This is the traditional method, which relies on water dropping from the tank to cleanse the bowl and start a siphon action in the trapway. Although the first low-flow gravity toilets had trouble, many of the newer models have been re engineered with higher tanks and larger trapways to improve the flush.

Some store three or more gallons in the tank to create greater pressure, but only let 1.6 gallons drain in each flush. One side benefit to this approach is less sweating in hot weather, since only a portion of the water in the tank is replaced with new cold water.

Gravity-flush models are generally easy to maintain, although they are a little more finicky than older 3.5 gallon models. For example, the water level must be accurately set for them to work as designed and worn out flapper valves must be replaced with the proper model rather than a generic one.

Among the gravity flush models that consistently rated well in independent tests are any of the Toto models that use its G-Max flushing system and the Kohler Wellworth and Santa Rosa.

Operating Characteristics of Power-Assisted Toilets

Widely used in commercial settings, these toilets have a sealed chamber in the tank that fills after each flush, using the home’s water pressure to compress the air trapped inside.With each flush, the compressed air forces the water down into the bowl with a loud whoosh, which is the primary complaint about these models.

As long as household water pressure is at least 25 psi, these are very effective at clearing the bowl. Since 1994 when the U.S. congress passed into law a requirement that new toilets use 1.6 gallons of water or less per flush, air, vacuum, or other pressure-assisted toilet flush mechanisms have increased in popularity and availability.

Because of the tank within a tank design of power-assisted flush toilets, as a side benefit, there is no sweating on the outside of the porcelain, but condensation and mildew can form on the surface of the power-assist unit.

While these toilets are not for everyone, they are particularly useful in retrofits where drainage is a problem, for example, where venting is inadequate or where the toilet sits at the end of a long drainage run with no fixtures upstream to wash the line.

When these toilets malfunction, the complete pressure-assisted unit is replaced. Power-assisted toilets cost about $100 to $150 more than comparable gravity models.

Examples of top-rate power-assisted toilet models include the Crane Economiser, American Standard Cadet PA, Flushmate (including a Flushmate III recall), and Gerber Ultra Flush.

For details about air, water pressure or other assisted-flush or power-flush toilets see LOW WATER USAGE TOILETS or go directly to FLUSHMATE TOILETS (within that article) where we discuss power-assisted flush toilets that also conserve water.

Also see water conserving or water saving toilets that use different flush volumes for urine than for solid waste, now discussed at TOP FLUSH TOILETS and at DUAL FLUSH TOILETS.

Also see TOILET TYPES, CONTROLS, PARTS for a complete inventory of types of toilets and toilet flush methods.

Operating Characteristics of Vacuum-Assisted Toilets

A relatively new design, these also have a sealed chamber. With each flush, a partial vacuum is created in the chamber, which connects to the trapway with tubing. The vacuum boosts the suction during the next flush, achieving a powerful flush but without the noise of a power-assisted unit.

Vacuum-assisted toilets use the same flush and fill valves as gravity flush toilets, making them easy to maintain. Only a few models are currently on the market, but they have performed very well in tests and are moderately priced at $50 to $100 more than comparable gravity models.

Among the top-rated models are the Briggs Vacuity 4200 and the Crane VIP Flush 3999.

One-Piece vs. Two-Piece Toilets

Toilet, one piece design (C) Daniel Friedman

Our toilet design photos compare a one-piece toilet design with a traditional two-piece (separate toilet tank and bowl) design.

The toilets shown were on display at Menards Lumber Supply in Duluth, MN. - DF

Toilet, two piece design (C) Daniel Friedman

One-piece units tend to have low sleek lines and cost substantially more than standard two-piece models where the tank is bolted to the bowl during installation (Figure 6-55 below).

Figure 6-4x: (C) J Wiley, S Bliss

Figure 6-55, Another example of a one-piece toilet unit.

One-piece toilet models are generally easier to clean, since there are fewer crevices between the bowl and tank to collect dirt.

With gravity flush toilets, it is harder for designers to achieve a sufficient head of water without the height of a standard tank, although redesigning other components has overcome this in at least some models.

[Click any image or table to see an enlarged version with additional detail, commentary & source citation.]

Sweating (Condensation) Problems on Toilets

Details about condensation on indoor plumbing pipes or fixtures are found

In humid areas with cold incoming water, sweating on the outside of the porcelain tank can be a significant problem, in some cases rotting the flooring around the toilets. Some of the new flushing strategies alleviate the problem somewhat:

One approach to avoiding "sweating" or condensation problems with older toilets is to add special foam insulation inserts inside the tank.

These may not work with low-flow designs, however. Also this does not prevent dripping from the bowl or water supply line. Where the problem persists, consider added an anti sweat valve (Beacon Valves) that tempers the incoming cold water with a little bit of hot water to bring it up to room temperature.

-- Adapted with permission from Best Practices Guide to Residential Construction.

This article series discusses current best design practices for kitchens and bathrooms, including layout, clearances, work space, and accessible kitchen and bathroom layout, clearances, turning space, grab bars, controls, etc. We include advice on choosing and installing kitchen countertops, cabinets, and kitchen or bathroom flooring, sinks, and other plumbing fixtures and fixture controls such as faucets.

A list of kitchen and bath product manufactures and sources is included. This article includes excerpts or adaptations from Best

Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.


Continue reading at TOILET TYPES, CONTROLS, PARTS - home, where we discuss the full range of types of toilets available. or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

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