How Tankless Toilets Work

Tankless toilets, also known as flushometer or direct-flush toilets, operate without a water storage tank. Instead, they rely on a high-pressure flushometer valve to deliver water directly to the toilet bowl when needed. This on-demand water delivery allows tankless toilets to conserve water while still providing a robust flush.

When the flush handle or sensor is activated, the flushometer valve opens to allow high-pressure water to enter the toilet bowl. This creates a strong siphon effect that evacuates waste and quickly refills the bowl. Once complete, the valve closes to stop the water flow until the next flush.

Internal Components and Mechanisms

Flushing Mechanism

The main flushing component in a tankless toilet is the flushometer valve. This brass valve has an inlet to connect to the water supply line. When activated, it lifts open to allow pressurized water to flow into the toilet. The high-pressure water creates a strong siphon effect that clears the bowl contents.

A diaphragm or piston inside the valve controls the water flow duration to prevent overflow. Most flushometer valves provide 1.6 gallons per flush but can be adjusted to use less water if needed.

Water Delivery System

Tankless toilets require a dedicated high-pressure water delivery system to generate an instantaneous robust flush. This usually demands 3/4-inch or 1-inch supply pipes instead of the standard 1/2-inch pipes in most homes.

Larger pipes allow the flush valve to deliver over 2 gallons of water per second at pressures between 25-80 PSI. Without this high-pressure supply, the flush would be weak and ineffective at clearing waste from the bowl.

How Users Activate the Flush

Sensor Detection

Tankless toilets utilize sensor-activated flushing instead of a manual handle. An infrared sensor is mounted on the tankless casing near the bowl and detects when a user has moved away after use. This signals the flushometer to open its valve for the preset duration.

Sensors come pre-calibrated to avoid false activations, like from a user's hand movements. Sensitivity can also be adjusted to flush at the optimal moment for water savings.

Water Flow Initiation

When the sensor detects the user has moved away from the bowl, a signal actuates the flushometer valve to begin the high-pressure water flow. This typically occurs within 2 seconds after the user steps away.

The pressurized water creates a siphon effect that forcefully evacuates the bowl contents while simultaneously refilling with clean water. After the preset duration, the valve closes to stop the flow until the next sensor-detected activation.

Continuous Water Use and Pressure

On-Demand Water Heating

Some tankless toilet models utilize on-demand water heaters to provide instantaneous hot water. When the flush sensor activates, heated supply water enters the flush valve. This allows the toilet to deliver piping hot water for a robust and sanitizing bowl rinse.

On-demand heaters only run when needed, helping cut energy costs. They also prevent lukewarm water issues seen with traditional tank style toilets.

Consistent Water Pressure

The closed flush valve design also maintains full upstream water pressure compared to traditional ballcock fill valves. This consistent high pressure allows tankless toilets to deliver strong flushes repeatedly without any degradation in performance.

Municipal water supplies generally provide all the pressure needed for tankless operation. In some cases, a booster pump on the building's water supply line may help optimize pressures.

Water Conservation Benefits

Lack of Storage Tank

Tankless toilets save significant water by eliminating tank storage between flushes. Traditional gravity flush tanks hold 2-5+ gallons constantly. Much of this ends up leaking down the overflow pipe due to slight tank leaks.

In contrast, tankless toilets only use water when flushing. No storage means no leakage between flushes. Some models use pressurized air tanks to maintain supply pressure instead of actual water storage.

Water Used Only When Needed

During each flush, tankless toilets flow high-pressure water for a preset duration, typically 1-3 seconds. This provides just enough water to siphon waste out of the bowl. Flow stops immediately afterward.

In comparison, tank style toilets empty a fixed 2-5+ gallon volume with each flush, whether the bowl is full or not. Tankless models add no unnecessary water, helping conserve supply.

Installation and Service Requirements

Pipe and Venting Requirements

A dedicated high-pressure supply line must be installed to support tankless toilet operation. In some retrofits, this demands re-piping with larger diameter hot and cold lines. Vent stacks may also need upsizing to handle the rapid high-volume flushes.

Using the existing undersized supply infrastructure can damage the flushometer system. Low pressures below 25 PSI would likely result in an inadequate siphon and unhygienic conditions.

Electricity or Gas Supply

Electrically-powered pump systems may be needed in cases of inadequate municipal water pressure. These ensure each flush delivers a robust 2+ gallon per second flow rate. Hardwired electrical connections must be made to power the recirculation pumps.

For tankless models using on-demand water heaters, either electrical or natural gas connections must be provided. These allow continuous heating to supply piping hot water the instant a flush is activated.

Maintenance Requirements

Descaling and Flushing

Periodic descaling using citric acid removes any mineral deposits from the flushometer valve or water jets. Any debris around the flush sensor is also cleaned to prevent false readings.

A full system flush can purge sediment and mineral buildup inside supply lines and valves. This protects critical toilet components from fouling or reduced flow issues.

Periodic Inspections

Routine inspections examine the physical integrity of internal seals, gaskets, and pipe connections. Worn diaphragms or fill valve seals are replaced to prevent water leakage.

Sensor functionality and timing are also validated to ensure flushes correctly activate based on user movements. Any detection issues can be remedied through sensitivity adjustments.

Costs and Benefits Compared to Tank Toilets

Tank Toilets vs Tankless

While tankless toilets carry a 30-50% higher upfront cost, their lifetime ownership costs can be less than traditional tank-type toilets. The main benefit is significantly lower water usage, with consistent water savings yielding a return on investment over time.

Maintenance needs are comparable for both toilet types, provided high-pressure line requirements are met for tankless models. Overall reliability is also similar with a projected service life of 15-20 years on major components.

For commercial applications, tankless toilets offer faster user turnover and continuous peak flushing performance. Hundreds of daily flushes do not degrade their functionality or siphon efficacy over decades of use.

Even residential tankless toilets can save the average family 9,000-15,000+ gallons per year. This conservation benefit offsets higher purchase costs over time via lower utility bills.