Tankless Water Heaters - General Description





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GENERAL PRODUCT DESCRIPTION

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SIZE: Tankless Water Heaters are manufactured in two basic sizes, a large four-chamber unit (15 _" x 15 _" x 6 _") and a smaller two-chamber unit (15 _" x 10 _" x 6 _"). The same advanced microprocessor technology and thermoplastic construction are used in both sizes. Therefore, many of the parts are interchangeable.

MODELS: There are three models of each size available. The four-chamber models are RA-18, RA-22, & RA-28. These models are designed generally for domestic water heating in whole house and booster applications. Also, the two-chamber models are RA-9, RA-11, & RA-14. The two-chamber models are designed for space heating applications and point-of-use in commercial applications. The available models and their descriptions are listed on pages following this section. Refer to Tankless Water Heater Applications for more design and application details.

FEATURES: There are no moving parts or flow restricting devices used in tankless water heaters. They uses a unique flow/no flow detection system utilizing it's temperature sensors for flow detection. In standby, the heater maintains a very subtle temperature gradient and flow is detected when there is a change in the gradient. The advanced microprocessor control turns the power on through a set of relays and turns the power off when flow stops. The most important feature may be the patented "Power Sharing" technology which provides for evenly distributed power to the heating elements. This in turn, helps eliminate scalding potential, scaling and sediment build-up. Also, the control logic allows the power level to vary which is beneficial in minimizing the use of power for periods of less demanding usage.

CONSTRUCTION: The heating chambers are modular and molded of light weight thermoplastic materials. The chamber is specifically engineered for durability in harsh water heating environments and capable of withstanding extreme temperature swings and pressure changes. Heating elements, sensors and detection devices, that come in contact with the water, are machined in brass or made of copper to help resist corrosion. Standard 1 _ inch, flanged screw-type heating elements are utilized which are interchangeable with heating elements available at local hardware stores.

SAFETY AND MAINTENANCE: The tankless water heater was designed with a complete array of dependable safety features to prevent harm to the user and the heater. There are several redundant safety features as well. They include, dual high temperature switches on independent circuitry in addition to the control's internal high temperature shut down. Dual low level detectors are used to prevent dry firing of the heating elements and a leak detector is mounted on the casing that in the event of a leak, sounds an alarm to the user. Although the control board is protected against electrical surges, additional heater protection is achieved when the relays are opened during periods of standby, providing no path for the surge to reach the heating elements. Also, the chamber is designed with a patented venting system that continuously vents harmful gasses and air during operation. The microprocessor control is programmed to provide self diagnostics that significantly reduces trouble shooting and service time. In the event of a problem with the heater, the control emits a visual or optional built-in audible code. There is no maintenance required of the unit. However, there are clean-out plates below the heater chamber to allow removal of sand and grit that may build-up from a well water system.

POWER RATING: The four-chamber models contain four electric heating elements whose combined wattage is the total power rating of the heater. For instance, the standard RA-28 model contains four 7000 watt elements for a total of 28,000 watts, or 28 kilowatts (kW) of power. The two-chamber model, RA-14, contains only two 7000 watt elements for a total power rating of 14,000 watts, or 14 kilowatts (kW). However, because of tankless water heater's "Power Sharing" technology, the heater may not always use the maximum available power. The power output can vary with flow rate and temperature rise. Refer to the Product Specifications Table for the maximum power ratings of each model.

HEATING OUTPUT: The heating output of the tankless water heater is simply the total kilowatt power rating of the combined heating elements converted to BTUs using 3,413 BTU/kW. For instance, the RA-28 has a total power rating of 28 kW or a 95,564 BTU heat output rating. The four-chamber models have the higher output ratings; 61,434 BTUs for the RA-18 model, and 75,086 BTUs for the RA-22 model. The lower output two-chamber models, are; 47,782 BTUs for the RA-14, 37,543 BTUs for the RA-11, and 30,717 BTUs for the RA-9. These ratings vary with the operating voltage or service voltage to the heater. Refer to the Product Specifications Table for the BTU ratings of each model.

VOLTAGE RATING: Tankless water heaters are manufactured with common 240 volt (AC) heating elements designed for optimum operation on a standard residential 240 volt (AC) electric service. Also, the tankless heater will operate at 208 VAC, a typical commercial voltage, with standard 240 VAC heating elements. However, when operating the heater at 208 VAC, the power rating and the heat output rating is significantly reduced. Models can be special ordered with 208 VAC heating elements to help maximize the power and heating output. Refer to the Product Specifications Table for details on the various voltage ratings.

MAXIMUM CURRENT RATING: Each Model has a maximum electrical current rating (or amp rating) equivalent to the sum of the heating element ratings. For example, a four-chamber model, RA-28, operating at 240 VAC has four heating elements, each with a maximum rating of 29 amps. The maximum current rating or total current rating of the RA-28 is therefore 116 amps or the sum of the four heating elements. However, because of tankless water heater's "Power Modulating Technology", the actual current measured during relatively low flow rates and/or low temperature rises can be less than the maximum rating of the heater during operation. Refer to the A (max) or maximum amp rating under "Electrical" in the Product Specifications Table for each model.

TEMPERATURE RISE: The temperature rise must be determined in order to help choose the appropriate tankless water heater. The rise can be determined by knowing the input water temperature and the desired output temperature of the heater. The unit's output temperature is typically set for about 120 degrees F at the factory. Therefore, if the input or cold water inlet temperature is 50 degrees F, then the temperature rise is the difference or 70 degrees F. If the desired output temperature is 125 degrees F, then the temperature rise would be 75 degrees F. With the temperature rise determined, the Product Specification Table provides the associated flow rate capacity of the various models.

FLOW RATE: The flow rate for each model is given in the "Temperature Rise" table of the Product Specification Table. Along with the temperature rise, the flow rate must also be determined in order to choose the appropriate tankless water heater. The flow rate is determined by the type of faucet and also, life style. Refer to the chart below for typical faucet flow rates in the home. However, if the desired life style in the home requires running multiple faucets at the same time, then the flow rates must be added together to determine the peak flow demand. The model or the possibility of multiple tankless water heaters should be selected to match the peak flow rate.

Below are typical flow rates for new residential construction. There may be exceptions with new designer type fixtures and faucets. For instance, large custom body spa showers, whirl pool and Jacuzzi tubs may have faucets with flow rates ranging from 7 gpm to 14 gpm. However, a combination of multiple tankless water heaters (preferably plumbed in a parallel configuration) can be installed to match these higher flow rates. The same peak design approach would be necessary for the anticipated life style of multiple flow rates occurring at the same time. Otherwise, use the table below and match the tankless water heater according to the peak flow and associated temperature rise of a single tub or shower.

Typical Flow Rates in Gallons per Minute (gpm)

Fixture Type
Lavatory Bathtub Shower Kitchen Sink Pantry Sink Laundry Sink Dishwasher

Flow Rates 0.8-1.5 2.0-4.0 1.5-3.0 1.0-1.5 1.5-2.5 2.5-3.0 2.0-3.0