SELECTION CRITERIA

Below is a list of the basic information that is needed for selecting the proper tankless water heater model:

• Peak flow rate in gallons per minute (GPM).
• Inlet water temperature or cold water temperature.
• Electrical capacity (amps) and the service voltage (VAC).
• Desired output temperature or hot water temperature.

Additional information may be necessary for space heating applications, such as the following:

• Heat loss rate (BTU/hr) of the home or building.
• Flow rate of the circulating pump in gallons per minute (GPM).

Peak Flow Rate:

Below are typical flow rates for new residential construction. There may be exceptions, such as 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 (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 heater according to the peak flow and associated temperature rise of a single tub or shower. Also, refer to the Product Specification Tables in the "Description & Specifications" section of the Product Manual for the flow ratings of each tankless water heater model.

Typical Flow Rates in Gallons per Minute (gpm)

Measuring flow rates at a faucet can be done by simply using a common one-gallon bucket or a similar container of known liquid capacity. The approximate flow rate can be determined by simply turning on the faucet in question to full flow, and timing how long it takes to fill the one gallon bucket. If it takes 20 seconds to fill the one gallon bucket, then the flow rate is 3 gallons per minute or 3 gpm. If it takes 15 seconds to fill the bucket, then the flow rate is 4 gpm. Simply divide 60 seconds (which is one minute) by the recorded time to fill the bucket to arrive at the flow rate.

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Inlet Temperatures:

Measuring the inlet temperature can be determined with a common cooking or baking thermometer. Simply turn on the cold water (not the hot) and place the thermometer into the flow. For best results, let the water run for approximately one to two minutes before taking the reading. This allows purging of any ambient temperature water sitting in the lines. It is important to know the inlet water temperature so that the temperature rise can be determined. The temperature rise and associated flow rating of the faucets are necessary for the proper model selection.

Inlet water temperatures can vary depending on geographical location, season of the year and the type of water system. For instance, Southern Georgia and Florida have inlet water temperatures typically between 60 and 70 degrees F. Mountainous areas, such as the Rockies may have water temperatures as low as 40 degrees F. In the middle and northern sections of the U.S., temperatures generally range from 45 to 55 degrees F. Most well water systems (except in mountainous areas) generally remain constant at 50 to 55 degrees year round.

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Electrical Capacity:

Most electric homes today have 200 amp electric services. This has become the standard over the past 10 years or so in new home construction. However, homes that utilize gas for space heating, water heating and cooking may have 100 or 150 amp electric service. It is important to know whether the electrical capacity of the home or building is sufficient for the tankless water heater. In most cases, an all electric home of 3000 square feet or less with a 200 amp whole-house electric service will have the electrical capacity for one RA-28. The RA-28 is sufficient to provide all the hot water for a home of this size containing 2 _ or 3 baths with standard flow rate faucets.

It will be necessary however, to have a qualified electrician calculate the electrical loads in the home or building with the load of the selected model(s). The load calculations should be done according to the National Electric Code (NEC), 220-30 and 220-31, Optional Calculation. Refer to the "Electrical Service Requirements & Sample Calculations" section of the Product Manual for how the NEC rules apply to the tankless water heater.

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