REU-2532FFU Series 22 Rinnai
13. Water Flows
A simple calculation of the water flow rate, in gallons per minute, can be made using the chart on the
next page, or simply using formula provided below. The chart on the following page indicates the water
flow from the Continuum at various temperature rises up to a 140 degree rise.
a. How to read the charts:
The vertical plane indicates water flow in gallons per minute, and the horizontal plane indicates the
temperature rise. The chart shows flow rates up to a 140 degree rise. Therefore, the water flow chart can
be used to help you size your applications, if you know the temperature rise needed. The temperature
rise is the difference between the temperature of the incoming water and the selected temperature at the
remote control(s). Another name used in place of temperature rise, is delta T.
Select the appropriate temperature rise. Draw a vertical line up the graph from the selected temperature
rise until it intersects the curve. The point at where these lines intersect indicates flow at that
temperature rise.
b. How to calculate water flows:
The following information is an outline of the formula required to measure accurately the flow rate in
gallons per minute, as well as being the base for the chart on the next page. The formula below can be
utilized when you know the following information, the Btu’s and efficiency of the appliance, and the
delta T you are dealing with. If this information is known follow the example below to determine your
flow rate. The example below assumes the appliance’s Btu rating is 180,000, the efficiency is .82 and
the delta T is 55 degrees.
EXAMPLE:
BTU’s
÷÷
÷÷
÷ AT x 500 = GPM’s
GPM’s = (180,000 BTU’s x .82 efficiency rating)
÷÷
÷÷
÷ ÄT x 500
GPM’s = 147,600 ÷(Requested water temperature – incoming water temperature) x 500
GPM’s = 147,600 ÷ (120 °F requested – 65 °F incoming) x 500
GPM’s = 147,600 ÷ (55 °F delta T x 500)
GPM’s = 147,600 ÷ 27,500
GPM’s = 5.367
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