M R S E R I E S D U C T H E A T E R
S Each KW produces 3413 BTUH. Divide the BTUH of heat needed by 3413 to find the KW needed. Use the chart below to find the minimum airflow needed. You will need to know the maximum inlet air temperature of the Heater. The outlet air from a Heat Pump (sometimes 110 deg. F.) would be the inlet air to an auxiliary Heater. You must also know the KW per Sq. Ft. of the MINIMUM Duct Area (KW/SQ. FT. MDA.) for the Heater. An Example is worked out below: EXAMPLE: Using a 12 KW Heater designed for minimum duct size 8" x 16" and being the only Heat in a residence. You expect inlet air to the Heater will be 77 deg. F. maximum. 8" x 16" divided by 144 = .888 Sq. Ft. of Heater MINIMUM Duct area design. 12 (KW) divided by the .888 = 13.5 which is the KW/SQ. Ft. MDA. Locatethe13.5 along the top side of the chart and from there draw a vertical line downward until the 77 deg. F. inlet air line is intersected. From point of intersection draw a horizontal line to the left side of the chart to the answer of 800 FIRM (Velocity) of air minimum required over the Heater. To convert to CFM multiply the answer by the Sq. Ft. of the Heater MINIMUM duct area design. In the example 800 multiplied by .888 would be 710 CFM. These minimum airflow requirements should be met at any point over the face of the Heater. If Heaters are used in ducts larger than the Heater minimum duct design, reliable means should be used to assure the proper airflow through the Heater.
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