Setting Supply Air Temperature Rise - Thermo Pride MHA1-50N Installation And Service Manual

All installations and services must be performed by qualified service personnel.
If long, rather poorly defined, mostly yellow in color, and nearly opaque burner
flames are observed, this is an indication the quality of combustion is poor.
(Under adverse conditions, black smoke and some sooting may be noticeable as
well.) Some of the causes of poor combustion are, too high an input rate ("over-
firing"), too little or a contaminated supply of combustion air, or a partially
blocked heat exchanger or vent terminal. Should any of these conditions
occur, they must be corrected immediately. Call your qualified heating
contractor for assistance.
D. Setting Supply Air Temperature Rise
All MHA1/MDA1models are designed and wired at the factory for a blower speed
during heating that should result in an approximate temperature rise of 70°F. The
temperature rise through the heating section, for any given blower speed may
vary depending on a number of factors. A few of these factors are, changes in
the actual resistance of the duct system to airflow at any time, de-rating of the
appliance due to elevation, fouling of the heat exchanger surfaces, and changes
in the fuel gas heating value. In general, a lower temperature rise through the
heating section will result in higher heating efficiency.
Temperature rise = supply air temperature - return air temperature.
After 15 to 20 minutes of continuous operation, the temperature rise through the
furnace must fall within a range of 55° to 85° F. If the outlet or supply duct
temperature is too high, check to make sure the return air filter is clean, the
return air registers are free from obstruction, the outlet registers are properly
adjusted and clear, and the supply and return air ducts are open.
The circulating air blower is not moving enough air if the supply air temperature
is still too high. Before proceeding further, turn off the power supply to the
appliance and remove the blower access door. The speed of the blower must be
increased by changing the speed tap from the motor to the next higher tap, refer
to Figure 8.
Figure 10: Typical Observation of Main Burner Flames
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