Furnace Temperature Rise and Derived Airflow
The supply-minus-return temperature rise checked against the rating-plate range (default 40 to 70 F), and the airflow derived from the heat output via Qs = 1.08 x CFM x delta-T: from return / supply temperatures, furnace input, and efficiency, the rise, the output, and the CFM, with a rise-low / in-range / rise-high reading. The rating plate governs.
Formula and source
delta_T = supply_air - return_air; output = input x efficiency / 100; CFM = output / (1.08 x delta_T). Verdict checks delta_T against the rating-plate rise range.
First-principles sensible-heat relation Qs = 1.08 x CFM x delta-T (public); the 1.08 air factor and efficiency are editable.
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