What is the approximate pressure inside an induced draft heat exchanger for a mid-efficiency furnace?

In a mid-efficiency furnace, the pressure inside an induced draft heat exchanger is typically slightly positive, which allows for proper exhaust of combustion gases. A reading of approximately +2 inches of water column (W.C.) indicates that the pressure is above atmospheric pressure, which is essential for ensuring that exhaust gases are effectively drawn out of the furnace and vented outside of the home. This positive pressure helps to prevent the backflow of combustion byproducts and contributes to the overall efficiency and safety of the heating system.

Options with negative pressure values, such as -2" W.C., -4" W.C., or even a higher positive pressure of +4" W.C., do not align with the operational characteristics of mid-efficiency furnaces. Negative pressure could suggest issues with venting or a malfunction in the draft system, while excessively high positive pressure could indicate overpressurization risks that aren't typical for these types of systems. Therefore, the +2" W.C. reading represents a balanced and efficient operating state for the induced draft heat exchanger in a mid-efficiency furnace.