What happens to the air flow in a furnace when the pressure increases?

When the pressure in a furnace increases, the air flow typically decreases due to increased resistance within the system. This phenomenon occurs because higher pressure creates a situation where more force is required to move the air through the ductwork and components of the furnace. As resistance increases, the ability of the system to maintain or increase air flow diminishes.

In many heating systems, proper air flow is essential for efficient combustion and heating. If the flow decreases due to increased pressure and resistance, this can lead to inadequate combustion and may affect the overall performance of the furnace.

The other options suggest scenarios that do not align with how pressure affects airflow in a typical furnace system. For instance, airflow remaining constant regardless of pressure ignores the principle that as resistance increases, flow becomes more limited. An increase in air flow due to higher pressure is also inconsistent with the physical attributes of how air moves through tight spaces where pressure rises. Meanwhile, redirecting air to a safety vent is a specific safety feature that relies on other parameters in the system rather than simply the effects of pressure on airflow.