A thermostatic control may delay turning on the blower until the plenum has reached what temperature?

The choice of 140°F is significant because it aligns with the standard operating principles of many HVAC systems, particularly in regard to ensuring efficient heat distribution and preventing blower operation until there is adequate heat in the plenum.

When the plenum reaches around 140°F, it typically indicates that the system has generated enough heat to efficiently warm the air before it is circulated throughout the living spaces. This temperature helps prevent the system from blowing cool or inadequately warmed air, which can lead to discomfort and inefficiency as well as increased wear on the blower motor.

In many HVAC setups, a delay in blower activation helps to optimize system performance, ensuring that the air being distributed is at a comfortable and effective temperature. This principle is crucial for maintaining both comfort and energy efficiency in heating applications.