What is the normal range for fire over draft?

The normal range for fire over draft is typically presented as values indicating the draft conditions within a chimney or venting system used for combustion appliances. In this context, a negative value signifies that there is a draft being established where air is being drawn into the combustion area from outside.

The range of -0.1 to -0.03 indicates a condition where there is a slight draft that is effective enough to allow proper air flow into the system for efficient combustion. This is crucial for maintaining safe and efficient operation of heating systems. If the draft is too high or too low, it can lead to inefficiencies, incomplete combustion, or dangerous conditions such as backdrafting.

In comparison, other ranges provided in the question either suggest a more negative or a less negative draft than what is considered ideal, which could indicate insufficient combustion air leading to unsafe or inefficient operation. The specific selection of -0.1 to -0.03 reflects the balance necessary for optimal performance in a properly functioning heating system.