Minimum required hearth extension for fireplace insert

[DIYRenovator]

I have a fireplace insert (wood burning stove) inside a masonry fireplace. I am installing hardwood floor and would like to keep the minimum size for the hearth extension. The following table shows the required size of the hearth extension:



My questions are:

1. Is the fireplace opening calculated based on the door size of the fireplace insert (wood stove) or the opening size of the masonry fireplace?

2. I have a detachable fan blower unit in front of the fireplace insert as shown in the picture. Is the hearth extension (front of the opening) calculated from the door of the fireplace insert or from the edge of the fan blower unit?



Thanks!

 

[begreen]

The distance is measured from the stove glass. It is always good to make the hearth extension a little deeper than required if possible.