What could be causing the copper green smells in my house when the furnace turns on?
If by Copper-Green you mean any of the copper-naphthalene wood preservatives out there used to prevent wood rot, and it was applied to the studding, etc. that supports this fireplace shell:

These products are not to be used within living spaces or in construction where the fumes will be pulled into the living space. 

Apply caulking to seal up the air gaps that allow air to get in from the external structure.

If any of it is inside the living space, it will need to be ripped out.

If no Copper Naphthalene products were used for wood preservation and rather it's the acrid creosote smell of air being drawn down the chimney despite the damper being closed, then you've got another problem altogether. Your secondary air intake for your furnace is plugged or you are missing one and the negative pressure in the living space is drawing air from wherever it can find ventilation.

Note: Hardi-Plank as produced by James Hardie is a cement board product that needs no preservatives to prevent rot.