Koko wrote:can I assume I would get three time the heat output
It depends!! I would say it is safe to assume you will get some multiplier more BTU's, but what that multiplier is exactly would be near impossible to calculate outside of a controlled lab experiment.
To start, the BTU rating may be figured differently for different mfg's. Some ratings may be input BTU's & some output BTU's. And then you get into the efficiency of the stove transferring the BTU's it has inside the firebox out to the room/building itself. What is the sq ft area of the stove available to radiate the heat, how well is airflow around this area accomplished, how well is heat extracted from exhaust, etc, etc.
I can see this one growing into quite a few pages!!