Clearances to combustibles is a critical issue.  I think it is important
to have a clearance specified for the "typical" hand built masonry stove
in any code language we get.  

Proper use of a "typical" masonry stove, as we may all agree, would be
safe at 4" as proposed.  However this could be an unsafe situation in
the future as the homes the heaters are built in may be sold to people
ignorant of masonry stoves. 

 An unaware person could keep a constant fire going all weekend then, 4"
clearance to combustibles does not adequately insure public safety.
Masonry heat is not a tradition in America so people who buy homes
containing a masonry heater are unlikely know how to use it.  They may
try to heat 2-3 times the area the heater is designed to heat. This also
could be a safety concern. 

 It should be required in the code that all masonry heaters be "labeled"
with instructions of proper use and maintenance, this is just as
important for safety as wall thickness or material used.

The code should also say "or distances specified according to the
manufacturer's instructions", this will allow for the development of our
industry (we all win).  Most codes contain "or per manufacturers
instructions" language, building inspectors expect and accept it.

Like all industries we have manufacturers who build and design their
products differently.  Our manufacturers are not second class or fly by
night operations.  Are we afraid of inexperienced capitalists entering
the market in the future and reducing typical clearances and wall
thickness without any testing? Come on!   In America, our sue happy
society?  Could we believe that any mason who pre cuts brick or stone
would call himself a manufacturer and produce his own instructions (that
would be accepted as legitimate by the building inspectors).  Masons
will be likely to follow the typical rules & methods that we have been,
but will have code reference to give credibility.    
 
Considering the potential for "inappropriate use" on unlabeled units as
a factor it is a bigger safety concern that 4" clearance to the
"typical" masonry heater spec may be to close, than the fear that  the
"per manufacturer clause" would result in unsafe installations.   

Though I wish it was voiced before that is my opinion.  Anyone agree?
Stan Sackett