As for code, NYC is tightly regulated. Go to this document and read Article 19, (section 848)
http://www.nyc.gov/html/dob/downloads/bldgs_code/bc27s14.pdf
some items of note:
Qualifications of installer.-
(1)
Installation shall be made only by persons authorized
by the manufacturer to install the specific equipment in
question.
(2) The installer shall certify to the registered architect
or licensed professional engineer who has filed the
application that the installation is in full compliance
with the terms of the listing, acceptance and the
manufacturer's instructions.
(3) For retrofit installations in occupied residential
dwellings, the installer shall have a home improvement
contractor's license from the department of consumer
affairs.
(c) Controlled inspection. -Installation shall be subject
to controlled inspection to ensure that the installation is
in accordance with:
(1) the structural elements shown on the approved plans,
(2) the fire protection requirements, and
(3) the listing, acceptance and the manufacturer's installation
recommendations.
(d)
Environmental requirements.- All solid fuel burning
appliances shall comply with the requirements of the air
pollution control law, chapter one of title twenty-four of
this code.